Social interactions during development in the ovoviviparous cockroach Schultesia lampyridiformis

Abstract Cockroaches are generally divided into solitary and gregarious species. Schultesia lampyridiformis (Zetoborinae) is a neotropical cockroach presenting unusual characteristics: it inhabits only pendulous nests of colonial Cacicus birds and feeds on broken eggs or bird corpses. This patchy habitat and food resource was expected to favour gregarious habits, which were effectively observed in adults. However, young nymphs dispersed during the first hours following birth. The gregarious life style should thus appear during the course of nymphal development. This study is aimed at specifying the timing of apparition of gregariousness during the development, and identifying the behaviours characterising the solitary and gregarious phases. We compared under experimental conditions social interactions and spatial distribution in pairs of nymphs at different instars (1, 2, 3, 5 and last instar) and in pairs of adult females. The gregarious phase appeared progressively in the last nymphal instars, and was characterized by a simultaneous increase in several behavioural features: length of interaction sequences, proportion of mutual antennal contacts, rate of answer to social stimulations from conspecifics and proportion of time spent close to conspecifics. This behavioural change is discussed regarding its possible function and importance for comparative studies of gregariousness.