Thermoperiodic Effect on Diapause Induction in the Progeny of Female Trichogramma telengai Sor. (Hymenoptera, Trichogrammatidae): Adjustment but not Substitution of Photoperiodism

The effects of constant temperatures (15, 20, 25, and 30°C) and thermoperiods (daily alternations of high temperature of 25 or 30°C and low temperature of 15 or 20°C) on maternal induction of diapause in the offspring of egg parasitoids Trichogramma telengai Sor. (Hymenoptera, Trichogrammatidae) was studied. Each combination of temperatures was tested in two variants: “short-day” (with the periods of high and low temperature lasting 12 h) and “long-day” (with the periods of high and low temperature lasting 18 and 6 h, respectively). In addition, constant temperatures equal to the thermoperiod means were tested. The experiments showed that thermoperiods and constant temperatures significantly influenced diapause induction in the T. telengai progeny, both in interaction with different photoperiods and under conditions of constant darkness. However, thermoperiods do not seem to convey information on day length and are unlikely to serve as seasonal cues in Trichogramma .