Restricted diet prevents the induction of diapause in Trichogramma larvae

Abstract

Photoperiodic and thermal diapause-inducing responses of insect parasitoids are well known whereas the trophic response is rather poorly studied. Our experiments showed that restricted diet prevented the induction of diapause in Trichogramma telengai parasitizing the grain moth (Sitotroga cerealella) eggs. In particular, the incidence of diapause decreased (1) with the rate of superparasitism (parasitoid:host ratios of 1:50, 1:25, 1:10, and 1:2 were tested), (2) with the time of host storage at 5 °C (0, 20, 40, 60, and 80 days), and (3) with host embryo development (1, 3, 5, 7, and 9 days at 20 °C). Both changes in the initial proportions of diapause-destined and non-diapause-destined individuals and differential mortality in these two categories were observed. These effects are most probably based on high nutritional demands of diapause-destined individuals: restricted diet causes nutrients deficiency and thereby prevents diapause. For the practice we conclude that if the induction of diapause for cold storage of mass or laboratory reared Trichogramma species is planned, host quality requirements should be tightened.