Group formation and dispersal in the German cockroach, Blattella germanica (L.) (Dictyoptera: Blattellidae)

The studies presented here are an effort toward learning about the behavior of small mixed populations of German cockroaches. Of particular interest was the effect of female cockroaches on the behavior of the group, particularly the group formation within a harborage and the dispersal from a harborage. The effect of females was looked at with respect to female density and reproductive state.

Populations aggregated at low female densities. This response increased when densities of gravid females increased but decreased when densities of non-gravid females increased. The effects of female reproductive state on dispersal could not be determined as non-gravid females developed egg cases by the end of the study. Increased female density caused increased dispersal of females and mid-instars. The mid-instars were the primary dispersers in each experiment. Early instars, excluding escapees, dispersed least.

The results of these studies indicate the females of a population can mediate the behavior of that population and its members. It is postulated that this may be achieved by the production and/or regulation of sex, aggregation, and dispersal-inducing pheromones by females.