Study of the factors involved in the aggregation of Harmonia axyridis Pallas (Coleoptera : Coccinellidae)

The aggregative behaviour of the multicoloured Asian ladybeetle, Harmonia axyridis Pallas, during winters, is still misunderstood. Our study was focused on the chemical and physical factors involved in the selection of its aggregation sites. Chemical and behavioural analyses highlighted that long-chain hydrocarbons lead congeners towards aggregations and ensure the cohesion of the cluster. On the other hand, we investigated the influence of (1) the density of individuals and (2) the quality of available shelters on H. axyridis decision to settle and aggregate under shelters. A binary choice experiment conducted in laboratory highlighted a permanent aggregative behaviour of H. axyridis, even during non-wintering conditions, and the existence of social interactions between individuals.