Invasion, dissemination, increase of density and seasonal trend of occurrence of the rice water weevil, Lissorhoptrus oryzophilus KUSCHEL in Fukuoka Prefecture.

Invasion of the rice water weevil (Lissorhoptrus oryzophilus KUSCHEL) in Fukuoka Prefecture was first confirmed in June 1983. The occurrence was limited to only five paddy fields on the small island of "Oshima" and 9 adult weevils were collected in 15a paddy fields in the first survey. In the following year, however, the weevil spread to the whole area of the island, and the adults were observed in paddy fields as far as 1.6 km apart from the sites where they first occurred. In the same year the weevil occurred in Shingu town and Iizuka city. Shortly after transplanting was performed on May 8, overwintered adults invaded the paddy fields and started to infect rice seedlings. Adult density increased rapidly to reach a peak at the end of May, but it decreased rapidly in early June. Two-year survey on Oshima island showed that the weevil maintained a high reproductive rate in the years immediately after the initial invasion.