Tactile stimuli trigger group effects in cockroach aggregations

In many gregarious species, social interactions among group members have such a potent influence on the physiology and/or the behaviour of individuals that isolation has dramatic consequences for their development and survival. Although 'group effects' have been described in many insect species, the mechanisms involved in these processes remain poorly documented. Our aim was to shed light on group effects in cockroaches by investigating the nature of the social stimuli triggering differences in developmental rates between grouped and isolated individuals. Group effects were absent in nonaggregating species (Blattella lituricollis, Blattella biligata), but present in species that form social aggregations (Blattella germanica, Symploce pallens). The presence of conspecifics increased rates of both nymphal development and oothecae production in B. germanica. Tactile stimuli were sufficient to trigger developmental group effects in this gregarious cockroach. Blattella germanica nymphs reared with tactile stimuli, either from a rotating feather or from insects of other species, grew faster than isolated nymphs. Although the role of tactile stimuli has been understudied, they could be involved in group effects in many insect species. (c) 2008 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.