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Data are available on CIRAD Dataverse https://doi.org/10.18167/DVN1/NYZ2NR (https://dataverse.cirad.fr).; International audience; When several polyphagous herbivore species share a parasitoid, the tri-trophic interaction networks can be difficult to predict. In addition to direct effects, the parasitoid may influence the herbivore community by mediating indirect interactions among hosts. The plant species can also modulate the parasitoid preference for a specific host. One of the indirect effects is apparent competition, a negative interaction between individuals as a result of the action of shared natural enemies. Here, we focus on the interactions between the parasitoid Fopius arisanus (Braconidae) and two generalist fruit fly pests: Bactrocera dorsalis and Bactrocera zonata (Tephritidae). This parasitoid was introduced into La Reunion in 2003 to control populations of B. zonata and can also interact with B. dorsalis since its invasion in 2017. Our main objective is to characterize the tri-trophic interactions between F. arisanus, fruit fly and host plant species. We developed a long-term field database of fruit collected before and after the parasitoid introduction and after the B. dorsalis invasion in order to compare parasitism rate and fruit fly infestation for the different periods. In laboratory assays, we investigated how the combination of fruit fly species and fruit can influence the preference of F. arisanus. In the field, before the invasion of B. dorsalis, the parasitism rate of F. arisanus was low and had a little impact on the fruit fly infestation rate. After the B. dorsalis invasion, we observed an increase in parasitism rate from 5% to 17%. A bioassay showed that females of F. arisanus could discriminate between eggs of different fruit fly and host plant species. The host plant species preference changed in relation to the fruit fly species inoculated. Field observations and laboratory experiments suggest the possible existence of apparent competition between B. dorsalis and B. zonata via F. arisanus.

International audience; Plantain (Musa paradisiaca AAB) is one of the most important staple crops in the tropics, particularly in theCaribbean. Pests are the main constraint to plantain production and yield increases may be possible by improvingpest management. However, there is a lack of data on these cropping systems and a need to identify new elementsof improved production systems that can control pests in line with the principles of agroecologicaltransition. In this study, we test the hypothesis that crops grown in good quality soils are less susceptible to pests.To this end, an agroecological diagnosis of the biological, physical, morphological and chemical soil conditionsand the occurrence of pests, in particular plant-parasitic nematodes, was carried out on 21 plantain plots withcontrasting management in Guadeloupe (French West Indies). After classifying these plots according to theirmanagement practices, from conventional to agroecological, we searched for relationships between croppingsystems, soil quality and pests using a series of synthetic quality indices. Four different cropping systems wereidentified and compared: conventional intensive, intermediate, low-input and agroecological, according to thetype and amount of agrochemicals used. Our data showed that the Chemical Index was significantly improved inthe agroecological systems due to increases in pH, CEC, base saturation and total C and N content. TheMorphological Index increased regularly from intensive to agroecological systems and was significantly higher inagroecological systems with higher proportions of biogenic aggregates. Soil macroinvertebrate communitieswere significantly influenced by production systems, with the highest values of the Macrofauna Index in lowinput and agroecological production systems. We also showed that plant parasitic nematodes were betterregulated in agroecological production systems. Furthermore, the agroecological system achieved similar levelsof crop production to conventional systems, without the use of pesticides. In addition, these agroecologicalcropping systems extend the duration of plantain plots, which is an indicator of the good health of these systems.

In Western Burkina Faso, fruit flies (Diptera: Tephritidae) cause economic impacts. Damage on a mango can reach 100% in late varieties, and on shea fruits, the average attack rate is 66.5%. Parasitoids offer natural biocontrol services, but the potential for this in Burkina Faso remains unknown. We performed a survey (2017–2019) in three plant formations (natural fallows n = 6; agroforestry parks n = 6 and mango orchards n = 6) to determine the levels of parasitism of tephritid fruit fly pests. For this purpose, fruits from cultivated and wild fruit fly host plant species were sampled in these plant formations and incubated for insects' emergence. In total, 1822 adults belonging to 7 parasitoid species were found. Fopius caudatus (Szépligeti) and Psyttalia concolor (Szépligeti) with 51.47% and 30.60% of the total of parasitoid adults emerged, respectively, were the most predominant. Parasitism rate varied according to host fruit species. Pupae recorded from Sarcocephalus latifolius and Vitellaria paradoxa were most parasitized (27.22% ± 3.96%) and (17.08% ± 2.37%), respectively, while those obtained from mangoes were the less parasitized (3.73% ± 0.91%). Mass rearing of F. caudatus and P. concolor, as well as habitat management, will contribute to the promotion of both, augmentation and conservation biological control.

The South American tomato pinworm, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), has invaded most Afro-Eurasian countries and is threatening worldwide tomato production. Various strategies have been developed and implemented to manage this pest. Here, we present a timely review on the up-to-date development and practical implementation of integrated pest management (IPM) programs for tomato crops across different world regions infested by T. absoluta. While insecticide resistance is a growing concern, biological control via releasing or conserving arthropod natural enemies and sex pheromone-based biotechnical control are the most successful management practices. Agronomic control-related research is an emerging area where the soil fertilization and/or irrigation, as well as breeding of resistant cultivars, has the potential to enhance IPM effectiveness. Grower survey responses in the native areas (i.e., South America), early-invaded areas (i.e., first report between 2006 and 2012) and newly invaded areas (i.e., first report after 2012) showed that the control programs evolved along with the areas and time since invasion. Growers in the early-invaded areas shifted more rapidly from chemical control to biological control compared to those from the native area. In all concerned regions, the pest control failure risk following chemical insecticide applications and the high cost associated with either biological or biotechnical control methods have been the greatest concerns for growers. The information gathered from the native and/or early-invaded areas may help achieve a more effective management in newly invaded areas. Lastly, researchers are expected to break the bottlenecks of some key issues that would enable lowering application cost of novel biorational alternative management options.

International audience; Gall midges (Diptera: Cecidomyiidae) comprise a diverse family of small nematoceran flies. While most species are phytophagous, the family also includes predatory species, and endoparasitoids. Endoparasitic species have been reared from aphids and psyllids. We discovered parasitoid-infected weaver ant, Oecophylla longinoda (Latreille) (Hymenoptera: Formicidae) in nests on mango trees in coastal Kenya. Examination of 5 colonies revealed the presence of parasitoids in all of them, with parasitism rates ranging from 2 to 21%. Morphological examination of larval parasitoids indicated that they were gall midges, and molecular data were consistent with the identification. Attempts to rear adults were unsuccessful. This study presents to the best of our knowledge the first report of Cecidomyiidae parasitising Hymenoptera, as well as the first report of a parasitoid of weaver ants. This species should be investigated further because its damage may limit the ability of weaver ants to control pests of cultivated fruits and other insects.

Semiochemicals such as herbivore-induced plant volatiles (HIPVs) and host chemicals serve as communication signals for parasitoids searching for oviposition sites. The braconid koinobiont endoparasitoid Dolichogenidea gelechiidivoris (Hymenoptera: Braconidae) efficiently parasitises larvae of Tuta absoluta (Lepidoptera: Gelechiidae), a major pest of tomato (Solanum lycopersicum). However, the attractive compounds used by the parasitoid to locate T. absoluta on host plants are not known. We therefore performed behavioural assays and chemical analyses to investigate the chemical basis of interactions between the parasitoid, the tomato plant and T. absoluta. Y-tube olfactometer bioassays revealed that D. gelechiidivoris was attracted to T. absoluta larvae-infested tomato plant volatiles and preferred volatiles of plants with a high infestation level than those with a low infestation level. The parasitoid was also attracted to volatiles of larval frass and to the sex pheromone of T. absoluta. Coupled gas chromatography–mass spectrometric analyses were performed on plant and frass volatiles. We found both qualitative and quantitative differences in volatile emission between healthy and T. absoluta larvae-infested tomato plants, where volatile emission rate increased with increasing infestation level. The most characteristic volatile compounds which distinguished T. absoluta larvae-infested plants from healthy plants were α-pinene, sabinene, β-myrcene, 2-carene, α-phellandrene, 3-carene, α-terpinene, β-phellandrene, (Z)-β-ocimene, (E)-β-ocimene, allo-ocimene, (E)-β-caryophyllene and methyl salicylate. With the exception of caryophyllene oxide, all larval frass volatile compounds were also found in tomato plant headspace volatiles. Olfactometer bioassays using synthetic compounds revealed that D. gelechiidivoris was attracted to α-pinene, β-myrcene, α-phellandrene, α-terpinene, β-ocimene, methyl salicylate and (E)-β-caryophyllene, and the 7-component blend of these attractants elicited the greatest attraction in the parasitoid. These findings open new avenues for exploiting these attractants as kairomone-based lures to recruit and retain the parasitoid in tomato fields for the biological control of T. absoluta.

Whiteflies are one of the major pests of tomato under greenhouses, and their control partly relies on biocontrol strategies. Among those biocontrol agents, parasitoids or predators are widely used. However, the introduction of a biocontrol agent in a new area is not trivial. For that reason, we investigated the use of a tropical native mirid, Nesidiocoris volucer (Hemiptera: Miridae), for the biological control of whiteflies among other insect pests on tomato crops under greenhouses in the subtropical island of La Réunion, France. Nesidiocoris volucer life history traits and plant injury were examined. Nymphs developed and survived between 15 and 30°C and required on average 49.41 days at 15°C and on average 10.50 days at 30°C to develop (nymph survival >94%). At 25°C, each female produced on average 65 eggs. Nesidiocoris volucer was able to feed on several prey species, but performed better on whiteflies than on spider mites or thrips. No N. volucer feeding injury was observed on tomato. Nesidiocoris volucer has also been found in tropical countries of Africa, and we believe that the data presented on this natural enemy could be of great importance for the biocontrol of whiteflies in tropical areas.

The sterile insect technique (SIT) is a method of biological control of pests and disease vector insects. It includes mass-rearing and release of sterile males of the target species so that wild females mated with sterile males would not produce offspring. An innovative version of this technique, called boosted SIT, relies on the use of sterile males as vectors of biocides to trigger an epizootic in the wild fruit fly population. We built an agent-based model to assess the feasibility of this technique and main modalities of field implementation for the control of the Oriental fruit fly, Bactrocera dorsalis, using the entomopathogenic fungi, Metarizhium anisopliae, as a biocide. The model, called BOOSTIT (BactrOcera dOrsaliS boosTed sIT), simulates the spatio-temporal population dynamics of fruit flies in three different realistic landscape contexts. The releases of infected and uninfected sterile males were simulated and allowed the transmission of the pathogen within the wild fly population as a result of interactions between individuals. A main output was the measurement of losses in mango production. Validation of the model was done by comparing the simulated population dynamics with data from field monitoring (pheromone traps) in three landscapes of the Niayes area in Senegal. The population dynamics of wild flies were then simulated in an intensive cropping and mono-mango cultivar landscape under three scenarios: (1) without the release of sterile males, (2) with the release of non-contaminated sterile males (SIT) and (3) with the release of sterile contaminated males (boosted SIT). The results showed that SIT and boosted SIT strongly reduced the density of wild flies and the amount of infested fruits. Although parameters of the pathogen transfer between individuals need to be studied more deeply, results encourage the implementation of field trials to validate the efficacy of boosted SIT to control fruit flies.

Introduire des parasitoïdes sur un territoire pour contrôler un ravageur est une opération de longue haleine. Voici l'analyse d'un premier échec et les perspectives de la lutte biologique contre Rastrococcus invadens en Guyane française. Contexte : En septembre 2014, l'espèce invasive, Rastrococcus invadens Williams (Hemiptera : Pseudococcidae) a été détectée à Cayenne (Guyane), puis rapidement identifiée par le LSV-Anses. C'est le premier signalement de la cochenille sur le continent sud-américain. À la demande du ministère de l'Agriculture, une mission a été réalisée par le Centre de coopération internationale en recherche agronomique pour le développement (CIRAD) fin 2016 afin de définir la gamme des plantes-hôtes de R. invadens, l'importance des dégâts au niveau des plantes cultivées et d'actualiser la distribution du bioagresseur dans le département. Etude : En 2019, un programme de lutte biologique a débuté par la création, à Kourou, d'un laboratoire d'entomologie permettant le confinement de macro-organismes auxiliaires non indigènes. En janvier 2021, des micro-hyménoptères parasitoïdes, Gyranusoidea tebygi Noyes et Anagyrus mangicola Noyes (Hymenoptera Encyrtidae), ont été importés à partir de la station d'International Institute of Tropical Agriculture (IITA), située au Bénin, et installés dans le laboratoire de Kourou afin de les multiplier, de confirmer leur spécificité vis à-vis de R. invadens puis de les lâcher. Résultats : Les élevages de parasitoïdes auxiliaires n'ont pas pu se développer durablement et les deux souches d'Encyrtidae se sont éteintes en juin 2021 dans le laboratoire de Kourou. Plusieurs raisons peuvent en être la cause et sont discutées dans cet article. D'autres voies pour soutenir la lutte biologique contre ce ravageur d'importance seront également étudiées afin d'offrir des perspectives aux producteurs, notamment aux agrumiculteurs particulièrement touchés, et depuis peu, sous une autre menace phytosanitaire, le Huanglongbing.

L’utilisation des pesticides chimiques de synthèse dans la protection des cultures a aujourd’hui clairement montré ses limites : risques sanitaires, effets négatifs sur l’environnement, déséquilibres écologiques, pertes d’efficacité et coûts élevés. C’est pourquoi la forte réduction de ces pesticides est maintenant un objectif généralement admis par la plupart des acteurs professionnels et politiques. En France, le biocontrôle est un concept de protection des cultures apparu lors de la dernière décennie et présenté comme une solution permettant de réduire l’utilisation de pesticides. La présente synthèse vise à dresser un état des lieux de ce que recouvre le terme de « biocontrôle » en France. Derrière une définition officielle, la revue des définitions du biocontrôle en France montre une instabilité terminologique significative. La diversité des acceptions du terme de « biocontrôle » est à l’origine d’interprétations variables selon les acteurs. Par ailleurs, l’analyse de l’utilisation du terme « biocontrôle » en France au cours de la dernière décennie montre l’intérêt grandissant du biocontrôle auprès du grand public, des professionnels du monde agricole et agropharmaceutique, des politiques et de la communauté scientifique. L’augmentation de l’usage de ce terme a été observée parallèlement à la diminution de l’usage du terme « lutte biologique », un concept reconnu et stable depuis plus d’un siècle. Enfin, cette diversité des définitions du biocontrôle et cette augmentation de l’utilisation du terme « biocontrôle » induisent des problématiques dans le domaine de la protection des cultures qui sont évoquées dans cette synthèse.

Callosobruchus maculatus Fab. (Coleoptera: Chrysomelidae) is a major pest of stored cowpea in West Africa, responsible for significant weight losses and grain deterioration during storage. Biological control of this pest using its native larval (Dinarmus basalis) and oophagous (Uscana lariophaga) parasitoids is currently investigated. The present study aims to assess into experimental storage systems the effects of five options of releasing U. lariophaga and D. basalis, alone or in combination, on the populations of C. maculatus in comparison with a control without any parasitoid. The combined releases of the two parasitoid species prevented the increase in C. maculatus numbers better than the release of a single parasitoid species. Each parasitoid species behaved differently when alone versus in combination. Thus, D. basalis had a higher development and rates of parasitism when it was alone, whereas the opposite was observed in U. lariophaga, whose parasitism activity seemed to be stimulated by the presence of D. basalis. After 150 days of storage, the cowpea seed losses were estimated to be significantly lower (9–13%) in all parasitoid combination treatments instead of 31% and 62% in single parasitoid treatments and the control, respectively. Our results suggest that combined releases of both parasitoids can additively control the pest and maintain cowpea quality over 5 months of storage. Further studies should precise the optimal densities of each species to be released without additional introductions throughout the storage period. Interactions between D. basalis and U. lariophaga are still poorly known and will require in-depth scientific investigations.

Contexte : Malgré des be- soins toujours plus pressants de trouver des alternatives aux produits phytopharmaceutiques, force est de constater que le secteur des macro-organismes de biocontrôle peine à se généraliser dans la pratique et, avant tout, à s'imposer dans l'esprit des parties intéressées : les utilisateurs finaux (les agriculteurs), les conseillers techniques, mais également les politiques et les financeurs. Stratégies de lutte : La régulation des bioagresseurs peut se réaliser en favorisant les individus déjà présents dans ou aux alentours des parcelles cultivées : c'est ce que l'on appelle la lutte biologique par conservation. Elle peut également se faire en introduisant certains auxiliaires délibérément dans les parcelles cultivées (acclimatation, augmentation, lutte autocide). Cet article présente les stratégies de biocontrôle à l'aide de macro-organismes (essentiellement des insectes, acariens ou nématodes entomopathogènes), qu'elles soient pratiquées depuis longtemps en France, plus récemment implantées, voire encore prospectives.

International audience; The African mirid bug (Sahlbergella singularis) is the most economically important insect pest in cocoa farms. Pesticide management, although controversial due to the adverse effects of these substances on the environment and on human health, remains the main option used for controlling this pest. In the recent decades, the development of alternative approaches to synthetic pesticides is a requirement. Therefore, we used neem oil (NO) and ethanolic extracts (EE) from leaves at different concentrations to evaluate, in vitro, their insecticidal potentials against mirids. Mirid mortality increased significantly with increase in concentrations, values ranged from 32.5 to 92.5% for EE and 52.5 to 97.5% forNO. Apart from negative controls, Tween 80 and distilled water, that showed significant low mortality rates, both extracts revealed effectiveness comparable to the reference insecticide used in controlling mirids, except for EE by ingestion. Mirids treated by contact showed significantly high mortality rates (72.5 to 97.5 %) compared to those treated by ingestion (32.5 to 70.0 %). The greatest biological effectiveness values were obtained at a concentration of 8 % by contact exposure: 0.88 ml/ml (NO) and 0.73 g/ml (EE) for LC50 and =1 day to both extracts for LT50. Given effectiveness comparable to that of the insecticide, both tested extracts should be considered as effective biopesticides for IPM against mirids, especially S. singularis.

The Bemisia tabaci (Gennadius) whitefly is a major economically damaging pest of many crops such as tomato (Solanum lycopersicum L.). Pesticides are widely used to control B. tabaci while the use of aromatic plants is an alternative control method. The aim of this study was to assess the B.tabaci repellent effect of wild oregano, Plectranthus amboinicus (Lour.) Spreng, a widespread aromatic plant in the West Indies. We tested three origins of wild oregano, including northern, central, and southern Martinique (French West Indies). Our results showed that all essential oils of wild oregano had either masking properties or were true repellents—the mean percentage of whiteflies present in the upper part of the still-air olfactometer was 1.3- to 1.9-fold lower than in the controls. The ethanolic solution of volatile organic compounds of wild oregano from southern Martinique also had a true repellent effect—the mean percentage of whiteflies present in the upper part of the still-air olfactometer was 1.3-fold lower than in the controls. Moreover, in a greenhouse insect-proof cage, there were 1.5 fewer adult whiteflies on tomato intercropped with wild oregano from southern Martinique than on tomato alone after 96 h exposure. Our study generated further insight into the potential of P. amboinicus for B. tabaci biocontrol on tomato crops. Wild oregano extracts were repellent to B. tabaci and could be used as a companion plant to prevent whitefly infestations on tomato crops. However, the B. tabaci behavior depends on the plant origin.

Advances in viral metagenomics have paved the way of virus discovery by making the exploration of viruses in any ecosystem possible. Applied to agroecosystems, such an approach opens new possibilities to explore how viruses circulate between insects and plants, which may help to optimise their management. It could also lead to identifying novel entomopathogenic viral resources potentially suitable for biocontrol strategies. We sampled the larvae of a natural population of alfalfa weevils (Hypera postica), a major herbivorous pest feeding on legumes, and its host plant alfalfa (Medicago sativa). Insect and plant samples were collected from a crop field and an adjacent meadow. We characterised the diversity and abundance of viruses associated with weevils and alfalfa, and described nine putative new virus species, including four associated with alfalfa and five with weevils. In addition, we found that trophic accumulation may result in a higher diversity of plant viruses in phytophagous pests compared to host plants.

BACKGROUND: Biological control plays a key role in reducing crop damage by Tuta absoluta (Meyrick) and Trialeurodes vaporariorum (Westwood), which cause huge yield losses in tomato (Solanum lycopersicum L.). The mirid predator Nesidiocoris tenuis (Reuter) preys heavily on these pests, with satisfying control levels in tomato greenhouses. Although N. tenuis is known to be attracted to volatiles of tomato plants infested by T. absoluta and whitefly, little is known about the specific attractive compounds and the effect of prey density on the predator response. RESULTS: Y-tube olfactometer bioassays revealed that the attraction of N. tenuis to tomato volatiles was positively correlated with the density of T. absoluta infestation, unlike T. vaporariorum infestation. The predator was also attracted to volatiles of T. absoluta larval frass, but not to T. vaporariorum honeydew or T. absoluta sex pheromone. Among the herbivore-induced plant volatiles (HIPVs) that characterised the attractive plants infested with 20 T. absoluta larvae, olfactometer bioassays revealed that N. tenuis is attracted to the monoterpenes α-pinene, α-phellandrene, 3-carene, β-phellandrene and β-ocimene, whereas (E)-β-caryophyllene was found to repel the predator. In dose–response bioassays, the five-component blend of the attractants elicited a relatively low attraction in the predator, and removal of β-phellandrene from the blend enhanced the attraction of the predator to the resulting four-component blend, suggesting synergism among four monoterpenes. CONCLUSION : These findings suggest that a four-component blend of α-pinene, α-phellandrene, 3-carene and β-ocimene could be used as a kairomone-based lure to recruit the predator for the biological control of T. absoluta and T. vaporariorum.

The banana weevil (also known as banana root borer) Cosmopolites sordidus Germar (Coleoptera Curculionidae) is the major pest of banana and plantain. Because banana ranks 2nd in fruit production worldwide, this pest has substantial social and economic importance. The biological control of the C. sordidus remains challenging because of its behaviour and resistance to parasitism and predation. The last review concerning the biological control of C. sordidus was published two decades ago, and relevant knowledge and methods have developed in the interim. The present paper provides an update of that knowledge and summarizes past and current challenges as well as providing perspectives on achieving sustainable control of C. sordidus. We first discuss studies on the classical biological control of C. sordidus, underlining the limits of classical biological control methods such as the importation of predators, parasitoids or pathogens. Next, we consider conservation biological control of C. sordidus, with a focus on ants. We also highlight an 'arthropod bias' that has led to a lack of information on the role of vertebrates in the regulation of C. sordidus.

Tuta absoluta is one of the most damaging pests of tomato crops worldwide. Damage due to larvae may cause up to 100% loss of tomato production. Use of natural enemies to control the pest, notably predatory mirids such as Nesidiocoris tenuis and Macrolophus pygmaeus, is increasingly being promoted. However, considering the potential damage caused to tomatoes by these omnivorous predators in the absence of T. absoluta, an alternative solution could be required to reduce tomato damage and improve the predators’ performance. The use of companion plants can be an innovative solution to cope with these issues. The present study aimed to determine the influence of companion plants and alternative preys on the predators’ performance in controlling T. absoluta and protecting tomato plants. We evaluated the effect of predators (alone or combined) and a companion plant (sesame (Sesamum indicum)) on T. absoluta egg predation and crop damage caused by N. tenuis. The influence of an alternative prey (Ephestia kuehniella eggs) on the spatial distribution of predators was also evaluated by caging them in the prey presence or absence, either on tomato or sesame plants or on both. We found that the presence of sesame did not reduce the efficacy of N. tenuis or M. pygmaeus in consuming T. absoluta eggs; hatched egg proportion decreased when N. tenuis, M. pygmaeus, or both predators were present. More specifically, this proportion was more strongly reduced when both predators were combined. Sesame presence also reduced necrotic rings caused by N. tenuis on tomato plants. Nesidiocoris tenuis preferred sesame over tomato plants (except when food was provided only on the tomato plant) and the upper part of the plants, whereas M. pygmaeus preferred tomato to sesame plants (except when food was provided only on the sesame plant) and had no preference for a plant part. Combination of predators N. tenuis and M. pygmaeus allows for better coverage of cultivated plants in terms of occupation of different plant parts and better regulation of T. absoluta populations. Sesamum indicum is a potential companion plant that can be used to significantly reduce N. tenuis damage to tomatoes.

The moth stem borers Chilo sacchariphagus Bojer (Crambidae) and Tetramoera schistaceana Snellen (Tortricidae) have been found to cause serious damage to sugarcane in Guangxi, China. Although various control strategies are used for the management of stem borers, biological control with Trichogramma parasitoid wasps and application of pheromone traps for monitoring and mass trapping of moth borers have been extensively adopted in area-wide integrated pest management. This paper provides an overview on the management of moth borers based on biological control with Trichogramma and using pheromone traps.

Recent viral zoonotic epidemics have been attributed partially to the negative impact of human activities on ecosystem biodiversity. Agricultural activities, particularly conventional crop protection (CP) practices, are a major threat to global biodiversity, ecosystem health and human health. Here we review interactions between CP practices and viral zoonoses (VZs), the first time this has been done. It should be noted that a) VZs stand at the interface between human, animal and ecosystem health; b) some VZs involve arthropod vectors that are affected by CP practices; and c) some crop pests, or their natural enemies are vertebrate reservoirs/carriers of certain VZs, and their contact with humans or domestic animals is affected by CP practices. Our review encompasses examples highlighting interactions between VZs and CP practices, both efficiency improvement-based (i.e. conventional with agrochemical insecticides and rodenticides), substitution-based (i.e. mainly with physical/mechanical or biopesticidal pest control), and redesign-based (i.e. mainly with conservation biological pest control, including some forms of crop-livestock integration). These CP practices mainly target arthropod and vertebrate pests. They also target, to a lesser extent, weeds and plant pathogens. Conventional and some physical/mechanical control methods and some forms of biopesticidal and crop-livestock integration practices were found to have mixed outcomes in terms of VZ risk management. Conversely, practices based on biological control by habitat conservation of arthropod or vertebrate natural enemies, falling within the Agroecological Crop Protection (ACP) framework, result in VZ prevention at various scales (local to global, and short-term to long-term). ACP addresses major global challenges including climate resilience, biodiversity conservation and animal welfare, and helps integrate plant health within the extended “One Health” concept.

Understanding of driving forces that affect diversity in herbivorous insect communities figures prominently in ecological research, and is necessary for integrated pest management, because some herbivorous insect can become crop pests. Natural enemies and environmental variables are among factors that structure herbivorous insect communities. While natural enemies regulate herbivorous insects, environmental variables affect their diversity and their spatial distribution. The main goal of this thesis was to understand effects of landscape features on diversity of herbivorous thrips communities along elevational gradients in Reunion, and to investigate effects of natural enemy diversity in biological control of pest thrips. In first study, thrips were sampled along replicated elevational gradients, and at each sampling site, landscape features and abiotic variables were estimated within buffers surrounding the site. Study has shown that the greatest diversity of thrips in Reunion is concentrated at lower elevation, although habitats situated in these localities are highly degraded. Thrips diversity was not affected by fragmentation but landscape heterogeneity and habitat amount interacted to affect positively thrips diversity.In second study, we manipulated communities composed of two pest thrips Thrips parvispinus and Frankliniella occidentalis, and two predatory mites Amblyseius swirskii and Proprioseiopis mexicanus. These communities were in cages and were established in greenhouse. Study has shown that both predators are better than one in thrips regulation. That confirms the necessity to maintain biodiversity at the upper trophic level for herbivore control. Moreover, this study revealed that despite intraguild predation, predators would have coexisted because of competition-colonization trade-off., La connaissance des patrons de diversité des communautés d’insectes herbivores occupe une part importante dans la recherche écologique. Elle est nécessaire en vue d’une lutte biologique, sachant que certains insectes herbivores sont capables de devenir des ravageurs de cultures. Les ennemis naturels et les variables environnementales font partie des facteurs structurant les communautés d’insectes herbivores. Alors que les ennemis naturels assurent la régulation des insectes herbivores, les variables environnementales vont plutôt influencer leur diversité et leur distribution spatiale. L’objectif principal de cette thèse était de comprendre les effets des traits de paysage sur la diversité des communautés de thrips herbivores suivant le gradient altitudinal de La Réunion et d’étudier les effets de la diversité des ennemis naturels dans le contrôle biologique des thrips ravageurs. Dans la première étude, les thrips ont été échantillonnés suivant des gradients d'altitude répliqués, et à chaque site d'échantillonnage, les caractéristiques du paysage et les variables abiotiques ont été estimées dans des zones tampons entourant le site. L’étude a révélé que la plus grande diversité des thrips à La Réunion se concentre en basse altitude, bien que les habitats dans ces altitudes soient fortement dégradés. La diversité des thrips a été particulièrement insensible à la fragmentation et, l’hétérogénéité du paysage et la quantité d’habitat ont interagi pour affecter positivement la diversité des thrips. Dans la deuxième étude, nous avons manipulé dans des cages placées sous serre, des communautés composées de deux thrips ravageurs, Thrips parvispinus et Frankliniella occidentalis, et deux espèces d’acariens prédateurs Amblyseius swirskii et Proprioseiopis mexicanus. L’étude a montré que deux prédateurs assurent une meilleure régulation qu’un seul prédateur, confirmant ainsi l’importance de maintenir de la biodiversité au niveau trophique supérieur dans le contrôle biologique des herbivores. Par ailleurs, l’étude a révélé l’existence possible d’un compromis entre la compétition pour la ressource et la dispersion chez les prédateurs, appelé «The, competition-colonization trade-off », permettant ainsi leur coexistence malgré leur interaction dans une prédation intraguilde.

Les mélanges de cultures intermédiaires multiservices (CIMS) de crucifères et de légumineuses permettent une mutualisation des services écosystémiques liés aux cycles de l'azote, du soufre, et à leur potentiel de bio-contrôle sur des bioagresseurs et ravageurs telluriques. Leur association permet d'atteindre un effet piège à nitrate et à sulfate similaire aux CIMS de crucifères pures tout en produisant un meilleur effet engrais vert pour l'azote. Le potentiel de bio-contrôle des CIMS de crucifères a été évalué par leur production de glucosinolates (GSL) qui varie fortement entre les espèces mais peu entre variétés d'une même espèce. Les GSL de type aliphatique contenus dans le radis fourrager semblent les plus à même de réduire l'incidence et la sévérité du Verticillium dahliae sur le tournesol au champ. Aucun effet larvicide ou larvifuge des crucifères n'a pu être mis en évidence sur les larves d'Agriotes sordidus du maïs contrairement au tourteau de moutarde éthiopienne qui augmente significativement la mortalité des larves en conditions contrôlées.