Overwintering features of Drosophila parasitoids (Hymenoptera) in a temperate region of Japan

Overwintering features of Drosophila parasitoids were studied in a temperate region of Japan, in an outdoor rearing experiment conducted from autumn to spring. Eight taxa, Asobara japonica, A. leveri, A. brevicauda, Leptolamina sp. TK1, Leptopilina tsushimaensis, Leptopilina japonica japonica, Ganaspis lupini and Trichopria drosophilae, were collected in this study. Among them, the first five emerged in spring, suggesting that they overwintered in diapause at the preimaginal stage. In the three Asobara species, however, a number of individuals emerged as adults in autumn and all of them died by mid-winter. We assessed whether the most abundant A. japonica emerging in autumn can leave offspring that survive the winter based on estimates of the lower developmental threshold and effective temperature for larval development, as well as local temperature conditions. The results suggest that the eggs laid after mid-October may not survive the winter and that the emergence of A. japonica after mid-October may not be adaptive. While it has been reported that Leptopilina japonica japonica also enters prepupal diapause, only one individual was collected, and therefore its overwintering features are not apparent in this study. As for the remaining species G. lupini and T. drosophilae, the outdoor rearing and experiment using laboratory strains suggest that they have limited overwintering capacity: the winter survivorship of adults was 14.3% and 4.1%, respectively; no G. lupini and only one individual of T. drosophilae emerged in spring; and both did not enter diapause at the preimaginal stage under short daylength in laboratory.