Guide d’identification des Invertébrés de Kerguelen et Crozet

National audienc

Predicting the seasonal flight activity of Myzus persicae , the main aphid vector of Virus Yellows in sugar beet

International audienceBackgroundVirus Yellows (VY), a disease caused by several aphid-borne viruses, is a major threat to the global sugar beet production. Following the ban of neonicotinoid-based seed treatments against aphids in Europe, increased efforts are needed to monitor and forecast aphid population spread during the sugar beet growing season. In particular, predicting aphid flight seasonal activity could allow anticipation of the timing and intensity of crop colonisation and contribute to the proper implementation of management methods. Forecasts should be made early enough to assess risk, but can be updated as the season progresses to refine management. Based on a long-term suction-trap dataset gathered between 1978 to 2014, we built and evaluated a set of models to predict the flight activity features of the main VY vector, Myzus persicae, at any location in the French sugar beet production area (circa 4.105 ha). Flight onset dates, length of flight period and cumulative abundance of flying aphids were predicted using climatic and land-use predictors as well as geographical position.ResultsOur predictions outperformed current models published in the literature. The importance of the predictor variables varied according to the predicted flight feature but winter and early spring temperature always played a major role. Forecasts based on temperature were made more accurate by adding predictors related to aphid winter reservoirs. In addition, updating the model parameters to take advantage of new weather data acquired during the season improved the flight forecast.ConclusionOur models can be used as a tool for the mitigation in sugar beet crops

Prévoir les vols de pucerons virulifères grâce à l'épidemiosurveillance

National audienc

A Link Between Communities of Protective Endosymbionts and Parasitoids of the Pea Aphid Revealed in Unmanipulated Agricultural Systems

International audienceIn the last decade, the influence of microbial symbionts on ecological and physiological traits of their hosts has been increasingly recognized. However, most of these effects have been revealed under laboratory conditions, which oversimplifies the complexity of the factors involved in the dynamics of symbiotic associations in nature. The pea aphid, Acyrthosiphon pisum , forms a complex of plant-adapted biotypes, which strongly differ in the prevalence of their facultative endosymbionts. Some of the facultative endosymbionts of A. pisum have been shown to confer protection against natural enemies, among which Hamiltonella defensa is known to protect its host from parasitoid wasps. Here, we tested under natural conditions whether the endosymbiont communities of different A. pisum biotypes had a protective effect on their hosts and whether endosymbiotic associations and parasitoid communities associated with the pea aphid complex were linked. A space-time monitoring of symbiotic associations, parasitoid pressure and parasitoid communities was carried out in three A. pisum biotypes respectively specialized on Medicago sativa (alfalfa), Pisum sativum (pea), and Trifolium sp. (clover) throughout the whole cropping season. While symbiotic associations, and to a lesser extent, parasitoid communities were stable over time and structured mainly by the A. pisum biotypes, the parasitoid pressure strongly varied during the season and differed among the three biotypes. This suggests a limited influence of parasitoid pressure on the dynamics of facultative endosymbionts at a seasonal scale. However, we found a positive correlation between the α and β diversities of the endosymbiont and parasitoid communities, indicating interactions between these two guilds. Also, we revealed a negative correlation between the prevalence of H. defensa and Fukatsuia symbiotica in co-infection and the intensity of parasitoid pressure in the alfalfa biotype, confirming in field conditions the protective effect of this symbiotic combination

Variations in community assemblages and trophic networks of aphids and parasitoids in protected crops

International audienceGreenhouse crops are thought to be simplified ecosystems because they often consist of mono-cultures that are relatively isolated from their environment. However, insect pests are still able to colonize these protected crops, which threaten their yields. Similarly, natural enemies of pests may be able to colonize greenhouses, providing a form of natural biological pest control. Protected strawberry crops are grown in several types of greenhouses that vary in their degree of openness. Crops often suffer from aphid outbreaks, which can be partly controlled by insect parasitoids immigrating from the surrounding environment. We investigated variations over space and time in both the aphid and parasitoid community diversity and species assemblages associated with protected strawberry crops. We sampled aphids and parasitoids in five regions of France in the spring and summer of two successive years. Despite the relative isolation of these protected crops, we identified a high aphid species richness in them, even at the greenhouse scale. Aphid community composition varied with spatial and temporal factors, but the species assemblages present were mostly determined by local factors. Parasitoid communities were mostly similar among the studied regions, but varied between seasons, with this temporal variation being related to changes in aphid species composition. The study of trophic interactions occurring between aphids and parasitoids allowed the most prevalent and efficient parasitoid species to be identified. The structures of food webs strongly varied in time and space, compromising any prediction of "natural" biological control. We also highlighted ecological factors that can disrupt aphid biological control, such as the occurrence of hyperparasitism or the possibility of apparent mutualism between aphid species. Finally, we showed that the degree of openness of greenhouses influenced both the aphid communities and the hyperparasitism rates in them. These results provide valuable information to improve aphid biological control in protected crops

Variable impacts of prevalent bacterial symbionts on a parasitoid used to control aphid pests of protected crops

International audienceThe ecological role of bacterial symbionts associated with insects is increasingly recognized. Notably, aphids are known to harbour facultative bacterial symbionts that influence their phenotypes like conferring a protection against natural enemies. The most well-known Gamma-Proteobacteria Hamiltonella defensa can provide a defence against hymenopteran parasitoids to their aphid hosts. Aphidiine parasitoids are broadly used as biological control agents in inundative releases against aphids of various greenhouse crops so that defensive symbionts can potentially compromise efficiency of the released parasitoids. Here, we first measured the prevalence and spatiotemporal dynamics of bacterial symbionts infecting eight aphid species colonizing protected strawberry crops in France. Considering the three major aphid pest species of strawberry crops (Acyrthosiphon malvae (Mosley), Macrosiphum euphorbiae (Thomas) and Rhodobium porosum (Sanderson)), we then estimated their possible effects on protection against Aphidius ervi (Haliday), a parasitoid species currently used as a biological control agent. Both symbiotic composition and symbiont prevalences highly differed between aphid species. In the three dominant aphid species, many individuals were single infected or co-infected with H. defensa and Regiella insecticola. Prevalences of these bacterial symbionts highly varied across French regions. Parasitism experiments showed that infection with R. insecticola did not provide any protection against parasitoids while infection with H. defensa would be associated with a strong reduction of parasitism in A. malvae only. These results are valuable to understand the implications of defensive symbionts in the effectiveness of biological control

After spring, after crops: which alternative hosts for the generalist parasitoid Diaeretiella rapae (Hymenoptera: Braconidae)?

International audienceGeneralist aphid parasitoids seem to behave as specialists at the local scale. The temporal pattern of host exploitation by parasitoids is key to understand this result. We investigated the temporal dynamics during twenty-one consecutive months of host exploitation by Diaeretiella rapae (M'Intosh) (Hymenoptera: Braconidae), one of the most generalist aphid parasitoid, in cultivated and uncultivated areas. We applied two complementary approaches: molecular detection of parasitism within living aphids and rearing of aphid mummies collected in Brassicaceae crops and adjacent areas. We built a Maximum Likelihood tree to determine the influence of host plant and aphid species on the genetic structure of D. rapae. We confirmed the existence of a cryptic species developing on Hayhurstia atriplicis (L.) (Hemiptera: Aphididae), but we found no other host-related genetic variation. D. rapae exploited almost exclusively Brevicoryne brassicae (L.) (Hemiptera: Aphididae), a pest of Brassiceae and rarely other hosts. When the crop is absent, D. rapae parasitized B. brassicae on wild Brassicaceae and cover crop instead of alternative aphid host on other plants. These results show the limited role of uncultivated habitats as a reservoir for D. rapae and the interest of wild Brassiceae and cover crops to enhance the control of B. brassicae

Relative importance of long‐term changes in climate and land‐use on the phenology and abundance of legume crop specialist and generalist aphids

International audienceInsect populations are prone to respond to global changes through shifts in phenology, distribution and abundance. However, global changes cover several factors such as climate and land-use, the relative importance of these being largely unknown. Here, we aim at disentangling the effects of climate, land-use, and geographical drivers on aphid abundance and phenology in France, at a regional scale and over the last 40 years. We used aerial data obtained from suction traps between 1978 and 2015 on five aphid species varying in their degree of specialization to legumes, along with climate, legume crop area and geographical data. Effects of environmental and geographical variables on aphid annual abundance and spring migration dates were analyzed using generalized linear mixed models. We found that within the last four decades, aphids have advanced their spring migration by a month, mostly due to the increase in temperature early in the year, and their abundance decreased by half on average, presumably in response to a combination of factors. The influence of legume crop area decreased with the degree of specialization of the aphid species to such crops. The effect of geographical variation was high even when controlling for environmental variables, suggesting that many other spatially structured processes act on aphid population characteristics. Multifactorial analyses helped to partition the effects of different global change drivers. Climate and land-use changes have strong effects on aphid populations, with important implications for future agriculture. Additionally, trait-based response variation could have major consequences at the community scale

AphidInnov - Des solutions biologiques adaptées pour le contrôle des populations de pucerons des cultures protégées

Alternatives aux néonicotinoïdes Rendu des projets réunissant des contributions des projets scientifiques d'Ecophyto et du Plan National de Recherche et Innovation-betterave avec, selon les projets, les soutiens financiers de l'Office français de la biodiversité (OFB), l’Institut national de recherche pour l'agriculture, l'alimentation et l'environnement (INRAE) et de l'Institut technique de la betterave (ITB).National audienceInundative biological control with natural enemies produced by specialized companies is the main alternative to insecticides in protected crops. However, major pests such as aphids are still poorly controlled, due to a lack of efficiency or availability of biological control agents that would give solutions for the disappearance of neonicotinoids. The AphidInnov project has shown, on seed cabbage, strawberryand cucumber crops, that effective parasitoid species and populations adapted to each agricultural situation could be selected, taking into account the ecological specialization of parasitoids and their genetic variation, and that effective solutions could be proposed by combining parasitoids, predators and cultural practices. The production of these beneficials could release on new business models, involving more directly professional organizations and growers.La lutte biologique par lâchers d'auxiliaires produits par des entreprises spécialisées est la principale alternative aux insecticides en cultures sous abri. Des ravageurs majeurs comme les pucerons restent cependant mal contrôlés, par manque d'efficacité ou de disponibilité des auxiliaires qui permettraient de pallier la disparition des néonicotinoïdes. Le projet AphidInnov a montré, sur culture de choux porte-graines, de fraises et de concombre, que des espèces et populations de parasitoïdes adaptées à chaque situation pouvaient être sélectionnées, en considérant la spécialisation des parasitoïdes et leur diversité génétique, et que des solutions efficaces pouvaient être proposées en combinant parasitoïdes, prédateurs et pratiques culturales. La production de ces auxiliaires pourrait faire appel à des modèleséconomiques nouveaux, impliquant plus directement les filières et les agriculteurs

AphidInnov -Biological solutions for controlling aphid populations in protected crops

Alternatives aux néonicotinoïdes Rendu des projets réunissant des contributions des projets scientifiques d'Ecophyto et du Plan National de Recherche et Innovation-betterave avec, selon les projets, les soutiens financiers de l'Office français de la biodiversité (OFB), l’Institut national de recherche pour l'agriculture, l'alimentation et l'environnement (INRAE) et de l'Institut technique de la betterave (ITB).International audienceInundative biological control with natural enemies produced by specialist suppliers is the main alternative to insecticides in protected crops. However, major pests such as aphids are still poorly controlled, due to a lack of efficiency or availability of biological control agents that would give solutions for the disappearance of neonicotinoids. The AphidInnov project has shown, on seed cabbage, strawberry and cucumber crops, that effective parasitoid species and populations adapted to each agricultural context could be selected, taking into account the ecological specialisation of parasitoids and their genetic variation, and that effective solutions could be proposed by combining parasitoids, predators and cultural practices. The production of these biological control agents could create new business models, involving more directly professional organizations and growers