Sexual dimorphism of arrestment and gregariousness in the bed bug (Cimex lectularius) in response to cuticular extracts from nymphal exuviae

Abstract

Releaser pheromones have direct behavioural effects to arrest, attract or disperse insects, whereas interactions within groups of social insects are often influenced by primer pheromones. The behaviour of insects displaying intermediate levels of sociality is largely unexplored in this context. In the present study, both the gregariousness and arrestment (settling near the odour source) of bed bugs Cimex lectularius L. (Hemiptera: Cimicidae) in response to conspecific exuvial extracts are described. Adult males are arrested on filter papers with extracts derived from exuviae of fifth-instar nymphs. Adult females and nymphs display no significant evidence for such behaviour. Adults of both sexes show no preference for extracts of male versus female fifth-instar exuviae. Arrestment of adult males does not occur on papers treated with fourth-instar exuvial extracts. Because the insects are assayed behaviourally in groups, an index is calculated describing how far bugs are away from being located independently of one another, as a measure of gregariousness. Adult males have lower values for this index (i.e. locations are closer to independence). Adult females, nymph cohorts and mixed age groups all have higher values for this index, which tend to increase over time. Females exhibit a clear increasing dose-dependent relationship for this index. It is concluded that the extracts of fifth-instar nymphal exuvia arrest males on refuges that possess the odour source. However, gregariousness is induced in females, without evidence of a tendency to assemble near the odour source.