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National audience; Le projet "REAGIR" vise tout d’abord à identifier de nouvelles substances actives contre les populations d’Ae. aegypti résistantes aux pyréthrinoïdes en ciblant particulièrement le stade adulte. Trouver ces alternatives adulticides passe soit par le criblage de molécules d’origine naturelle ou synthétique, nouvelles ou existantes dans d’autres domaines, soit par l’amélioration de l’efficacité d’insecticides connus.

Le projet "REAGIR" vise tout d’abord à identifier de nouvelles substances actives contre les populations d’Ae. aegypti résistantes aux pyréthrinoïdes en ciblant particulièrement le stade adulte. Trouver ces alternatives adulticides passe soit par le criblage de molécules d’origine naturelle ou synthétique, nouvelles ou existantes dans d’autres domaines, soit par l’amélioration de l’efficacité d’insecticides connus.

Bemisia tabaci est un insecte ravageur d'importance mondiale de par sa capacité à transmettre des phytovirus. Trois espèces d'aleurodes coexistent à La Réunion : l'espèce indigène IO, et deux espèces exotiques MEAM1 et MED-Q, qui ont successivement envahi l'île en 1997 et 2010. La principale stratégie de lutte contre ces espèces est l'utilisation d'insecticides, ce qui peut mener à l'émergence de résistances. Le principal objectif était de comprendre l'évolution de la distribution de ces espèces dans les agrosystèmes insulaires, au regard de leur spectre de résistance aux insecticides dans un contexte d'hybridation interspécifique. A cette fin, des aleurodes ont été échantillonnés dans 56 sites, génotypés pour 11 marqueurs microsatellites et pour deux loci kdr impliqués dans la résistance aux pyréthrinoïdes. Quinze populations ont été phénotypées pour la résistance à la pymétrozine et à l'acétamipride, et le coût de la résistance à l'acétamipride a été évalué. Les deux espèces envahissantes se retrouvent principalement dans les agrosystèmes, et possèdent des mutations de résistance kdr. La plupart des populations de MEAM1 sont résistantes à l'acétamipride, à la pymétrozine ou aux deux insecticides. La résistance à l'acétamipride ne semble pas soumise à un coût. L'espèce indigène IO a été principalement échantillonnée dans les zones non agricoles, ou en bordure d'agrosystèmes. Elle n'a aucune mutation de résistance aux pyréthrinoïdes et est sensible aux insecticides testés. Enfin, l'hybridation interspécifique (MEAM1-IO) observée ne conduirait pas à l'introgression de mutations résistantes chez l'espèce indigène, mais possiblement à l'introgression de sensibilité chez MEAM1.

BACKGROUND: Global and intensive use of insecticides has led to the emergence and rapid evolution of resistance in the major pest Bemisia tabaci (Gennadius). In La Reunion, an island of the South West Indian Ocean, three whitefly species coexist, two of which are predominant, the indigenous Indian Ocean (IO) and the invasive Middle East Asia Minor 1 (MEAM1) species. To assess the resistance level of both of these species to acetamiprid and pymetrozine, whitefly populations were sampled at 15 collection sites located all over the island in agroecosystems and natural areas, and tested using leaf‐dip bioassays. We also investigated the potential cost of resistance to acetamiprid by measuring six fitness‐related traits for MEAM1 populations that displayed different resistance levels. RESULTS: IO was mainly found in natural areas and was susceptible to both acetamiprid and pymetrozine. MEAM1 populations displayed evidence of high resistance to pymetrozine, whereas resistance to acetamiprid was more variable. No fitness‐related costs were associated with this resistance in MEAM1 populations. CONCLUSION: This is the first assessment of the susceptibility to insecticides for B. tabaci IO species. For the time being, no resistance to the tested insecticides has evolved in this species despite (i) its presence in agroecosystems and their surroundings, and (ii) its close proximity to, and possible hybridization with, the MEAM1 species. In contrast, with continuous selection pressure of insecticide treatments and in the absence of fitness cost to resistance, the invasive exotic species MEAM1 will continue to threaten agriculture in La Reunion. © 2019 Society of Chemical Industry.

A range of mosquito species that belong to the Culicidae family are responsible for the worldwide transmission of infectious arboviral diseases such as dengue fever, Zika, West Nile fever and Chikungunya fever. Spain is at risk of arbovirus outbreaks, as various arboviral diseases are frequently introduced and it has established competent vector populations. Autochthonous human cases of West Nile virus have been reported infrequently since 2004, and since October 2018 three autochthonous human case of dengue fever have been confirmed. In response to an outbreak of any arboviral disease, space spraying or fogging will be implemented to control adult mosquito populations. To ensure adulticiding is cost-effective, the insecticide susceptibility status of vectors throughout Catalonia, an autonomous region in north-eastern Spain, was assessed through standardized WHO tube and CDC bottle bioassays. All Culex pipiens populations tested were resistant to at least one of the pyrethroids tested, whereas Aedes albopictus populations were susceptible to all pyrethroids tested. More detailed studies on the Cx. pipiens populations from the Barcelona area (the capital and largest city of Catalonia) revealed resistance to all four classes of public health insecticides available (pyrethroids, carbamates, organophosphates and organochlorides). All Ae. albopictus populations were susceptible to those classes, except for one of the tests performed with pirimiphos-methyl (an organophosphate). Pyrethroids are currently the first line chemical class to be used in space spray operations in response to an outbreak of an arboviral disease. While pyrethroids can be effective in reducing Ae. albopictus populations, this class may not be effective to control Cx. pipiens populations.

International audience; Vector control constitutes a fundamental approach in reducing vector density and the efficient option to break malaria transmission in Africa. Malaria vectors developed resistance to almost all classes of insecticides recommended by WHO for vector control in most places of African countries and may compromise the vector control strategies. This study updated the resistance status of Anopheles gambiae complex populations to insecticides recommended for vector control in the western part of Burkina Faso. Insecticide susceptibility bioassays were performed on seven natural populations of An. gambiae complex from western Burkina Faso in the 2016 rainy season using the WHO protocol. Biochemical assays were carried out according to the WHO protocol on the same populations to estimate detoxifying enzymes activities including non-specific esterases (NSEs), oxidases (cytochrome P450) and Glutathione-S-Transferases (GSTs). Polymerase Chain Reactions (PCRs) were performed for the identification of the An. gambiae complex species as well as the detection of kdr-west and ace-1 mutations. Susceptibility bioassays showed that An. gambiae complex was multi-resistant to pyrethroids, DDT and carbamates in almost all areas. The mortality rates ranged from 10 to 38%, 2.67 to 59.57% and 64.38 to 98.02% for Deltamethrin, DDT and Bendiocarb respectively. A full susceptibility (100%) to an organophosphate, the Chlorpyrifos-methyl, was observed at the different sites. Three (3) species of the An. gambiae complex were identified: An. gambiae s.s, An. coluzzii and An. arabiensis. The frequencies of the kdr-w mutation were highly widespread (0.66 to 0.98) among the three species of the complex. The ace-1 mutation was detected at low frequencies (0 to 0.12) in An. gambiae s.s and An. coluzzii. A high level of GSTs and NSEs were observed within the different populations of the An. gambiae complex. Several mechanisms of insecticide resistance were found simultaneously in the same populations of An. gambiae complex conferring high multi-resistance to DDT, Carbamate and Pyrethroids. The full susceptibility of An. gambiae complex to organophosphates is a useful data for the national malaria control program in selecting the most appropriate products to both maintain the effectiveness of vector control strategies and best manage insecticide resistance as well as developing new alternative strategies for the control of major malaria vectors in Burkina Faso.

Simple Summary The moth fall armyworm (Spodoptera frugiperda) is a major agricultural pest insect damaging a wide range of crops, especially corn. Field evolved resistance against Bacillus thuringiensis (Bt) toxins and synthetic insecticides has been repeatedly reported. While the fall armyworm is native to the Americas, its biological invasion was first reported from West Africa in 2016. Since then, this pest has been detected across sub-Saharan and North Africa, Asia, and Oceania. Here, we examine the geographical distribution of mutations causing resistance against Bt or synthetic insecticides to test if the invasion was accompanied by the spread of resistance mutations using 177 individuals collected from 12 geographic populations including North and South America, West and East Africa, India, and China. We observed that Bt resistance mutations generated in Puerto Rico or Brazil were found only from their native populations, while invasive populations had higher copy numbers of cytochrome P450 genes and higher proportions of resistance mutations at AChE, which are known to cause resistance against synthetic insecticides. This result explains the susceptibility to Bt insecticides and the resistance against synthetic insecticides in invasive Chinese populations. This information will be helpful in investigating the cause and consequence associated with insecticide resistance. Abstract Field evolved resistance to insecticides is one of the main challenges in pest control. The fall armyworm (FAW) is a lepidopteran pest species causing severe crop losses, especially corn. While native to the Americas, the presence of FAW was confirmed in West Africa in 2016. Since then, the FAW has been detected in over 70 countries covering sub-Saharan Africa, the Middle East, North Africa, South Asia, Southeast Asia, and Oceania. In this study, we tested whether this invasion was accompanied by the spread of resistance mutations from native to invasive areas. We observed that mutations causing Bt resistance at ABCC2 genes were observed only in native populations where the mutations were initially reported. Invasive populations were found to have higher gene numbers of cytochrome P450 genes than native populations and a higher proportion of multiple resistance mutations at acetylcholinesterase genes, supporting strong selective pressure for resistance against synthetic insecticides. This result explains the susceptibility to Bt insecticides and resistance to various synthetic insecticides in Chinese populations. These results highlight the necessity of regular and standardized monitoring of insecticide resistance in invasive populations using both genomic approaches and bioassay experiments.

The control of parasitic nematodes impacting animal health relies on the use of broad spectrum anthelmintics. However, intensive use of these drugs has led to the selection of resistant parasites in livestock industry. In that respect, there is currently an urgent need for novel compounds able to control resistant parasites. Nicotine has also historically been used as a de-wormer until modern anthelmintics were marketed. The pharmacological target of nicotine has been identified in nematodes as acetylcholine- gated ion channels. Nicotinic-sensitive acetylcholine receptors (N-AChRs) therefore represent validated pharmacological targets than remain largely under-exploited. In the present study, we developed an automated larval migration assay (ALMA) and showed that nicotinic derivatives (anabasine/nornicotine) efficiently paralyzed a multiple (benzimidazoles/levamisole/ pyrantel/ivermectin) resistant field isolate of Haemonchus contortus. Additionally, using Caenorhabditis elegans as a model, we confirmed that the N-AChRs subtype contributes to the anthelmintic effect of nicotinic analogs. Interestingly, the functional expression of the homomeric N-AChR from C. elegans and the distantly related horse parasite Parascaris equorum in Xenopus oocytes highlighted some striking differences in their respective pharmacological properties towards nicotine derivative sensitivity. Noteworthy, nicotine and anabasine were more potent than ACh in activating the P. equorum N-AChR as revealed by their respective EC50 values (2.9 ± 0.5 μM and 1.7 ± 0.1 μM versus 6.4 ± 1.1 μM, respectively), unlike nornicotine (34.9 ± 7.2 μM) whereas the potency series for the C. elegans N-AChR was Nic > ACh = Ana > Nor. Taken together these results validate the exploitation of the N-AChRs of parasitic nematodes as targets for the development of resistance-breaking compounds.

Ticks are strict blood-feeding arthropods (Acari), which represent a major health issue for wild or domesticated animals and humans, due to their potential to transmit disease agents. Control of ticks is increasingly difficult due to the development of drug-resistant parasites. Ligand-gated ion channels of the tick central nervous system are the primary targets of acaricides. Among those receptors, the γ-aminobutyric acid-gated chloride ion channels (GABACls) are the main synaptic inhibitory receptors. Lotilaner is a recently developed parasiticide from the isoxazoline chemical class that was shown to be a non-competitive antagonist of GABACls from the livestock tick Rhipicephalus microplus. In the present study, we characterized the GABACls from the European tick species Ixodes ricinus. We extracted RNAs from Ixodes ricinus nymphs. Taking advantage of the phylogenetic closeness of I. ricinus and R. microplus in the Arthropoda phylum, we identified the I. ricinus GABACl subunit homologue. The cDNA encoding the Iri- GABACl was cloned and the corresponding in vitro synthesized cRNAs were micro-injected into Xenopus laevis oocytes to investigate its pharmacological properties. Functional expression and two-electrode voltage clamp studies demonstrated that the GABACl subunit formed a homomeric receptor gated by GABA. Importantly, the insecticides like lotilaner, fipronil and picrotoxin efficiently blocked the GABA currents as previously observed for the R. microplus GABACl. Surprisingly, I. ricinus GABACl was not sensitive to the pesticide dieldrin, suggesting a potential naturally existing resistance mechanism involving alternative exons. Here we report the functional characterization of the first GABACl of I. ricinus demonstrating that it is an important molecular target for lotilaner. Transcriptomic analysis of I. ricinus are in progress to identify new acaricidal targets.

Drug resistance in the parasites field, including the cosmopolitan lice (Pediculus humanus), and the prevalence increasing despite the marketing of new therapies are an important challenge for our societies. The major pharmacological targets of insecticides like pyrethrins, malathion, spinosad and ivermectin (also used as nematicide and acaricide) are the ligand gated ion channels present in the nervous system of insects. Currently, targets of these molecules remain largely unknown in body lice. Among those channels receptors, γ-aminobutyric acid gated chloride ion channels (GABACl) are the main synaptic inhibitory receptors in insects, making them pertinent pharmacological targets. In the present study, we identified and characterized the targets of insecticides in lice to decipher the mode of action of insecticides in Pediculidae. Research in the genomic databases of Pediculus humanus allowed us to identify a GABACl subunit encoded by the Resistance to dieldrin (Rdl) gene. We cloned the corresponding full-length cDNA into a transcription vector and performed in vitro synthesis of the cRNAs, which were injected in the Xenopus oocysts system to reconstitute functional channels. Two-electrode voltage clamp recordings showed that Phh-RDL assemble into a homomeric receptor sensitive to different insecticides like fipronil, picrotoxin and lotilaner, a novel class of ectoparasiticide agent using to treat ticks and fleas of dogs (CredelioTM, Elanco). These results correlated with the efficacy of these drugs on lice in vivo. In conclusion, we report the functional characterization of the first GABACl of Pediculus humanus humanus. These results contribute to our understanding of the mode of action of insecticide compounds and will allow the development of new therapeutic strategies to control lice infestations.

The cotton bollworm, Helicoverpa armigera (Hu¨bner) is one of the most serious insect pest species to evolve resistance against many insecticides from different chemical classes. This species has evolved resistance to the pyrethroid insecticides across its native range and is becoming a truly global pest after establishing in South America and having been recently recorded in North America. A chimeric cytochrome P450 gene, CYP337B3, has been identified as a resistance mechanism for resistance to fenvalerate and cypermethrin. Here we show that this resistance mechanism is common around the world with at least eight different alleles. It is present in South America and has probably introgressed into its closely related native sibling species, Helicoverpa zea. The different alleles of CYP337B3 are likely to have arisen independently in different geographic locations from selection on existing diversity. The alleles found in Brazil are those most commonly found in Asia, suggesting a potential origin for the incursion of H. armigera into the Americas.

The use of pesticides made it possible to increase yields, simplify cropping systems, and forego more complicated crop protection strategies. Over-reliance on chemical control, however, is associated with contamination of ecosystems and undesirable health effects. The future of crop production is now also threatened by emergence of pest resistance and declining availability of active substances. There is therefore a need to design cropping systems less dependent on synthetic pesticides. Consequently, the European Union requires the application of eight principles (P) of Integrated Pest Management that fit within sustainable farm management. Here, we propose to farmers, advisors, and researchers a dynamic and flexible approach that accounts for the diversity of farming situations and the complexities of agroecosystems and that can improve the resilience of cropping systems and our capacity to adapt crop protection to local realities. For each principle (P), we suggest that (P1) the design of inherently robust cropping systems using a combination of agronomic levers is key to prevention. (P2) Local availability of monitoring, warning, and forecasting systems is a reality to contend with. (P3) The decision-making process can integrate cropping system factors to develop longer-term strategies. (P4) The combination of non-chemical methods that may be individually less efficient than pesticides can generate valuable synergies. (P5) Development of new biological agents and products and the use of existing databases offer options for the selection of products minimizing impact on health, the environment, and biological regulation of pests. (P6) Reduced pesticide use can be effectively combined with other tactics. (P7) Addressing the root causes of pesticide resistance is the best way to find sustainable crop protection solutions. And (P8) integration of multi-season effects and trade-offs in evaluation criteria will help develop sustainable solutions.

Many studies have shown the role of agriculture in the selection and spread of resistance of Anopheles gambiae s.l. to insecticides. However, no study has directly demonstrated the presence of insecticides in breeding sources as a source of selection for this resistance. It is in this context that we investigated the presence of pesticide residues in breeding habitats and their formal involvement in vector resistance to insecticides in areas of West Africa with intensive farming. This study was carried out from June to November 2013 in Dano, southwest Burkina Faso in areas of conventional (CC) and biological cotton (BC) growing. Water and sediment samples collected from breeding sites located near BC and CC fields were submitted for chromatographic analysis to research and titrate the residual insecticide content found there. Larvae were also collected in these breeding sites and used in toxicity tests to compare their mortality to those of the susceptible strain, Anopheles gambiae Kisumu. All tested mosquitoes (living and dead) were analyzed by PCR for species identification and characterization of resistance genes. The toxicity analysis of water from breeding sites showed significantly lower mortality rates in breeding site water from biological cotton (WBC) growing sites compared to that from conventional cotton (WCC) sites respective to both An. gambiae Kisumu (WBC: 80.75% vs WCC: 92.75%) and a wild-type strain (49.75% vs 66.5%). The allele frequencies L1014F, L1014S kdr, and G116S ace -1R mutations conferring resistance, respectively, to pyrethroids and carbamates / organophosphates were 0.95, 0.4 and 0.12. Deltamethrin and lambda-cyhalothrin were identified in the water samples taken in October/November from mosquitoes breeding in the CC growing area. The concentrations obtained were respectively 0.0147ug/L and 1.49 ug/L to deltamethrin and lambdacyhalothrin. Our results provided evidence by direct analysis (biological and chromatographic tests) of the role of agriculture as a source of selection pressure on vectors to insecticides used in growing areas.

Young Scientists Fund of Fujian Academy of Agricultural Sciences 2012DBS-3 YC2015-2 Fujian Science and Technology Agency of China 2015J05062; The whitefly Bemisia tabaci (Gennadius) is an important agricultural insect pest worldwide. The B and Q biotypes are the two most predominant and devastating biotypes prevalent across China. However, there are few studies regarding the occurrence of the Q biotype in Fujian Province, China, where high insecticide resistance has been reported in the B biotype. Differences in some biological characteristics between the B and Q biotypes, especially insecticide resistance, are considered to affect the outcome of their competition. Extensive surveys in Fujian revealed that the B biotype was predominant during 2005-2014, whereas the Q biotype was first detected in some locations in 2013 and widely detected throughout the province in 2014. Resistance to neonicotinoids (that have been used for more than 10 years) exhibited fluctuations in open fields, but showed a continual increasing trend in protected areas. Resistance to lambda-cyhalothrin, chlorpyrifos, and abamectin exhibited a declining trend. Resistance to novel insecticides, such as nitenpyram, pymetrozine, sulfoxaflor, and cyantraniliprole, in 2014 was generally below a moderate level. A decline in insecticide resistance in the B biotype and the rapid buildup of protected crops under global temperature increase may have promoted the establishment of the Q biotype in Fujian.

ARIMNET (ANR-12-AGR001) "APMed" project (Apple and Peach in Mediterranean orchard and by the ONEMA-ECOPHYTO (3ème APR Résistance et Pesticides) "RegPuc" (Quelles strategies d'irrigation et de fertilisation pour réguler les population de pucerons vert en vergers de pêcher) project ARIMNET (ANR-12-AGR001) "APMed" project (Apple and Peach in Mediterranean orchard and by the ONEMA-ECOPHYTO (3ème APR Résistance et Pesticides) "RegPuc" (Quelles strategies d'irrigation et de fertilisation pour réguler les population de pucerons vert en vergers de pêcher) projectARIMNET (ANR-12-AGR001) "APMed" project (Apple and Peach in Mediterranean orchard and by the ONEMA-ECOPHYTO (3ème APR Résistance et Pesticides) "RegPuc" (Quelles strategies d'irrigation et de fertilisation pour réguler les population de pucerons vert en vergers de pêcher) project; Peach green aphid and rosy aphids can develop resistance to insecticides. Alternative strategies are therefore required to control these major pests in commercial orchards. To identify the key plant variables which determine tree resistance and could be manipulated by usual cultural practices we submitted potted peach and apple trees to contrasted water and nitrogen inputs. The trees were then artificially infected and the infestation dynamic followed in line with shoot development and apex composition. The high infested shoots grew faster, developed more secondary ramifications and their apices had higher amino acid and soluble sugar concentrations than the low infested shoots. Moreover, aphids preferred trees having a small number of fast growing shoots to others, having the same number of leaves being distributed among a higher number of smaller shoots. Irrigation and fertilisation could thus be used to improve tree resistance to aphids since those techniques contribute to the control of shoot development and composition.

Field populations of the cotton aphid, Aphis gossypii Glover, are structured into geographically widespread host races. In the cotton-producing regions of West and Central Africa (WCA), two genotypes have been repeatedly detected within the cotton host race, one of which (Burk1) is prevalent (>90%) and resistant to several insecticides, as opposed to the second one (Ivo). Here, we conducted whole plant and field cage experiments to test hypotheses for such low genetic diversity, including selection from insecticide treatments, interclonal competition and adaptation to host plant, or climatic conditions. To assess the genetic diversity of immigrant aphids, alatae were trapped and collected on cotton and relay host plants (okra and roselle) in the early cropping season. Individuals were genotyped at eight specific microsatellite loci and characterized by a multilocus genotype (MLG). When independently transferred from cotton (Gossypium hirustum L.) leaf discs to whole plants (G. hirsutum and G. arboreum, roselle and okra), Ivo and Burk1 performed equally well. When concurrently transferred from cotton leaf discs to the same plant species, Ivo performed better than Burk1, indicating that competition favoured Ivo. This was also the case on G. hirsutum growing outdoors. Conversely, Burk1 prevailed when cotton plants were sprayed with insecticides. In experiments where aphids were allowed to move to neighbouring plants, Burk1 was better represented than Ivo on low-populated plants, suggesting that dispersal may be a way to avoid competition on crowded plants. Most cotton aphids collected on cotton or relay host plants in the early cropping season were Burk1 (>90%), indicating high dispersal ability and, probably reflecting high frequency on host plants from which they dispersed. In the agricultural landscape of WCA, the use of broad-range insecticides on both cotton and relay host plants has led to the prevalence of one genotype of A. gossypii resistant to different classes of insecticides. Deployment of widespread and integrated pest management strategies are needed to restore cotton aphid control.

Resistance to chlorpyriphos insecticide in Bemisia tabaci from a field population collected in Benin, West Africa was suggested with bioassay showing the presence of two sub-populations. Patterns of acetylcholinesterase (AChE) inhibition by the organophosphate chlorpyriphos-oxon were analyzed to estimate the number of possible genotypes with different sensitivity expected in three B. tabaci field populations collected in Benin. The analysis of inhibition patterns in these populations compared with four laboratory strains of B. tabaci using chlorpyriphos-oxon allowed the differentiation of three possible genotypes. In the reference strain SUD-S we detected two different acetylcholinesterases with different sensitivity to chlorpyriphos oxon suggesting the presence of two genes ace 1 and ace 2. The proportion of the insensitive enzyme (ace 2) was estimated to be 31%. In field populations we can detect two alleles at the same gene locus ace 1: one susceptible ace1S and one resistant ace1R. Both strains called Arizona University and Mexico-S2 have lost sensitive ace1S but the field populations from Benin clearly contained at least three genotypes confirming heterogeneous populations not completely resistant.

La culture de plantes transgéniques Bt – produisant des toxines insecticides issues de la bactérie Bacillus thuringiensis – engendre un risque que les populations de ravageurs cibles deviennent résistantes à ces toxines. Pour limiter ce risque, les autorités des États-Unis exigent la mise en oeuvre d’une stratégie appelée « haute dose/refuge » (HDR). Cette stratégie repose sur le maintien, à proximité des cultures transgéniques, de cultures « refuges » – exemptes de toxines Bt – constituant des réservoirs d’individus sensibles. Son efficacité est notamment conditionnée par un brassage génétique intense entre ces individus sensibles et les individus résistants sélectionnés dans les parcelles de plantes Bt. Pour plusieurs ravageurs cibles de ces toxines, sa mise en oeuvre a pourtant précédé l’examen détaillé des traits d’histoires de vie pouvant influencer l’intensité de ce brassage. Des études ont, depuis, partiellement comblé ces manques : nous présentons une synthèse de résultats récents sur la pyrale du maïs, une des cibles principales des maïs Bt. Bien que ce papillon ravageur soit hautement polyphage, les populations se nourrissant d’autres plantes hôtes – sauvages ou cultivées – sont trop minoritaires pour limiter efficacement le développement de résistances. Par ailleurs, une partie des pyrales semble se reproduire à proximité immédiate de leur lieu d’émergence, de sorte que des refuges situés à plusieurs centaines de mètres des maïs Bt – la distance maximale autorisée étant actuellement de 800 mètres – ne garantissent pas le brassage génétique entre individus sensibles et résistants. Dans le cas de rotations culturales, ce brassage pourrait néanmoins être accru par une gestion différente des bordures de champs Bt et conventionnels. Bien qu’aucune résistance ne se soit déclarée 10 ans après la mise en culture des premiers maïs Bt, ces données indiquent que la stratégie HDR telle qu’elle est actuellement appliquée n’est pas forcément optimale et, plus généralement, qu’il est illusoire d’espérer définir une stratégie universellement adaptée, The use of transgenic crops producing toxins from the bacterium Bacillus thuringiensis – or Bt crops – is associated with the risk that the targeted pests become resistant to these toxins. To reduce this risk, the US government required the implementation of a strategy named High Dose/Refuge (HDR). This strategy is based on maintaining Bt toxin-free plants or crops – referred to as « refuges » – to preserve a pool of susceptible insects in the vicinity of Bt fields. Among other factors, its efficiency relies on a high gene flow between these susceptible individuals and any resistant individuals selected in Bt fields. For several pests targeted by these toxins, this strategy was nevertheless implemented when little was in fact know, as to the life history traits likely to influence the intensity of the gene flow. Part of this gap has been filled since then: we summarize here the recent advances on the European corn borer (ECB), one of the main targets of insecticidal Bt maize. Although this moth pest is highly polyphagous, its other host plants – whether wild or cultivated – do not provide a sufficient source of susceptible individuals to efficiently prevent toxin resistance from developing. Moreover, a fraction of the ECB reproduce in close vicinity of their place of emergence, so that refuges situated a few hundred meters from Bt maize fields – the maximal distance currently required is 800 meters – may not warrant a sufficient intermixing between susceptible and resistant individuals. In crop rotation situations, this intermixing could however be facilitated through a contrasted management of herbaceous maize field borders. Although 10 years after the beginning of Bt maize cultivation no resistance has yet broken out, our data suggests that it is illusory to aim at a universally suitable strategy, and that the HDR strategy – as currently implemented – may not necessarily be optimal

Mutations are the origin of the many "variants" present in natural populations. Adaptive variants are propagated by natural selection. However a mutation beneficial for a trait can negatively affect other traits (selective cost): a trade-off thus emerges between the benefits and the costs it induces. This PhD aimed at understanding how environmental changes could affect the evolutionary trade-offs of various types of adaptive mutations (substitutions, heterogeneous duplications, amplifications). In mosquitoes, organophosphate (OPs) and carbamates (CXs) insecticides usage has selected three major adaptive responses: gene amplifications at the Ester locus (encoding detoxifying enzymes), a substitution at the ace-1 locus (encoding the target of the insecticides), and gene duplications pairing susceptible and resistance ace-1 copies. The first axis of my PhD aimed at understanding the role of these heterogeneous duplications (combining two different copies of the same gene) in adaptation. Characterizing their evolutionary trade-offs, we showed that they confer a phenotype similar to standard heterozygotes. However, the study of their worldwide distribution and laboratory analyzes showed that these duplications, advantageous at the heterozygous state, are mostly sublethal when homozygous. The second axis of this PhD was the study of the impact of selection pressure variations on the dynamics of adaptive alleles. An experimental evolution study showed that intermediate selective pressures could generate overdominance situations at the ace-1 locus, promoting the selection of heterogeneous duplications. Furthermore, analyzing Montpellier samples collected over a 27 years period allowed us establishing the quantitative relationship between selective pressure variations and fitness variations for the different Ester resistance alleles. Finally, by studying three different geographical areas (Mayotte and Martinique islands and Montpellier) we showed that the various adaptations were not responding similarly to a major environmental change resulting from the selection pressure withdrawal (OPs and CXs were banned in 2007): while the ace-1 locus resistance alleles tended to disappear, those of the Ester locus remained at a significant frequency in natural populations., Les mutations sont à l'origine des nombreux "variants" présents dans les populations naturelles. Les variants adaptatifs sont propagés par sélection naturelle. Cependant, une mutation bénéfique sur un trait peut affecter négativement d’autres traits (coût sélectif): un compromis émerge alors entre les avantages et les coûts qu’elle induit. Cette thèse vise à comprendre comment des modifications de l’environnement peuvent affecter les compromis évolutifs de différents types de mutations adaptatives (substitutions, duplications hétérogènes, amplifications). Chez les moustiques, l’utilisation d’insecticides organophosphorés (OPs) et carbamates (CXs) a sélectionné trois réponses adaptatives majeures : une amplification de gènes au locus Ester (codant pour des enzymes détoxicantes), une substitution au locus ace-1 (codant pour la cible des insecticides), et des duplications associant une copie sensible et une copie résistante du locus ace-1. Un premier axe de ma thèse a été de mieux comprendre le rôle de ces duplications hétérogènes (qui associent deux copies divergentes d’un même gène) dans l’adaptation. En caractérisant leurs compromis évolutifs nous avons montré qu'elles confèrent un phénotype proche de celui d’hétérozygotes standards. Toutefois, l’étude de leur distribution mondiale et des analyses en laboratoire ont révélé que ces duplications, avantageuses à l’état hétérozygote, sont majoritairement sublétales à l’état homozygote. Le second axe de cette thèse a été l’étude de l’influence des variations de pression de sélection sur la dynamique des allèles adaptatifs. Une étude d’évolution expérimentale a montré que des pressions de sélection intermédiaires pouvaient générer des situations de superdominance au locus ace-1, favorables à la sélection de duplications hétérogènes. Par ailleurs, l’analyse d’échantillons montpelliérains récoltés sur une trentaine d’années nous a permis de relier quantitativement les variations de la pression de sélection et les variations de la valeur sélective des différents allèles du locus Ester. Enfin, l’étude de trois zones géographiques (Mayotte, Martinique, et Montpellier) a permis de montrer que les différentes adaptations ne répondaient pas de la même façon à une modification environnementale majeure liée au retrait de la pression de sélection (interdiction des OPs et CXs en 2007) : alors que les allèles de résistance du locus ace-1 tendent à disparaitre, ceux du locus Ester se maintiennent en fréquence non négligeable dans les populations naturelles.

Mutations are the origin of the many "variants" present in natural populations. Adaptive variants are propagated by natural selection. However a mutation beneficial for a trait can negatively affect other traits (selective cost): a trade-off thus emerges between the benefits and the costs it induces. This PhD aimed at understanding how environmental changes could affect the evolutionary trade-offs of various types of adaptive mutations (substitutions, heterogeneous duplications, amplifications). In mosquitoes, organophosphate (OPs) and carbamates (CXs) insecticides usage has selected three major adaptive responses: gene amplifications at the Ester locus (encoding detoxifying enzymes), a substitution at the ace-1 locus (encoding the target of the insecticides), and gene duplications pairing susceptible and resistance ace-1 copies. The first axis of my PhD aimed at understanding the role of these heterogeneous duplications (combining two different copies of the same gene) in adaptation. Characterizing their evolutionary trade-offs, we showed that they confer a phenotype similar to standard heterozygotes. However, the study of their worldwide distribution and laboratory analyzes showed that these duplications, advantageous at the heterozygous state, are mostly sublethal when homozygous. The second axis of this PhD was the study of the impact of selection pressure variations on the dynamics of adaptive alleles. An experimental evolution study showed that intermediate selective pressures could generate overdominance situations at the ace-1 locus, promoting the selection of heterogeneous duplications. Furthermore, analyzing Montpellier samples collected over a 27 years period allowed us establishing the quantitative relationship between selective pressure variations and fitness variations for the different Ester resistance alleles. Finally, by studying three different geographical areas (Mayotte and Martinique islands and Montpellier) we showed that the various adaptations were not responding similarly to a major environmental change resulting from the selection pressure withdrawal (OPs and CXs were banned in 2007): while the ace-1 locus resistance alleles tended to disappear, those of the Ester locus remained at a significant frequency in natural populations.; Les mutations sont à l'origine des nombreux "variants" présents dans les populations naturelles. Les variants adaptatifs sont propagés par sélection naturelle. Cependant, une mutation bénéfique sur un trait peut affecter négativement d’autres traits (coût sélectif): un compromis émerge alors entre les avantages et les coûts qu’elle induit. Cette thèse vise à comprendre comment des modifications de l’environnement peuvent affecter les compromis évolutifs de différents types de mutations adaptatives (substitutions, duplications hétérogènes, amplifications). Chez les moustiques, l’utilisation d’insecticides organophosphorés (OPs) et carbamates (CXs) a sélectionné trois réponses adaptatives majeures : une amplification de gènes au locus Ester (codant pour des enzymes détoxicantes), une substitution au locus ace-1 (codant pour la cible des insecticides), et des duplications associant une copie sensible et une copie résistante du locus ace-1. Un premier axe de ma thèse a été de mieux comprendre le rôle de ces duplications hétérogènes (qui associent deux copies divergentes d’un même gène) dans l’adaptation. En caractérisant leurs compromis évolutifs nous avons montré qu'elles confèrent un phénotype proche de celui d’hétérozygotes standards. Toutefois, l’étude de leur distribution mondiale et des analyses en laboratoire ont révélé que ces duplications, avantageuses à l’état hétérozygote, sont majoritairement sublétales à l’état homozygote. Le second axe de cette thèse a été l’étude de l’influence des variations de pression de sélection sur la dynamique des allèles adaptatifs. Une étude d’évolution expérimentale a montré que des pressions de sélection intermédiaires pouvaient générer des situations de superdominance au locus ace-1, favorables à la sélection de duplications hétérogènes. Par ailleurs, l’analyse d’échantillons montpelliérains récoltés sur une trentaine d’années nous a permis de relier quantitativement les variations de la pression de sélection et les variations de la valeur sélective des différents allèles du locus Ester. Enfin, l’étude de trois zones géographiques (Mayotte, Martinique, et Montpellier) a permis de montrer que les différentes adaptations ne répondaient pas de la même façon à une modification environnementale majeure liée au retrait de la pression de sélection (interdiction des OPs et CXs en 2007) : alors que les allèles de résistance du locus ace-1 tendent à disparaitre, ceux du locus Ester se maintiennent en fréquence non négligeable dans les populations naturelles.

International audience; BACKGROUNDThe taxonomy of the species complex Bemisia tabaci, a serious agricultural pest worldwide, is not well resolved yet, even though species delimitation is critical for designing effective control strategies. Based on a threshold of 3.5% mitochondrial (mtCOI) sequence divergence, recent studies have identified 28 putative species. Among them, mitochondrial variability associated with particular symbiotic compositions (=cytotypes) can be observed, as in MED, which raises the question of whether it is a single or a complex of biological species.RESULTSUsing microsatellites, an investigation was made of the genetic relatedness of Q1 and ASL cytotypes that belong to MED. Samples of the two cytotypes were collected in West Africa where they live in sympatry on the same hosts. Genotyping revealed a high level of differentiation, without evidence of gene flow. Moreover, they differed highly in frequencies of resistance alleles to insecticides, which were much higher in Q1 than in ASL.CONCLUSIONQ1 and ASL are sufficiently reproductively isolated for the introgression of neutral alleles to be prevented, suggesting that they are actually different species. This indicates that nuclear genetic differentiation must be investigated within groups with less than 3.5% mtCOI divergence in order to elucidate the taxonomy of B. tabaci at a finer level. Overall, these data provide important information for pest management.

Background Culicoides biting midges are biological vectors of internationally important arboviruses of livestock and equines. Insecticides are often employed against Culicoides as a part of vector control measures, but systematic assessments of their efficacy have rarely been attempted. The objective of the present study is to determine baseline susceptibility of multiple Culicoides vector species and populations in Europe and Africa to the most commonly used insecticide active ingredients. Six active ingredients are tested: three that are based on synthetic pyrethroids (alpha-cypermethrin, deltamethrin and permethrin) and three on organophosphates (phoxim, diazinon and chlorpyrifos-methyl). Methods Susceptibility tests were conducted on 29,064 field-collected individuals of Culicoides obsoletus Meigen, Culicoides imicola Kieffer and a laboratory-reared Culicoides nubeculosus Meigen strain using a modified World Health Organization assay. Populations of Culicoides were tested from seven locations in four different countries (France, Spain, Senegal and South Africa) and at least four concentrations of laboratory grade active ingredients were assessed for each population. Results The study revealed that insecticide susceptibility varied at both a species and population level, but that broad conclusions could be drawn regarding the efficacy of active ingredients. Synthetic pyrethroid insecticides were found to inflict greater mortality than organophosphate active ingredients and the colony strain of C. nubeculosus was significantly more susceptible than field populations. Among the synthetic pyrethroids, deltamethrin was found to be the most toxic active ingredient for all species and populations. Conclusions The data presented represent the first parallel and systematic assessment of Culicoides insecticide susceptibility across several countries. As such, they are an important baseline reference to monitor the susceptibility status of Culicoides to current insecticides and also to assess the toxicity of new active ingredients with practical implications for vector control strategies. Electronic supplementary material The online version of this article (doi:10.1186/s13071-015-1042-8) contains supplementary material, which is available to authorized users.

Depuis la mise en évidence de l'implication d'un insecte dans le cycle parasitaire et la dissémination d'une maladie, la lutte contre ces insectes est devenue une alternative pour contrôler les maladies à transmission vectorielle. La peste équine africaine est un exemple de maladie à transmission vectorielle dont l'agent causal, un virus, est transmis aux chevaux par les Culicoides (Diptera : Ceratopogonidae). C'est une maladie endémique au Sénégal (Afrique de l'Ouest) et la dernière épizootie date de 2007 avec la mort de 1 169 chevaux pour un coût total estimé à 1,4 millions d'Euros. En Afrique du Sud, les vecteurs impliqués dans la transmission de la peste équine africaine sont Culicoides imicola et C. bolitinos mais les espèces vectrices au Sénégal n'ont pas encore été déterminées. En outre, la lutte contre les Culicoides vecteurs reste très limitée par le manque de connaissances sur leur bio-écologie et faute de méthodes opérationnelles efficaces. Depuis 2011, plusieurs études ont été menées dans la région des Niayes du Sénégal pour une meilleure connaissance de l'identité des espèces vectrices et de leur bio-écologie afin d'élaborer des stratégies de lutte antivectorielle adaptées au contexte local. Ces études ont permis d'identifier 41 espèces dont 19 espèces nouvelles pour le Sénégal, portant la liste des Culicoides à 53 espèces recensées dans le pays. Parmi ces espèces nouvelles, se trouve C. oxystoma identifiée pour la première fois en région Afro-tropicale et aussi C. bolitinos le second vecteur du virus de la peste équine en Afrique du Sud. Ces travaux ont permis de mettre en évidence C. oxystoma, C. imico la et C. kingi comme les vecteurs potentiels de la peste équine africaine dans les Niayes. Culicoides oxystoma et C. imicola présentent des préférences trophiques orientées sur les chevaux avec des activités de vol crépusculaire et nocturne respectivement, la première espèce pouvant également être active le matin sous certaines conditions favorables de température et d'hygrométrie. Par contre, C. kingi préfère plutôt les bovins mais présente un comportement opportuniste en l'absence des hôtes privilégiés. Ces trois espèces incriminées présentent une sensibilité aux trois matières actives insecticides testées : la deltaméthrine a été le principe actif le plus toxique suivi de la perméthrine et du chlorpyrifos. On note toutefois une sensibilité réduite de C. kingi à la deltaméthrine. Les études préliminaires d'efficacité de produits insecticides (pour-on, moustiquaires imprégnées) que nous avons réalisées sur le terrain n'ont pas été très concluantes et soulignent la nécessité de poursuivre ces investigations dans le futur. D'autres études complémentaires apparaissent indispensables pour explorer au laboratoire la compétence vectorielle des espèces incriminées vis-à-vis du virus de la peste équine et identifier sur le terrain leurs gites larvaires et de repos.

The fall armyworm, Spodoptera frugiperda (J. E. Smith)(Lepidoptera: Noctuidae), is an important agricultural pest of the Western Hemisphere noted for its broad host range, long distance flight capabilities, and a propensity to develop resistance to pesticides that includes a subset of those used in genetically modified corn varieties. These characteristics exacerbate the threat fall armyworm poses to agriculture, with the potential that a resistance trait arising in one geographical location could rapidly disseminate throughout the hemisphere. A region of particular concern is the Caribbean, where a line of islands that extends from Florida to Venezuela provides a potential migratory pathway between populations from North and South America that could allow for consistent and substantial genetic interactions. In this study, surveys of populations from Peru, Bolivia, Paraguay, and Trinidad & Tobago expand on previous work in South America that indicates a generally homogeneous population with respect to haplotype markers. This population differs from that found in most of the Lesser Antilles where a combination of genetic and meteorological observations is described that indicate fall armyworm migration from Puerto Rico to as far south as Barbados, but does not support significant incursion into Trinidad & Tobago and South America. Air transport projections demonstrate that the wind patterns in the Caribbean region are not conducive to consistent flight along the north-south orientation of the Lesser Antilles, supporting the conclusion that such migration is minor and sporadic, providing few opportunities for genetic exchanges. The implications of these findings on the dissemination of deleterious traits between the two Western Hemisphere continents are discussed. Fil: Rodney N. Nagoshi. United States Department Of Agriculture. Center For Medical Agric And Vet Entomology; Estados Unidos Fil: Fleischer, Shelby. The Pennsylvania State University; Estados Unidos Fil: Meagher, Robert L.. United States Department of Agriculture; Estados Unidos Fil: Hay Roe, Mirian. United States Department of Agriculture; Estados Unidos Fil: Khan, Ayub. The University of the West Indies; Trinidad y Tobago Fil: Murúa, María Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Tecnología Agroindustrial del Noroeste Argentino. Provincia de Tucumán. Ministerio de Desarrollo Productivo. Estación Experimental Agroindustrial ; Argentina Fil: Silvie, Pierre. Universite de Paris; Francia Fil: Vergara, Clorinda. Universidad Agraria La Molina; Perú Fil: Westbrook, John. United States Department of Agriculture; Estados Unidos

SUMMARYBluetongue is a disease of major economic concern in Europe. Its causative agent, bluetongue virus (BTV), is transmitted by several Culicoides species (mainly Culicoides imicola and Culicoides obsoletus in Europe). The application of insecticides on animals may reduce transmission of BTV, however, no formulation is currently licensed specifically against Culicoides midges. The present study assesses the susceptibility of C. obsoletus to deltamethrin using an adapted World Health Organization (WHO) susceptibility test. Midges were exposed to different dosages of deltamethrin for 1 h, and mortality after 1 h and 24 h was recorded. Results indicated that deltamethrin is highly toxic to C. obsoletus since a dose of 1·33×10−4% was enough to kill 50% of the population (LD50) in 24 h. The deltamethrin concentration needed to kill 90% of the population (LD90) was 5·55×10−4%. The results obtained in the present work could help to create a system that can be used to assess insecticide resistance and susceptibility of Culicoides biting midges.

Les Culicoides sont des petits insectes hématophages vecteurs d'arbovirus responsables d'importantes pertes économiques au niveau mondial dans l'industrie agroalimentaire incluant le virus de la fièvre catarrhale ovine et le virus de Schmallenberg. Afin de réduire le contact entre les Culicoides et leur hôte, plusieurs moyens de lutte peuvent être utilisés comme la lutte écologique (modification des habitats larvaires), la lutte biologique (introduction d'un ennemi naturel dans leur environnement), la lutte mécanique (confinement des animaux dans des bâtiments) et la lutte chimique (utilisation d'insecticides). Cette dernière, restant la plus utilisée en Europe, est recommandée par les autorités sanitaires pour réduire la transmission de la maladie, ainsi que la vaccination et la restriction de mouvements des animaux pendant les périodes critiques de circulation du virus. L'utilisation de produits insecticides reste le premier recours en absence de vaccin efficace contre les nouveaux virus et les différentes souches circulantes. Néanmoins, leur efficacité est incertaine et variable selon les études menées jusqu'à présent, visant leur évaluation. Ce travail de thèse tend à améliorer les connaissances sur les méthodes de lutte antivectorielle disponibles contre les Culicoides européens vecteurs de virus émergents d'intérêt en santé animale et de proposer des procédures standardisées qui nous ont permis d'obtenir des valeurs de références, inexistantes jusqu'à présent, mais indispensables dans la lutte antivectorielle contre les Culicoides.

International audience; The tobacco aphid Myzus persicae nicotianae Blackman is a subspecies of the highly polyphagous and agricultural pest Myzus persicae (Sulzer). For its control, insecticide applications are widely used, but resistance to numerous molecules has been reported, displaying at least three insecticide resistance mechanisms, including: (i) elevated carboxylesterases (E-Carb), (ii) modification of the acetylcholinesterase (MACE), and (iii) kdr and super-kdr insensitivity mutations. In Chile, populations of the tobacco aphid are characterized by the presence of a single predominant clone, which is also present in high proportions in other countries of the Americas. This aphid clone exhibits low levels of carboxylesterase activity and is kdr susceptible, but the MACE mechanism of insecticide resistance has not been studied. In order to characterize the tobacco aphid in terms of the MACE mechanism and to identify a preliminary group of aphid genes putatively involved in insecticide resistance, a cDNA microarray was used to study the transcriptomic responses when aphids are sprayed with a carbamate insecticide. The single Chilean clone of the tobacco aphid was characterized as MACE susceptible, but we found 38 transcripts significantly regulated by insecticide exposure (13 up- and 25 down-regulated genes). The expression of six of them was validated by qRT-PCR experiments at several time points (6, 12, 18, 24, 30, 36, and 42 h) after insecticide application. This mutational and transcriptomic characterization of the tobacco aphid responding to insecticide spray opens new hypotheses in the understanding of the molecular mechanisms underlying insecticide resistance.

Pyrethroid insecticides induce an excito-repellent effect that reduces contact between humans and mosquitoes. Insecticide use is expected to lower the risk of pathogen transmission, particularly when impregnated on long-lasting treated bednets. When applied at low doses, pyrethroids have a toxic effect, however the development of pyrethroid resistance in several mosquito species may jeopardize these beneficial effects. The need to find additional compounds, either to kill disease-carrying mosquitoes or to prevent mosquito contact with humans, therefore arises. In laboratory conditions, the effects (i. e., repellent, irritant and toxic) of 20 plant extracts, mainly essential oils, were assessed on adults of Anopheles gambiae, a primary vector of malaria. Their effects were compared to those of DEET and permethrin, used as positive controls. Most plant extracts had irritant, repellent and/or toxic effects on An. gambiae adults. The most promising extracts, i. e. those combining the three types of effects, were from Cymbopogon winterianus, Cinnamomum zeylanicum and Thymus vulgaris. The irritant, repellent and toxic effects occurred apparently independently of each other, and the behavioural response of adult An. gambiae was significantly influenced by the concentration of the plant extracts. Mechanisms underlying repellency might, therefore, differ from those underlying irritancy and toxicity. The utility of the efficient plant extracts for vector control as an alternative to pyrethroids may thus be envisaged.

Une équipe de l’Inra de rennes présente la première encyclopédie numérique sur les pucerons, une référence pour les scientifiques, les professionnels agricoles, les enseignants et leurs étudiants.

Publication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699; International audience; We used eight microsatellite loci and a set of 20 aphid samples to investigate the spatial and temporal genetic structure of rosy apple aphid populations from 13 apple orchards situated in four different regions in France. Genetic variability was very similar between orchard populations and between winged populations collected before sexual reproduction in the fall and populations collected from colonies in the spring. A very small proportion of individuals (similar to 2%) had identical multilocus genotypes. Genetic differentiation between orchards was low (F(ST)

International audience; BACKGROUND: Resistance to the pyrethroid insecticide deltamethrin has been a growing problem in the management of Helicoverpa armigera (Hübner) pest populations in West Africa. Detoxification by P450 enzymes appears to be a major mechanism of resistance, but the genes responsible for resistance are unknown. RESULTS: First, it was shown that deltamethrin resistance in strains from Burkina Faso (Kaya) and from Spain (Seville) were suppressible by piperonyl butoxide and by trichlorophenyl propynyl ether, thus indicating a major role of P450 enzyme(s) in resistance. The larval expression of 21 CYP genes encoding P450 enzymes from six CYP families were then compared by quantitative RT-PCR. Five genes, CYP4L5, CYP4L11, CYP6AE11, CYP332A1 and CYP9A14, were significantly overexpressed in the Kaya and Seville strains when compared with Heliar, a susceptible strain. Significant overexpression of multiple CYP genes (CYP4M6, CYP4M7, CYP6AE11, CYP9A12, CYP332A1 and CYP337B1) was also found in six field strains with different levels of resistance from Benin, Burkina Faso and Mali. CONCLUSION: Although functional or genetic evidence for the role of these P450s in resistance remains to be formally established, results suggest that multiple P450 enzymes contribute to deltamethrin resistance. This study is a first step towards the development of molecular tools for the detection of P450-based resistance in H. armigera. Copyright © 2010 Society of Chemical Industry

Mosquito control represents a major public health concern, as mosquitoes transmit many severe human diseases. After the massive use of chemical insecticides since the fifties, the bacterio-insecticide Bacillus thuringiensis subsp. israelensis (Bti) represents a safe alternative and is now widely used to control mosquito populations. High toxicity due to commercial Bti proliferation and persistence was found in decaying leaf litter collected in mosquito breeding sites. In order to evaluate the evolution of resistance, a laboratory Aedes aegypti strain was selected with field-collected leaf litter containing Bti toxins. Resistance of Aedes aegypti to Bti Cry toxins evolved after only few generations of larval selection. Several approaches were used to study the genetic bases of Bti resistance in the resistant strain. First, the genetic comparison by two genome scans (one with markers linked to transposable elements and one with neutral AFLP markers) of the sensible and the resistant strains revealed genetic loci related to this resistance. Those loci were sequenced and located in the Ae. aegypti genome and allowed the detection of several genomic regions under selection. Then, a transcriptome scan allowed the comparison of the transcription of more than 6000 between the susceptible and the resistant strain. Several genes potentially involved in Bti resistance were detected by combining these results with a candidate gene approach. Among them, a cadherin gene displayed patterns of nucleotide polymorphisms consistent with the action of positive selection and appeared a good candidate for Bti resistance. Furthermore, signatures of selection linked to Bti treatment and high gene flow were detected by a population genomic approach in the Rhône-Alpine mosquito strain Aedes rusticus. Information about genetic factors linked to Bti resistance and biological factors linked to treated species are essential to use adapted resistance management strategies., La résistance aux insecticides chez les moustiques pose des problèmes de santé publique car ils sont vecteurs de nombreuses maladies. Une alternative aux insecticides chimiques est l'utilisation du bactério-insecticide Bacillus thuringiensis subsp israelensis (Bti) qui a l'avantage de produire un mélange de six toxines spécifiques des Diptères. Cependant le Bti commercial peut proliférer et s'accumuler, entrainant une forte toxicité dans les litières végétales de certains gîtes à moustiques. Afin d'étudier l'évolution de la résistance au Bti chez les moustiques, j'ai sélectionné en laboratoire une souche d'Aedes aegypti avec des litières végétales contenant des toxines de Bti. Une résistance multigénique aux toxines Cry du Bti est apparue en seulement quelques générations chez la souche sélectionnée. Plusieurs approches ont été utilisées pour rechercher les bases génétiques de la résistance au Bti chez la souche d'Ae. aegypti résistante. Deux "scans génomiques" ont permis de déterminer plusieurs régions du génome présentant des signatures de sélection. Ensuite, les niveaux de transcription de plus de 6000 gènes ont été étudiés par séquençage haut débit. La combinaison de ces résultats avec une approche "gènes candidats" a permis d'obtenir une liste de gènes potentiellement liés à la résistance au Bti. Parmi les gènes identifiés, un gène codant pour une cadhérine présente des signatures de sélection chez la souche résistante et semble donc impliqué dans la résistance au Bti. De plus, une étude de génomique des populations de l'espèce de terrain Aedes rusticus traitée depuis 20 ans au Bti a mis en évidence des signatures de sélection liées au traitement et des flux de gènes importants chez cette espèce dans la région Rhône-Alpes. La caractérisation de facteurs génétiques liés à la résistance et de facteurs biologiques liés aux espèces traitées peut aider à la mise en place de stratégies de gestion limitant l'évolution de la résistance au Bti dans ces populations.

Mosquito control represents a major public health concern, as mosquitoes transmit many severe human diseases. After the massive use of chemical insecticides since the fifties, the bacterio-insecticide Bacillus thuringiensis subsp. israelensis (Bti) represents a safe alternative and is now widely used to control mosquito populations. High toxicity due to commercial Bti proliferation and persistence was found in decaying leaf litter collected in mosquito breeding sites. In order to evaluate the evolution of resistance, a laboratory Aedes aegypti strain was selected with field-collected leaf litter containing Bti toxins. Resistance of Aedes aegypti to Bti Cry toxins evolved after only few generations of larval selection. Several approaches were used to study the genetic bases of Bti resistance in the resistant strain. First, the genetic comparison by two genome scans (one with markers linked to transposable elements and one with neutral AFLP markers) of the sensible and the resistant strains revealed genetic loci related to this resistance. Those loci were sequenced and located in the Ae. aegypti genome and allowed the detection of several genomic regions under selection. Then, a transcriptome scan allowed the comparison of the transcription of more than 6000 between the susceptible and the resistant strain. Several genes potentially involved in Bti resistance were detected by combining these results with a candidate gene approach. Among them, a cadherin gene displayed patterns of nucleotide polymorphisms consistent with the action of positive selection and appeared a good candidate for Bti resistance. Furthermore, signatures of selection linked to Bti treatment and high gene flow were detected by a population genomic approach in the Rhône-Alpine mosquito strain Aedes rusticus. Information about genetic factors linked to Bti resistance and biological factors linked to treated species are essential to use adapted resistance management strategies.; La résistance aux insecticides chez les moustiques pose des problèmes de santé publique car ils sont vecteurs de nombreuses maladies. Une alternative aux insecticides chimiques est l'utilisation du bactério-insecticide Bacillus thuringiensis subsp israelensis (Bti) qui a l'avantage de produire un mélange de six toxines spécifiques des Diptères. Cependant le Bti commercial peut proliférer et s'accumuler, entrainant une forte toxicité dans les litières végétales de certains gîtes à moustiques. Afin d'étudier l'évolution de la résistance au Bti chez les moustiques, j'ai sélectionné en laboratoire une souche d'Aedes aegypti avec des litières végétales contenant des toxines de Bti. Une résistance multigénique aux toxines Cry du Bti est apparue en seulement quelques générations chez la souche sélectionnée. Plusieurs approches ont été utilisées pour rechercher les bases génétiques de la résistance au Bti chez la souche d'Ae. aegypti résistante. Deux "scans génomiques" ont permis de déterminer plusieurs régions du génome présentant des signatures de sélection. Ensuite, les niveaux de transcription de plus de 6000 gènes ont été étudiés par séquençage haut débit. La combinaison de ces résultats avec une approche "gènes candidats" a permis d'obtenir une liste de gènes potentiellement liés à la résistance au Bti. Parmi les gènes identifiés, un gène codant pour une cadhérine présente des signatures de sélection chez la souche résistante et semble donc impliqué dans la résistance au Bti. De plus, une étude de génomique des populations de l'espèce de terrain Aedes rusticus traitée depuis 20 ans au Bti a mis en évidence des signatures de sélection liées au traitement et des flux de gènes importants chez cette espèce dans la région Rhône-Alpes. La caractérisation de facteurs génétiques liés à la résistance et de facteurs biologiques liés aux espèces traitées peut aider à la mise en place de stratégies de gestion limitant l'évolution de la résistance au Bti dans ces populations.

Resistance of arthropods to organophosphates and carbamates used as insecticides is mainly due to mutations in genes encoding carboxylesterase or acetylcholinesterase members of the alpha/beta-hydrolase fold superfamily of proteins. Mutations that have been described at the molecular level concern 24 species, 31 genes and 32 identical positions in the aligned aminoacid sequences. Seven of these positions are found in more than four species and can be considered as hot spots for mutations. Mutations in one single gene also result in cross resistance to pyrethroids. These figures along with all pieces of information related to these mutations can be recovered from the ESTHER database, dedicated to the alpha/beta-hydrolase fold superfamily (http://bioweb.ensam.inra.fr/ esther), through built-in or custom made queries. A sequence alignment of enzymes involved in resistance with highlighted mutated amino acid residues is provided. Selecting one amino acid residue leads to all information about mutations analyzed at this position. Links to the related literature are also available. © Pesticide Science Society of Japan

In a integrated pest management control, the Entente Interdépartementale pour la Démoustication (EID Ain, Isere, Rhone, Savoie Rhone-Alps used Bti as a biological controlto control mosquito populations. The subject of the present thesis is the result of research collaboration during 40 years between EID and our laboratory research. This agency management uses Bti for 20 years. To date, no mosquito population has appeared resistant to Bti. But previous studies have suggested that there was a difference in sensitivity of mosquito larvae insecticides according to their breeding sites, with differences between herbaceous and arboreal surroundings. We are interested in resistance mechanisms of mosquito larvae. We focused on resistance to various xenobiotics food: temephos (organophosphate insecticide) to Bacillus thuringiensis var. israelensis (Bti - bacteriological insecticide) through the natural litter derived from the decomposition of leaves. From a fundamental point of view, knowledge and understanding of the resistance (of the enzymes involved with environmental factors through the genes involved) stimulated my research. And an applied perspective was to develop to finally imagine an effective non-pollutant system of control which passes through the comprehensive understanding of resistance. The experimental approach is to identify mechanisms in the environmental field, analyzed in the laboratory on a model species (Aedes aegypti here) the mechanisms behind these disturbances, and then return to the field to confront the results of laboratory with those obtained in natura on local species (here Ochlerotatus cataphylla, Aedes rusticus). Thus, this study will focus both on land species (Aedes rusticus, cataphylla Ochlerotatus, Culex pipiens ...) and on laboratory species (Aedes aegypti, Aedes albopictus). To understand the resistance mechanisms brought into play by interfering, we worked on several levels with ecotoxicological studies conducted through field studies, biochemical studies allowing us to characterize the enzymes involved in resistance, and genetic and molecular studies to further investigate these mechanisms, hoping to find some involved genes.; Dans un contexte de lutte intégrée contre les moustiques, l'Entente Interdépartementale pour la Démoustication (E.I.D. Ain, Isère, Rhône, Savoie Rhône-Alpes s'est tournée vers une lutte totalement biologique (Bti) pour lutter contre les moustiques. Mon sujet de thèse s'inscrit dans la suite d'une collaboration scientifique constante depuis 40 ans entre l'E.I.D. et le laboratoire de recherche dans lequel j'ai effectué ma thèse. Cet organisme de gestion utilise le Bti depuis 20 ans. Et bien qu'à ce jour, aucune population de moustique ne soit apparue résistante au Bti, ce gestionnaire s'interroge sur la possibilité d'apparition de populations résistantes aux traitements insecticides. Des travaux antérieurs ont laissé supposer qu'il existait une différence de sensibilité des larves de moustiques aux insecticides en fonction de leur gîte d'origine, les larves originaires de gîtes herbacées étant moins tolérantes que celles provenant des gîtes arborescents. Il nous a semblé nécessaire de comprendre et ainsi de s'intéresser aux différents mécanismes de résistance des larves de moustiques pour permettre, demain, une lutte plus efficace contre cet insecte. Et nous nous intéresserons à la résistance à divers xénobiotiques alimentaires : du téméphos (insecticide organophosphoré) au Bacillus thuringiensis var. israelensis (Bti - bactério-insecticide) en passant par de la litière naturelle issue de la décomposition de feuilles dans les gîtes à moustiques se révélant toxique pour les larves. L'intérêt de cette thèse est double. D'un point de vue fondamental, la connaissance et la compréhension de la résistance (des enzymes impliquées aux facteurs environnementaux en passant par les gènes mis en jeu) stimulent mes recherches. Et d'un point de vue appliqué, il est nécessaire de mettre au point, enfin, un système de lutte efficace non polluant, qui passe par la compréhension globale des résistances. La démarche expérimentale utilisée dans ce travail est d'identifier les dysfonctionnements environnementaux sur le terrain, les analyser au laboratoire sur des espèces modèles (ici Aedes aegypti) les mécanismes à l'origine de ces perturbations, puis revenir sur le terrain pour confronter les résultats de laboratoire avec ceux obtenus in natura (ici Ochlerotatus cataphylla, Aedes rusticus). Ainsi cette étude va porter à la fois sur des espèces de terrain (Aedes rusticus, Ochlerotatus cataphylla, Culex pipiens ...) que sur des espèces de laboratoires (Aedes aegypti, Aedes albopictus ...). Pour comprendre les mécanismes de résistance mis en jeu par ce nuisant, nous avons travaillés à plusieurs niveaux d'études avec des études écotoxicologiques réalisées grâce à des études de terrain en collaboration avec l'E.I.D. (Entente Interdépartementale pour la Démoustication), des études biochimiques nous permettant de caractériser les enzymes de résistance mises en jeu, et des études génétiques et moléculaires pour approfondir ces mécanismes, en espérant trouver les gènes impliqués.

In a integrated pest management control, the Entente Interdépartementale pour la Démoustication (EID Ain, Isere, Rhone, Savoie Rhone-Alps used Bti as a biological controlto control mosquito populations. The subject of the present thesis is the result of research collaboration during 40 years between EID and our laboratory research. This agency management uses Bti for 20 years. To date, no mosquito population has appeared resistant to Bti. But previous studies have suggested that there was a difference in sensitivity of mosquito larvae insecticides according to their breeding sites, with differences between herbaceous and arboreal surroundings. We are interested in resistance mechanisms of mosquito larvae. We focused on resistance to various xenobiotics food: temephos (organophosphate insecticide) to Bacillus thuringiensis var. israelensis (Bti - bacteriological insecticide) through the natural litter derived from the decomposition of leaves. From a fundamental point of view, knowledge and understanding of the resistance (of the enzymes involved with environmental factors through the genes involved) stimulated my research. And an applied perspective was to develop to finally imagine an effective non-pollutant system of control which passes through the comprehensive understanding of resistance. The experimental approach is to identify mechanisms in the environmental field, analyzed in the laboratory on a model species (Aedes aegypti here) the mechanisms behind these disturbances, and then return to the field to confront the results of laboratory with those obtained in natura on local species (here Ochlerotatus cataphylla, Aedes rusticus). Thus, this study will focus both on land species (Aedes rusticus, cataphylla Ochlerotatus, Culex pipiens ...) and on laboratory species (Aedes aegypti, Aedes albopictus). To understand the resistance mechanisms brought into play by interfering, we worked on several levels with ecotoxicological studies conducted through field studies, biochemical studies allowing us to characterize the enzymes involved in resistance, and genetic and molecular studies to further investigate these mechanisms, hoping to find some involved genes.; Dans un contexte de lutte intégrée contre les moustiques, l'Entente Interdépartementale pour la Démoustication (E.I.D. Ain, Isère, Rhône, Savoie Rhône-Alpes s'est tournée vers une lutte totalement biologique (Bti) pour lutter contre les moustiques. Mon sujet de thèse s'inscrit dans la suite d'une collaboration scientifique constante depuis 40 ans entre l'E.I.D. et le laboratoire de recherche dans lequel j'ai effectué ma thèse. Cet organisme de gestion utilise le Bti depuis 20 ans. Et bien qu'à ce jour, aucune population de moustique ne soit apparue résistante au Bti, ce gestionnaire s'interroge sur la possibilité d'apparition de populations résistantes aux traitements insecticides. Des travaux antérieurs ont laissé supposer qu'il existait une différence de sensibilité des larves de moustiques aux insecticides en fonction de leur gîte d'origine, les larves originaires de gîtes herbacées étant moins tolérantes que celles provenant des gîtes arborescents. Il nous a semblé nécessaire de comprendre et ainsi de s'intéresser aux différents mécanismes de résistance des larves de moustiques pour permettre, demain, une lutte plus efficace contre cet insecte. Et nous nous intéresserons à la résistance à divers xénobiotiques alimentaires : du téméphos (insecticide organophosphoré) au Bacillus thuringiensis var. israelensis (Bti - bactério-insecticide) en passant par de la litière naturelle issue de la décomposition de feuilles dans les gîtes à moustiques se révélant toxique pour les larves. L'intérêt de cette thèse est double. D'un point de vue fondamental, la connaissance et la compréhension de la résistance (des enzymes impliquées aux facteurs environnementaux en passant par les gènes mis en jeu) stimulent mes recherches. Et d'un point de vue appliqué, il est nécessaire de mettre au point, enfin, un système de lutte efficace non polluant, qui passe par la compréhension globale des résistances. La démarche expérimentale utilisée dans ce travail est d'identifier les dysfonctionnements environnementaux sur le terrain, les analyser au laboratoire sur des espèces modèles (ici Aedes aegypti) les mécanismes à l'origine de ces perturbations, puis revenir sur le terrain pour confronter les résultats de laboratoire avec ceux obtenus in natura (ici Ochlerotatus cataphylla, Aedes rusticus). Ainsi cette étude va porter à la fois sur des espèces de terrain (Aedes rusticus, Ochlerotatus cataphylla, Culex pipiens ...) que sur des espèces de laboratoires (Aedes aegypti, Aedes albopictus ...). Pour comprendre les mécanismes de résistance mis en jeu par ce nuisant, nous avons travaillés à plusieurs niveaux d'études avec des études écotoxicologiques réalisées grâce à des études de terrain en collaboration avec l'E.I.D. (Entente Interdépartementale pour la Démoustication), des études biochimiques nous permettant de caractériser les enzymes de résistance mises en jeu, et des études génétiques et moléculaires pour approfondir ces mécanismes, en espérant trouver les gènes impliqués.

Les cotonniers Bt exprimant la toxine CryIAc qui ont été commercialisés en Chine depuis 1996 proviennent de variétés locales et américaines. Ceux cultivés en Inde depuis 2002 proviennent d'hybrides locaux introgressant l'événement de transformation Monsanto. Dans ces deux pays, les surfaces en coton Bt ont atteint en 2004 respectivement 66 % et 10 % des surfaces cotonnières. Le niveau d'expression de la toxine est très variable selon les variétés et selon les parties de la plante, si bien qu'au cours du cycle de développement, sa concentration dans les principaux organes du cotonnier n'atteint pas toujours les 1,8 ppm requis pour un contrôle efficace de la chenille Helicoverpa armigera, alors que l'efficacité est généralement correcte vis-à-vis de la chenille épineuse Earias spp. et du ver rose Pectinophora gossypiella. Avec l'introduction du coton Bt, les traitements insecticides dirigés contre les chenilles ont été réduits de 50 à 80 % en Chine et de 40 à 60 % en Inde. Les augmentations de rendement ont été faibles en Chine (moins de 15 %), et dans bien des cas, de nombreux traitements insecticides sont encore effectués contre les autres ravageurs. Dans l'expérience indienne, les augmentations de rendement ont été supérieures (autour de 40 % en moyenne). Les profits ont augmenté de US $ 800/ha en 2004 en Chine et de US $ 477/ha en Inde en 2003. Les études sur les effets non intentionnels sur les organismes non-cibles menées en Chine ont montré de faibles impacts sur l'environnement mais laissent entendre une réduction des populations des ennemis des chenilles de la capsule, au profit d'auxiliaires plus généralistes. À l'heure actuelle, aucune résistance au coton Bt n'a été décelée au champ. Il apparaît que la modification de la cible est le mécanisme majeur de la résistance en Chine et que les gènes de résistance sont présents à un taux supérieur à 1 pour 1000 dans les populations de chenilles d'H. armigera dans les deux pays. La modélisation suggère que l'obtention d'une forte mortalité (via des insecticides appropriés) chez les individus survivants serait la technique la plus efficace de prévention de la résistance.

Cydia pomonella L., la principal plaga de pomáceas y nogales en Chile, ha sido controlada casi exclusivamente con aplicaciones de insecticidas organofosforados. Sin embargo, durante las últimas temporadas se han observado crecientes niveles de frutos dañados a cosecha. Dado que esta plaga ha desarrollado resistencia a insecticidas en varios países, se evaluó la susceptibilidad a dosis diagnóstico de azinfos metil y tebufenozide de larvas diapausantes provenientes de tres huertos de manzano de la Región del Maule y una cepa susceptible de referencia (S); además de la actividad de enzimas detoxificadoras en adultos emergidos de las mismas Tanto la actividad de oxidasas de función múltiple (OFM) como de glutation-S-transferasas (GST) se evaluó a través de fluorimetría, mientras la de esterasas (EST) se determinó por absorbancia. La mortalidad larvaria frente a azinfos metil fue significativamente menor para Molina y Teno (30 y 85,4%, respectivamente) que para la cepa S (95,3%). Para tebufenozide la mortalidad larvaria fue significativamente menor en Molina (35,31%) que en la cepa S (88,6%). La actividad de GST fue significativamente mayor en dos de los tres huertos analizados (Teno = 13.679 unidades de fluorescencia insecto-1 y Molina =13.096 unidades de fluorescencia insecto-1). Similarmente, la actividad de OFM fue significativamente mayor en los mismos huertos, con valores 25,08 y 17,95 picogramos (pg) de 7OH insecto-1 min.-1 para Molina y Teno, respectivamente. La cepa S presentó una actividad de EST significativamente mayor que la de las otras poblaciones, la cual parece no estar relacionada con la menor susceptibilidad a los insecticidas evaluados. Cydia pomonella L., the major pest of pome fruits and walnuts in Chile, has been controlled almost exclusively with applications of organophosphates insecticides. However, during the last few seasons, increasing levels of fruit damage at harvest have been observed. Given that this insect has evolved insecticide resistance in several countries, the susceptibility to diagnostic dosages of azinphos methyl and tebufenozide were evaluated on diapausing larvae in populations from three apple orchards in Maule Region and one susceptible laboratory strain (S); as well as the activity of detoxifying enzymes on adults emerging from the aforementioned. Both mixed function oxidases (OFM) and glutathione-S-tranferases (GST) activities were evaluated by fluorometry, while esterase activity (EST) was determined by absorption. Larval mortality for azinphosmethyl was significantly lower in the populations from Molina and Teno (30 and 85.4%, respectively) than in the susceptible laboratory strain (95.3%). For tebufenozide larval mortality was significantly lower in the Molina strain (35.1%) than the S strain (88.6%). GST activity was statistically higher in two of the three analyzed orchards (13,679 fluorescence insect-1 units in Teno, and 13,096 fluorescence insect-1 units in Molina). Similarly, OFM activity was significantly higher in the same orchards, with values of 25.08 and 17.95 picograms (pg) of 7OH insect-1 min¹ inMolina and Teno, respectively. The S strain had significantly higher EST activity in relation to the other populations, which seems to be unrelated with lower susceptibility to the insecticides evaluated.

International audience; Adaptive changes in populations encountering a new environment are often constrained by deleterious pleiotropic interactions with ancestral physiological functions. Evolutionary responses of populations can thus be limited by natural selection under fluctuating environmental conditions, if the adaptive mutations are associated with pleiotropic fitness costs. In this context, we have followed the evolution of the frequencies of insecticide-resistant mutants of Cydia pomonella when reintroduced into an untreated environment. The novel set of selective forces after removal of insecticide pressure led to the decline of the frequencies of resistant phenotypes over time, suggesting that the insecticideadapted genetic variants were selected against the absence of insecticide (with a selective coefficient estimated at 0.11). The selective coefficients were also estimated for both the major cytochrome P450-dependent monooxygenase (MFO) and the minor glutathione S-transferase (GST) systems (0.17 and negligible, respectively), which have been previously shown to be involved in resistance. The involvement of metabolic systems acting both through xenobiotic detoxification and biosynthetic pathways of endogenous compounds may be central to explaining the deleterious physiological consequences resulting from pleiotropy of adaptive changes. The estimation of the magnitude of the fitness cost associated with insecticide resistance in C. pomonella suggests that resistance management strategies exclusively based on insecticide alternations would be unlikely to delay such a selection process

The diamondback moth Prutella xylostella (L.) (Lepidoptera: Plutellidae) is present in most continents. Control of this pest costs one billion Euros per year worldwide. It is a resistant to most insecticides and even to Bacillus thuringiensis (Berliner) and biological control is a strategy to be considered.[br/] trichogramma (Hymenoptera: trichogrammatidae) present some obvious advantages for use in biological control. These egg parasitoids can easily be reared on a facilitious host and are found naturally on P. xylostella (Tabone et al, 2000).

La teigne du chou (P. xylostella), un des principaux ravageurs des Brassicacées cultivées en France, résiste aux insecticides et même à Bacillus thurengiensis.[br/] Une protection biologique à l' aide de trichogrammes permettrait de résoudre le problème.[br/] Différentes souches, indigènes et exotiques, sont testées en laboratoire et sur le terrain.[br/] Les premiers résultats sont encourageants.

De nombreuses observations, dans beaucoup de régions du monde, ont permis de déceler des accroissements considérables des populations de mouches domestiques dans des localités traitées par des pulvérisations de dieldrine, hydrocarbure chlore a effet prolongé. Cette multiplication fâcheuse d'insectes nuisibles a gêné le déroulement des campagnes antipaludiques. II a donc paru très utile d'entreprendre, dans des conditions contrôlées, une étude visant à déterminer s'il s'agit bien d'une augmentation du potentiel biotique des mouches domestiques a la suite de leur contact avec la dieldrine et de l'apparition ultérieure d'une résistance a ce produit, et non pas d'une multiplication due a quelqu'autre facteur, par exemple à la destruction, par les pulvérisations des prédateurs de la mouche domestique qui seraient sensibles a la dieldrine. On a donc cherché à déceler la possibilité d'une augmentation de la fertilité ou de la vie moyenne des mouches femelles après l'apparition d'une résistance a la dieldrine, en etudiant sur le terrain et en laboratoire plusieurs souches capturées en diverses régions du Liberia, ainsi que des mouches provenant du Sierra Leone et du Nigeria. On a pour cela examiné plusieurs souches sensibles a la dieldrine en soumettant une fraction de chacune à une dose critique de cet insecticide et on a sélectionné ainsi un certain nombre d'insectes résistants. On a alors comparé le potentiel biotique de la souche mère, de la souche secondaire sélectionnée née des insectes qui avaient survécu a l'exposition a la dieldrine, et des souches secondaires non sélectionnées ; cette comparaison a porté sur la fertilité, mesurée par le nombre d'œufs pondus par des groupes de 50 femelles de chaque souche secondaire, et sur la durée de vie totale des groupes. L'analyse statistique des résultats a montré que pour les souches soumise à l'épreuve: a) il y avait une augmentation significative du nombre d'œufs pondus par la première génération issue des mouches sélectionnées pour leur résistance a la dieldrine, par rapport à la ponte des souches secondaires non sélectionnées. b) Cette augmentation n'est pas due à une prolongation de la durée de vie des souches secondaires sélectionnées, mais représente un accroissement absolu du nombre d'œufs pondus. c) L'augmentation de la fertilité est temporaire et disparait a la deuxième ou troisième génération après la sélection, bien que la résistance a la dieldrine reste forte. L'article expose diverses conjectures sur les causes possibles de l'augmentation du potentiel biotique.

Correspondance: bourguet@supagro.inra.fr; National audience; The use of transgenic crops producing toxins from the bacterium Bacillus thuringiensis – or Bt crops – is associated with the risk that the targeted pests become resistant to these toxins. To reduce this risk, the US government required the implementation of a strategy named High Dose/Refuge (HDR). This strategy is based on maintaining Bt toxin-free plants or crops – referred to as « refuges » – to preserve a pool of susceptible insects in the vicinity of Bt fields. Among other factors, its efficiency relies on a high gene flow between these susceptible individuals and any resistant individuals selected in Bt fields. For several pests targeted by these toxins, this strategy was nevertheless implemented when little was in fact know, as to the life history traits likely to influence the intensity of the gene flow. Part of this gap has been filled since then: we summarize here the recent advances on the European corn borer (ECB), one of the main targets of insecticidal Bt maize. Although this moth pest is highly polyphagous, its other host plants – whether wild or cultivated – do not provide a sufficient source of susceptible individuals to efficiently prevent toxin resistance from developing. Moreover, a fraction of the ECB reproduce in close vicinity of their place of emergence, so that refuges situated a few hundred meters from Bt maize fields – the maximal distance currently required is 800 meters – may not warrant a sufficient intermixing between susceptible and resistant individuals. In crop rotation situations, this intermixing could however be facilitated through a contrasted management of herbaceous maize field borders. Although 10 years after the beginning of Bt maize cultivation no resistance has yet broken out, our data suggests that it is illusory to aim at a universally suitable strategy, and that the HDR strategy – as currently implemented – may not necessarily be optimal; La culture de plantes transgéniques Bt – produisant des toxines insecticides issues de la bactérie Bacillus thuringiensis – engendre un risque que les populations de ravageurs cibles deviennent résistantes à ces toxines. Pour limiter ce risque, les autorités des États-Unis exigent la mise en oeuvre d’une stratégie appelée « haute dose/refuge » (HDR). Cette stratégie repose sur le maintien, à proximité des cultures transgéniques, de cultures « refuges » – exemptes de toxines Bt – constituant des réservoirs d’individus sensibles. Son efficacité est notamment conditionnée par un brassage génétique intense entre ces individus sensibles et les individus résistants sélectionnés dans les parcelles de plantes Bt. Pour plusieurs ravageurs cibles de ces toxines, sa mise en oeuvre a pourtant précédé l’examen détaillé des traits d’histoires de vie pouvant influencer l’intensité de ce brassage. Des études ont, depuis, partiellement comblé ces manques : nous présentons une synthèse de résultats récents sur la pyrale du maïs, une des cibles principales des maïs Bt. Bien que ce papillon ravageur soit hautement polyphage, les populations se nourrissant d’autres plantes hôtes – sauvages ou cultivées – sont trop minoritaires pour limiter efficacement le développement de résistances. Par ailleurs, une partie des pyrales semble se reproduire à proximité immédiate de leur lieu d’émergence, de sorte que des refuges situés à plusieurs centaines de mètres des maïs Bt – la distance maximale autorisée étant actuellement de 800 mètres – ne garantissent pas le brassage génétique entre individus sensibles et résistants. Dans le cas de rotations culturales, ce brassage pourrait néanmoins être accru par une gestion différente des bordures de champs Bt et conventionnels. Bien qu’aucune résistance ne se soit déclarée 10 ans après la mise en culture des premiers maïs Bt, ces données indiquent que la stratégie HDR telle qu’elle est actuellement appliquée n’est pas forcément optimale et, plus généralement, qu’il est illusoire d’espérer définir une stratégie universellement adaptée