Multigenerational maternal effect on diapause induction in Trichogramma species (Hymenoptera: Trichogrammatidae)

Maternal photoperiodic response is known to influence the percentage of diapausing prepupae in Trichogramma species. However, the influence of several preceding generations has not yet been studied. We have investigated the stability of photoperiod-induced changes in multiple generations of Trichogramma buesi Voegele and Trichogramma principium Sug. et Sor. Short-day conditions during preimaginal development induced an increase in the percentage of diapausing progeny and grand progeny of both Trichogramma species. A similar trend was also detected in the fourth and fifth generations, but the response was weak although statistically significant. This grand-grandmaternal photoperiodic effect (which has not been demonstrated before for Trichogramma or for any other insect parasitoid) is most probably based on the transgenerational transmission of variations in DNA expression. We conclude that in mass rearing, to facilitate diapause induction before cold storage, it is advisable to rear both maternal and grandmaternal generations under the short-day conditions. In scientific studies, several generations preceding the experiment should be kept under equal conditions to exclude multigenerational maternal effects.