Cockroach aggregation based on strain odour recognition

Blattella germanica (L.) cockroaches are gregarious during their resting period. Binary choice tests with groups of larvae indicated a strong tendency to aggregate on a single resting site. This was observed even when all sites were identical or when larvae came from either one or two strains. Previous results showed that gregarious behaviour is mainly based on recognition of cuticular hydrocarbons characterizing strain odour and that larvae prefer their own strain odour to that of another strain. Nevertheless, when groups in tests came from two different strains and had the choice between their two strain odours, they aggregated on only one of the sites. A mathematical model relying on a minimum number of functioning rules was devised to reproduce these experimental collective responses. The model is based on a fundamental parameter representing individual variation in the resting period on a given site in relation to the number of individuals on that site. Taking only this parameter into account, the model predicted that different strains are able to aggregate on the same site despite a weak interstrain interattraction parameter. Blattella germanica is thus an interesting biological model to investigate different aspects of aggregation and interindividual recognition.