Aggregation behavior of Harmonia axyridis under non-wintering conditions

The invasive multicolored Asian ladybeetle, Harmonia axyridis (Pallas)
(Coleoptera: Coccinellidae), aggregates inside dwellings during winter to avoid cold
weather. This adaptive behavior disturbs homeowners, because of the large numbers of
individuals that aggregate, which induces allergic reactions. The migratory flight patterns
of this species have been well documented, with individuals preferentially moving toward
prominent and high color contrast elements. However, the factors involved in the selection
of aggregation sites by this species have yet to be elucidated. Here, we evaluated the influence
of (i) the density of individuals and (ii) the type of available shelters on decisions by
H. axyridis to settle and aggregate under shelters. A dual choice bioassay conducted in the
laboratory demonstrated the presence of mutual attraction to conspecifics. We also found
that individuals preferentially settled under red covered shelters compared to transparent
shelters, and that the type of shelter outweighed the effect of social interactions among
conspecifics. Moreover, this experiment was performed under non-wintering conditions,
providing the first evidence that aggregative behavior in this species can also occur under
those specific conditions.