Agonistic Tactics and Size Asymmetries between Opponents in Blattella germanica (L.) (Dictyoptera: Blattellidae)

In this paper we investigated the influence of size differences between opponents on the occurrence of different agonistic attack and response tactics displayed during encounters between Blattella germanica (L.) cockroaches of all developmental stages, competing for a limited food source. The two main results were: 1) attack and response tactics varied during development and 2) size asymmetries between contestants influenced agonistic tactics. Developmental stage of initiator influenced the frequency distribution of the three types of attack patterns (Bite, Kick and Jump) and of the four types of response patterns (Retaliation, Escape, Resettle and No Response). The proportion of kicks increased gradually with developmental stage of the initiator whereas the proportion of bites declined during development. In addition, cockroaches adapted their attack tactics to the developmental stage of their opponent. Similarly the response displayed varied in relation to the developmental stage of the attacked individual, the developmental stage of the initiator and the type of attack displayed. During an interaction, animals appeared to be able to evaluate the relative size of their opponent and to evaluate the consequences of the behavioural pattern they displayed. Larger animals tended to minimize the intensity of the agonistic act they initiated. Escalation in interactions was rare and smaller individuals tended to escape when attacked by larger ones. Wrong estimations of the relative size of opponent, when a smaller animal retaliated after being attacked by a larger animal or when a larger animal fled after being attacked by a smaller one, represented only 6% of the records.