How does host quality affect oviposition rate and diapause in sexual and asexual Trichogramma brassicae?

The egg parasitoids of the genus Trichogramma have become one of the most important economic insects, for they are widely used in biological control of Lepidopteran key pests. For that reason, all aspects of their mass production including diapause have been considered over the last few years. In this study, the effect of host quality on the diapause induction of sexual and asexual T. brassicae Bezdenko (Hym: Trichogrammatidae) have been investigated at two temperatures. Maternal generation developed at two distinct temperatures (14 and 20 °C) and they oviposited on four different qualities of Ephestia kuehniella Zeller (Lep: Pyralidae) eggs including fresh eggs, frozen eggs, host eggs with developing embryo and low quality eggs. Data analysis revealed significant influence of temperature and host quality on diapause induction in both sexual and asexual strains. Maximum diapause happened in host eggs with developing embryo even though they were in fetal development. A higher level of diapause was observed in T. brassicae whose maternal generation had developed at 20 °C. The diapause induction in asexual T. brassicae was less than sexual wasps. The results imply that Wolbachia causes a disturbance in the diapause process. The outcomes of this study, which are new, indicate the complexity of diapause and the importance of factors such as host quality which have received less attention in diapause induction.