No genetic divergence between contrasted overwintering strategies of a major pest predator Episyrphus balteatus (Diptera: Syrphidea): implications for biocontrol

Background/Question/Methods

Winter ecology of natural enemies has a great influence on the level and efficiency of biological control at spring. The hoverfly Episyrphus balteatus (DeGeer) (Diptera: Syrphidae) is one of the most important natural predators of crop aphids in Europe. Three different overwintering strategies coexist in this species which makes it a good model in order to study ecologically-based speciation processes. The purpose of this study was to determine whether E. balteatus populations with alternative overwintering strategies are genetically differentiated. To that aim, we developed 12 specific microsatellite markers and evaluated the level of genetic differentiation between E. balteatusfield populations that overwinter in the three different ways described in this species (i.e. migration, local overwintering at pre-imaginal stage, and local overwintering at adult stage).

Results/Conclusions

Results showed no genetic divergence between individuals with different overwintering strategies although there are strong ecological differences between them. All pair-wise F_st values are below 0.025 and are non-significant, and Bayesian clustering showed K = 1 was the most likely number of genetic clusters throughout our sample. The three overwintering strategies form one unique panmictic population. This suggests that all the individuals may have genetic material for the expression of various overwintering phenotypes, and that their commitment in one particular overwintering strategy may depends on environmental and individual factors. Consequently, the prevalence of the different overwintering strategies would be potentially modified by ecological engineering and habitat management. The part of population locally overwintering could be increased by providing habitats and trophic resources in order to reduce the dependence on spring arrival of immigrants for aphid biological control.