Extremely rapid maternal photoperiodic response in Trichogramma telengai: A fine-scale study

Timing of maternal photoperiodic response of Trichogramma telengai to a single long night was studied in laboratory experiments. Adult females reared under diapause-averting short night conditions (L:D = 18:6) experienced one diapause-inducing prolonged night (12 h) and then were allowed to lay eggs (to parasitize the host, Sitotroga cerealella, eggs) during 3 days. The progeny was incubated under moderately diapause-inducing conditions (14 °C in the dark). The maternal photoperiodic response was extremely rapid: a slight but statistically significant increase in the incidence of diapause was already observed in the progeny hatched from the eggs laid 8 h after the beginning of the 'additional' part of night. Such a quick photoperiodic response, as far as we know, has not been reported for any insect. Then the proportion of diapausing progeny gradually increased over 30-50 h reaching 85-95%. Control females developed and were kept as adults under short night (L:D = 18:6) conditions; diapause was induced in <10% of their progeny. Analysis of individual variations showed that the proportion of diapausing progeny of experimental females increased with time gradually (not abruptly). These data enriches our knowledge of insect photoperiodic response and can be used for the planning of further (in particular, molecular) studies.