Observations on the seasonality of Diapria conica (Fab.) (Hymenoptera: Diapriidae), a pupal parasitoid of Eristalis tenax (L.) (Diptera: Syrphidae), and implications for mass-rearing for pollination

Hover flies, particularly widely-distributed, large-bodied species like the drone fly (Eristalis tenax), show promise as managed crop pollinators, with work underway in multiple continents focused on mass-rearing them for pollination. Parasitoids can be problematic in insect mass-rearing, as high densities of hosts can promote rapid growth of parasitoid populations. The endoparasitoid Diapria conica has occasionally been reported attacking pupae of E. tenax, but relatively little is known about it, making its potential threat to E. tenax mass rearing difficult to assess. In this study, we reared E. tenax following established protocols, and report seasonal trends in E. tenax and parasitoid emergence. Highest parasitoid numbers were observed in the autumn. Overall parasitism rates varied, with population peaks and regional differences that need to be accounted for in mass-production systems. These variations may impact not only rearing success, but released populations and their pollination contribution, as high parasitism rates were accompanied by high failure to eclose from apparently healthy pupae. This preliminary observational study underscores the importance of considering parasitoids in developing E. tenax for large-scale managed pollination, while emphasising the need for further research to fully understand the implications for commercial pollination services.