Search

New agricultural pest species attacking introduced crops may evolve from pre-existing local herbivores by ecological speciation, thereby becoming a species by becoming a pest. We compare the evolutionary pathways by which two maize pests (the Asian and the European corn borers, ACB and ECB) in the genus Ostrinia (Lepidoptera, Crambidae) probably diverged from an ancestral species close to the current Adzuki bean borer (ABB). We typed larval Ostrinia populations collected on maize and dicotyledons across China and eastern Siberia, at microsatellite and mitochondrial loci. We found only two clusters: one on maize (as expected) and a single one on dicotyledons despite differences in male mid-tibia morphology, suggesting that all individuals from dicotyledons belonged to the ABB. We found evidence for migrants and hybrids on both host plant types. Hybrids suggest that field reproductive isolation is incomplete between ACB and ABB. Interestingly, a few individuals with an 'ABB-like' microsatellite profile collected on dicotyledons had 'ACB' mtDNA rather than 'ABB-like' mtDNA, whereas the reverse was never found on maize. This suggests asymmetrical gene flow directed from the ACB towards the ABB. Hybrids and backcrosses in all directions were obtained in no-choice tests. In laboratory conditions, they survived as well as parental strain individuals. In Xinjiang, we found ACB and ECB in sympatry, but no hybrids. Altogether, our results suggest that reproductive isolation between ACB and ABB is incomplete and mostly prezygotic. This points to ecological speciation as a possible evolutionary scenario, as previously found for ECB and ABB in Europe.

Defining the taxonomic identity of organisms is a prerequisite for their study, and in the case of economically important species, misidentification may lead to the application of inappropriate prevention and control strategies. Flat mites of the Brevipalpus genus include several crop pests and the systematics of these mites represents a challenge for acarologists. Many of the most economically important Brevipalpus species have repeatedly been inaccurately identified. Such problematic classification has been attributed to the likely occurrence of cryptic species in the genus. In this study, we used an integrative approach that combined molecular analyses, including sequence-based species delimitation, with detailed morphological identification using traits that have recently showed to be taxonomically informative. Sequences of mitochondrial cytochrome c oxidase subunit I (COI) were obtained from individuals collected from host plants belonging to 14 genera and 13 families across 29 locations in the Americas (Brazil, Chile, USA). The phylogenetic analyses included previously published Brevipalpus sequences from GenBank, and the final data set was classified into 44 haplotypes. Six putative species were recognised by COI-based species delimitation analysis, and morphological evidence supported each of these species. The integrative approach revealed the occurrence of cryptic species in the Brevipalpus genus and contributed to the clarification of previously noted incongruences. The results presented here allow for the evaluation of taxonomic characteristics in a phylogenetic context and indicate new characters for the differentiation of Brevipalpus species. In addition, Brevipalpus incognitus n. sp. Ferragut & Navia, a cryptic species detected in this study, is described based on morphological and molecular traits. Implications of the advances in Brevipalpus systematics presented herein with respect to pest management are briefly discussed., We sincerely thank Dalva L. de Queiroz Santana, Embrapa Florestas, Colombo, Parana; Aloyseia Noronha, Eduardo Chumbinho de Andrade, Juliana Freitas-Astua and Francisco F. L. Barbosa, Embrapa Mandioca e Fruticultura, Cruz das Almas, Bahia; Alberto Luiz Marsaro Jr, Embrapa Roraima, Boa Vista, Roraima; Ricardo Adaime da Silva, Embrapa Amapa, Macapa, Amapa; Patricia Maria Drumond, Embrapa Acre, Rio Branco, Acre; Manoel Guedes C. Gondim Jr and Aleuny C. Reis, Universidade Federal Rural de Pernambuco, Recife, Pernambuco; Jose. C. M. Poderoso, Universidade Federal de Sergipe, Sao Cristovao, Sergipe, all from Brazil; and Jose Carlos V. Rodrigues, University of Puerto Rico, San Juan, Puerto Rico, for their help with sampling; Tatiane G. C. M. Galasso, Brazil, for help with extensive laboratory work. We also thank Maries Pages and Fabien Condamine, INRA, UMR CBGP, France, for their help concerning the Pons analysis. This study was funded by Brazil - National Council for Scientific and Technological Development (CNPq) (call CNPq/MAPA/SDA No 064/2008, grant 578353/2008-3), Embrapa Macroprograma 3 and Fundacao de Apoio a Pesquisa do Distrito Federal (FAP-DF). Authors DN and RSM are also grateful to CNPq for the research and pos-doc fellowships, respectively.

Root-knot nematodes are globally the most aggressive and damaging plant-parasitic nematodes. Chemical nematicides have so far constituted the most efficient control measures against these agricultural pests. Because of their toxicity for the environment and danger for human health, these nematicides have now been banned from use. Consequently, new and more specific control means, safe for the environment and human health, are urgently needed to avoid worldwide proliferation of these devastating plant-parasites. Mining the genomes of root-knot nematodes through an evolutionary and comparative genomics approach, we identified and analyzed 15,952 nematode genes conserved in genomes of plant-damaging species but absent from non target genomes of chordates, plants, annelids, insect pollinators and mollusks. Functional annotation of the corresponding proteins revealed a relative abundance of putative transcription factors in this parasite-specific set compared to whole proteomes of root-knot nematodes. This may point to important and specific regulators of genes involved in parasitism. Because these nematodes are known to secrete effector proteins in planta, essential for parasitism, we searched and identified 993 such effector-like proteins absent from non-target species. Aiming at identifying novel targets for the development of future control methods, we biologically tested the effect of inactivation of the corresponding genes through RNA interference. A total of 15 novel effector-like proteins and one putative transcription factor compatible with the design of siRNAs were present as non-redundant genes and had transcriptional support in the model root-knot nematode Meloidogyne incognita. Infestation assays with siRNA-treated M. incognita on tomato plants showed significant and reproducible reduction of the infestation for 12 of the 16 tested genes compared to control nematodes. These 12 novel genes, showing efficient reduction of parasitism when silenced, constitute promising targets for the development of more specific and safer control means., Author Summary Plant-parasitic nematodes are annually responsible for more than $100 billion crop yield loss worldwide and those considered as causing most of the damages are root-knot nematodes. These nematodes used to be controlled by chemicals that are now banned from use because of their poor specificity and high toxicity for the environment and human health. In the absence of sustainable alternative solutions, new control means, more specifically targeted against these nematodes and safe for the environment are needed. We searched in root-knot nematode genomes, genes conserved in various plant-damaging species while otherwise absent from the genomes of non target species such as those of chordates, plants, annelids, insect pollinators and mollusks. These genes are probably important for plant parasitism and their absence from non-target species make them interesting candidates for the development of more specific and safer control means. Further bioinformatics pruning of this set of genes yielded 16 novel candidates that could be biologically tested. Using RNA interference, we knocked down each of these 16 genes in a root-knot nematode and tested the effect on plant parasitism efficiency. Out of the 16 tested genes, 12 showed a significant and reproducible diminution of infestation when silenced and are thus particularly promising.

National audience; Root-knot nematodes, Meloidogyne spp., are extremely polyphagous plant parasites worldwide. Since the use of most chemical nematicides is being prohibited, genetic resistance is an efficient alternative way ta protect crops against these pests. However, resistance genes (R-genes) are limited and nematode populations are able ta overcome them with time. Good management of these valuable resources is thus a key point of R-gene durability. ln pepper, Me3 is a dominant major resistance gene, currently used in breeding programs, that control M. arenario, M. incognito and M. javanica, the three main root-knot nematodes species. ln this study, it was introgressed in either a susceptible or a partially resistant genetic background in either homozygous or heterozygous allelic status. Confronting these genotypes with a high inoculation pressure of an avirulent M. incognito isolate or a Me3 virulent laboratory-selected population (obtained by successive re-inoculation on a Me3 R-pepper line) demonstrated i) that the genetic background plays an important raie, Me3 being overcome more easily in a susceptible genetic background than in a partially resistant one, ii) that the allelic status has no effect. These results are in good agreement with concepts recently developed from the analysis of very different plant-pathogen interactions: pepper-virus (Palloix et al., 2009) or rapeseed-Leptosphaeria (Brun et al., 2012). Experiments are now underway ta detect and localise genes or loci providing partial resistance (QTLs = Quantitative Trait Loci) ta root-knot nematodes explaining the differences observed between susceptible and partially resistant genetic backgrounds, and ta determine the effectiveness of their « protective » raie on the major R-genes. Ali these results are of main importance for the creation of new varieties by breeders who have to take into account the plant material used and the resistance gene they want ta introgress.

Expanding genomic data on plant pathogens open new perspectives for the development of specific and environment friendly pest management strategies based on the inhibition of parasitism genes that are essential for the success of infection. Identifying such genes relies on accurate reverse genetics tools and the screening of pathogen knock-down phenotypes. Root-knot nematodes are major cosmopolitan crop pests that feed on a wide range of host plants. Small interfering RNAs (siRNAs) would provide a powerful tool for reverse genetics of nematode parasitism genes provided that they could (1) target genes expressed in inner tissues of infective nematodes and (2) target genes expressed during parasitism. In this study, we show that siRNAs can access inner tissues of the infective juveniles during soaking and accumulate in the esophagus, amphidial pouches and related neurons of the nematode. We provide evidence that siRNAs can trigger knock-down of the parasitism gene Mi-CRT, a calreticulin gene expressed in the esophageal glands of Meloidogyne incognita. Mi-CRT knock-down in infective juveniles affected nematode virulence. However, Mi-CRT knock-down was not persistent after plant infection, indicating that siRNA-mediated RNAi is best suited for functional analysis of genes involved in pre-parasitic stages or in the early steps of infection.

L'utilisation de variétés résistantes constitue un idéal à atteindre en termes d'agriculture durable, en particulier vis-à-vis de Globodera pallida. Ce nématode, strictement inféodé aux solanacées et plus particulièrement à la pomme de terre, provoque des dégâts tant qualitatifs que quantitatifs. Outre son importance économique, G. pallida fait l'objet d'une lutte obligatoire en Europe et dans le monde de par son statut de ravageur de quarantaine. La mise au point de variétés résistantes passe par la recherche du compromis idéal entre efficacité vis-à-vis d'une gamme la plus étendue de populations de G. pallida, durabilité en proposant des variétés dont les résistances ne sont pas contournées rapidement et productivité en assurant de hauts niveaux de rendement en présence du parasite. Pour le moment, une seule variété de consommation résistante à ce nématode est inscrite au catalogue français (Îledher).Cette résistance, provenant de Solanum vernei, s'avère peu durable : cinq générations permettent de sélectionner des individus virulents et d'observer un début de contournement. Nos objectifs sont donc d'identifier la ou les sources susceptibles de fournir des génotypes pouvant prendre le relais de la variété Îledher et présentant un bon compromis entre caractéristiques agronomiques, efficacité et durabilité des résistances., Resistant varieties represent a cost effective and environmentally friendly means to control many pests. They are therefore used extensively as a crop protection strategy. Developing such resistant varieties to control potato cyst nematode Globodera pallida is of paramount interest, especially because of its quarantine status and the obligate management of infested fields. A good resistant variety is the result of the best trade-off between efficiency (against the widest range of the nematode populations), durability (as the variety must provide an efficient protection during repetitive cropping periods) and yield performance (in particular in the presence of nematodes). Presently, only one G. pallida resistant variety, Îledher, is registered in France. Its resistance comes from the related wild species Solanum vernei and the evaluation of its durability under laboratory conditions showed that only five nematode generations were sufficient to select virulent individuals. Our main goals are thus to identify among different related wild species of Solanum (Solanum vernei, S. sparsipilum and S. spegazzinii), new genotypes that can be used as resistant parents for future varieties that will present the best trade-off between efficiency, durabilty and agronomical characteristics and also be able to control the virulentpopulations selected on the variety Îledher, if ever they appeared in the fields.

Afin de pouvoir développer à grande échelle une lutte biologique par Trichogramma chilonis contre le foreur de la canne à sucre, il est nécessaire d’en diminuer les coûts. Savoir stocker les auxiliaires avant leur utilisation sur le terrain représente un avantage indispensable, tant au niveau de la biofabrique que des professionnels sur le terrain. A cet effet, un nouveau programme de recherche, financée par le Ministère Français de l’Agriculture et de la Pêche, est en cours. L’objectif est de déterminer les conditions optimales (T°, HR, photopériode, stade de développement) pour mettre en place un arrêt de développement (quiescence ou diapause). Les premiers résultats obtenus montrent déjà la possibilité de stocker au froid pendant 2 mois, sous forme de quiescence, les Trichogramma produits.

L’importance de la prédation des oeufs du foreur de la canne à sucre, Chilo sacchariphagus, à la Réunion est démontrée et joue un rôle essentiel dans le contrôle naturel de ce ravageur. Elle est principalement exercée par les fourmis de l’espèce Pheidole megacephala. La stratégie de lutte biologique que nous avons mise au point depuis quelques années prend en compte cette action prédatrice qui est particulièrement bénéfique sur des champs de canne âgés de 6 à 12 mois. Toutefois, nos résultats montrent que la prédation des fourmis peut aussi avoir un effet néfaste sur l’auxiliaire utilisé, Trichogramma chilonis, au cours des lâchers. En effet, de par leur comportement très actif et leur petite taille, elles arrivent à pénétrer dans les différents conditionnements testés et à attaquer les oeufs hôtes et les parasitoïdes en cours de développement. Pour limiter cet impact négatif, il est nécessaire d’optimiser le conditionnement, le temps que les trichogrammes émergent et aillent parasiter les oeufs du ravageur.

National audience; La recherche et le développement de nouvelles méthodes de lutte biologique nécessitent un investissement important sur l’optimisation de l’élevage d’insectes (auxiliaires, hôtes ou prédateurs). Cet article décrit les procédures d’élevage d’un parasitoïde, Psyttalia lounsburyi, et de son hôte de substitution Ceratitis capitata. Cet article présente également quatre expérimentations complémentaires visant à mieux documenter la biologie de P. lounsburyi, auxiliaire potentiel de lutte biologique contre la mouche de l’olive, Bactrocera oleae, qui reste le principal ravageur de l’olivier. L’âge de l’hôte, la forme du support de ponte et la présence de mâles adultes sur la production de parasitoïdes sont plus particulièrement étudiés. L’apport de ces informations pour l’optimisation de la production est discuté

La tordeuse sud-africaine de l’oillet Epichoristodes acerbella est un ravageur difficile à combattre par insecticides car son stade sensible est très court et ses générations se chevauchent.[br/] Aussi des essais de lutte biologique sont-ils menés depuis 1998 par une équipe Chambre d’Agriculture, SRPV, INRA, dans le cadre d’un programme ASTREDHOR. Dans ce cadre, des trichogrammes ont été testés comme auxiliaires. Une souche de Trichogramma dendrolimi (souche V) a donné les meilleurs résultats, insuffisants cependant. Parallèlement, une prospection réalisée en 2000 a permis de récolter des auxiliaires indigènes, notamment les trichogrammes T. voegelei et T. cacoeciae.[br/] Dans un essai en serre en 2001, T. voegelei (souche O) et T. dendrolimi (souche V) ont donné les meilleurs résultats en terme de taux moyen de parasitisme, de proportion d’ooplaques parasitées et de capacité de dispersion (différences significatives avec les autres souches) ; T. voegelei avait les meilleurs résultats moyens, mais sans différence significative avec T. dendrolimi .[br/] Des essais vont continuer avec ces deux souches afin d’améliorer l’efficacité des lâchers (effectifs globaux et nombre de points de lâchers, heures des lâchers, diminution de l’aspersion)., The South African carnation tortrix, Epichoristodes acerbella , is a pest which is extremely difficult to control by the use of insecticides since its sensitive stage is extremely short and there is a constant overlap of generations.[br/] In this respect, trials have been carried out since 1998 by a team made up of representatives of the Chamber of Agriculture, the Regional plant protection committee (SRPV) and the national agronomic research institute (INRA), within the framework of an ASTREDHOR programme. In this programme, the possibility of using trichograms as beneficials was put to the test. A strain of Trichogramma dendrolimi (strain V) produced the best results, but these are nevertheless insufficient.[br/] Parallel to these trials, research carried out in 2000 made it possible to collect indigenous beneficials, most notably T. voegelei and T. cacoeciae. In a greenhouse test carried out in 2001, T. voegelei (strain O) and T. dendrolimi (strain V) produced better results in terms of average parasitism levels, proportions of parasite affected eggs and dispersion capability (for which there were significant differences compared to the other strains); T. voegelei produced better average results, but there was no significant difference from T. dendrolimi.[br/] Tests will continue with these two strains in order to improve the efficacy of releases (overall numbers and number of release points, time of release, reduced sprinkling).

National audience; La lutte chimique contre les insectes ravageurs des cultures est souvent mal conçue et mal conduite. Elle a un impact négatif trop important sur l'homme et son environnement. Cet impact peut être aggravé par l'étroitesse des systèmes insulaires tropicaux. La lutte biologique, fondée sur l'utilisation de ressources naturelles par l'homme sans manipulation préalable, a été longtemps sous-estimée dans le cadre de la protection phytosanitaire. Elle repose sur une bonne connaissance des relations parasitaires existantes et nécessite un développement des recherches de base en écologie des populations constituant les agrosystèmes pour en comprendre le fonctionnement. La gestion des régulations naturelles à notre profit passe par leur connaissance approfondie.