Seasonal abundance of exotic leaf beetle Orphraella communa LeSage (Coleoptera: Chrysomelidae) on two different host plants

Insects sometimes invade different habitats in new territory compared to their original habitat. In the present study, the seasonal abundance of an exotic leaf beetle, Ophraella communa LeSage (Coleoptera: Chrysomelidae), which invaded Japan from North America in 1996, was investigated from April to October 2003 on two host plants, the common ragweed Ambrosia artemisiifolia L., and the giant ragweed A. trifida L., in Okayama City, Japan. Two peaks of population abundance were found on both plants within the year. Many O. communa were found on A. trifida growing on a hill area (land), whereas no insects were found on A. trifida growing on the bank of a riverbed (river), where the plants occasionally suffered water inundation. More pupae were found on the underside of plant leaves than on the surface of leaves, stems, and flowers; however, the pupation sites of the plants differed in September. No parasitoid or fungus was found in the laboratory and field, but predators were observed in the field in 2003, the fifth year after O. communa invaded Okayama. The results showed that the beetles fed on A. artemisiifolia as well as A. trifida in Japan, which is not reported as a host plant at their origin.