Seasonal development of the dark spectacle Abrostola triplasia (L.) (Lepidoptera, Noctuidae) and its environmental control

The paper focuses on the influence of the day length on larval and pupal development of the dark spectacle Abrostola triplasia (Lepidoptera, Noctuidae: Plusiinae, Abrostolini) in the central European Russia (50°N, 36°E). The long-day qualitative photoperiodic response of diapause induction controls formation of the winter pupal diapause and determines a bivoltine seasonal cycle of the species in the forest-steppe zone. Seasonal development of the local population of A. triplasia has the following peculiarity: if adults of the overwintered generation emerge late (in the second half of June), larvae of the first generation develop under the critical, or threshold, daylength conditions, which results in the presence of both diapausing and non-diapausing fractions of the pupae. The diapausing pupae overwinter, whereas the non-diapausing ones develop into adults that produce the second generation; the pupae of this second generation overwinter. Therefore, the hibernating population of A. triplasia consists of individuals from both generations. Thus, the dark spectacle has a very flexible seasonal development pattern in the forest-steppe zone: the presence of two generations allows the species to fully utilize the resources of the vegetation season; at the same time, the first generation already has a reserved hibernating fraction in case the weather conditions of the particular year are not favorable for completion of two generations.