Effects of Color Morph on Aggregation Formation for Hibernation in an Extremely Color Polymorphic Ladybug, Harmonia Axyridis (Pallas) (Coleoptera: Coccinellidae)

Understanding of mechanism for genetic polymorphisms within and among species is an important issue in ecology and evolutionary biology. A ladybug, Harmonia axyridis (PALLAS), shows extreme elytral color polymorphism, in which more than 100 types have been recognized. This polymorphism has been explained with the inheritance of 12 hypothetical alleles at a single autosomal locus. However, why such extreme polymorphism is maintained has not been clarified. Here, we show that several morphs enlarge their aggregation size during grouping before hibernation. Our results showed that the excess (or fewerness) of either one of the four color morphs from the expected values showed each a significantly positive effect on the aggregation size. A larger aggregation size resulted in better survival of all the aggregating members. These results suggest that it is beneficial for survival to aggregate with these morphs. This survival benefit during hibernation explains partly the extreme color polymorphism in this species.