Diel asynchrony in reproductive behaviour of diaeretiella rapae (m'intosh) (hymenoptera: aphidiidae)

Abstract

Diaeretiella rapae is an important parasitoid of cabbage aphid. Diel variation in emergence, mating and oviposition of D. rapae was studied in the laboratory to understand the biology and behaviour of the parasitoid. The emergence of the parasitoid was recorded hourly in two bioassay rooms set up at 22 ± 2°C with 16 h photoperiod from 0800-2400 hours or from 1800-1000 hours. Greatest emergence was found during the early photophase. The parasitoids that emerged during the scotophase did not mate until the following photophase. Unmated females that emerged during the scotophase had a lower incidence of host attack and oviposition during the dark. However, the parasitoids became active and had a greater incidence of mating and oviposition when they were brought into the light even during the scotophase. This research suggests that light triggers parasitoid activity and that the parasitoids lose their reproductive fitness if they emerge in the scotophase.