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

Abstract

Citation: Postic, E., A. Le Ralec, C. Buchard, C. Granado, and Y. Outreman. 2020. Variations in community assemblages and trophic networks of aphids and parasitoids in protected crops. Ecosphere 11(5):Abstract. Greenhouse crops are thought to be simplified ecosystems because they often consist of monocultures 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.

Genetics of wild and mass-reared populations of a generalist aphid parasitoid and improvement of biological control

“…In greenhouses where commercial parasitoids were released before sampling, we mostly found ‘wild’ parasitoids. This supports the hypothesis that most parasitism is due to wild individuals rather than released ones, even if greenhouses are relatively closed agroecosystems [ 13 ]. Contrary to several other Aphidiinae parasitoids, using molecular markers, A .…”

“…e . dead aphids containing an immature parasitoid) in strawberry greenhouses in 2017 and 2018, in five regions of France, using the sampling design described in [ 13 ]. For both years, protected strawberry crops were sampled during the spring (from April to May) and the summer (from August to September).…”

“…After emergence, adult parasitoids were placed in 96% ethanol and the parasitoid species was identified using morphological criteria before DNA extraction [ 16 ]. The specific diversity of emerged parasitoids was described in [ 13 ], in the present study only parasitoids identified as Aphidius ervi were considered. Their aphid hosts were also identified based on morphological traits of the mummy [ 17 ].…”

“…ervi coexist, the more frequent being Acyrthosiphon malvae (Mosley), M . euphorbiae and Rhodobium porosum (Sanderson) [ 13 ]. However, spontaneous colonization of greenhouses with A .…”

“…ervi was observed on its three major aphid hosts on strawberry, suggesting that some wild populations of A . ervi would be more effective at controlling aphids in strawberry crops than mass-reared commercial ones [ 13 ].…”