Overwintering of Encarsia tricolor on the cabbage whitefly

Abstract: Encarsia tricolor is the dominant parasitoid species of the cabbage whitefly, Aleyrodes proletella. The latter finds sufficient overwintering habitats to appear in masses on cabbage crops during cultivation periods, whereas habitats with suitable overwintering hosts for E. tricolor are hardly available. Therefore, specific management strategies are needed to facilitate parasitoid overwintering. As a first step, this study aimed to provide general knowledge about the overwintering stages, the overwintering period and the overwintering success of E. tricolor on its primary host A. proletella. Results show that Encarsia tricolor successfully survived winter as immature stages, but no adults were found during late winter months. Visual observations revealed that at least 2.4% of A. proletella nymphs actually enclosed vital parasitoid eggs/ larvae during winter (n = 1,603), because they started to turn dark (parasitoid pupation) between 13-20 April. The proportion of adult emergence from these subsequently developed parasitoid pupae was 41%. In contrast, only 1.1% of parasitoid pupae collected in January overwintered successfully (n = 356). First adult E. tricolor were found on yellow sticky traps in the field between 4-11 May. The gained insights on the overwintering of E. tricolor are compared with the population dynamics of A. proletella on cabbage crops and conclusions for additional management strategies are discussed.