Overwintering Strategy of Multicolored Asian Lady Beetle (Coleoptera: Coccinellidae): Cold-Free Space as a Factor of Invasive Success

Successful overwintering of a coccinellid species is partially dependent on quality of hibernacula, for surviving cold temperatures, for drowning risk, and for avoiding parasitism or infection by pathogens. The multicolored Asian lady beetle, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), an introduced species that has spread throughout North America since 1988, overwinters outside and inside houses or artificial structures. Five experiments were conducted during winter 2003–2004 to evaluate winter survival of the invasive H. axyridis compared with the indigenous Coleomegilla maculata lengi Timberlake outside and inside human houses, to assess its contribution to the invasive success of the multicolored Asian lady beetle. We formulated the hypothesis that H. axyridis will survive during winter inside human houses and that no survival would be observed outside in Quebec, Canada. Survival of H. axyridis ranged from 25 to 53% in different experiments inside houses, whereas no survival was recorded outside. C. maculata did not survive inside houses, but 12.5% of the individuals survived outside. The indigenous species C. maculata had higher proportion of lipids than the invasive species H. axyridis, suggesting that H. axyridis is not physiologically adapted to overwinter in Canada. Selection of human houses as overwintering sites by the multicolored Asian lady beetle may constitute a “cold-free space,” which could explain its great invasive success in northern regions.