A field experiment on dispersal of newly emerged adults ofMonochamus alternatus (Coleoptera: Cerambycidae)

Newly-emerged adults of Monochamus alternatus aged 1 to 5 days were code-numbered with lacquer paint and released by placing them on the trunks of one or two trees in a Pinus thunbergii stand at weekly intervals during the beetle emergence period from 1980 to 1983. Beetles were captured at weekly intervals from one week after the first day of release. Determinations were made on the distance and direction of beetle dispersal during a week after release and analysed by a method of Inoue (1978). When the stand canopy was closed, the rate of beetle's stay on trees was 0.56 per week. The beetles dispersed at random by walk and flight. When the pine stand was sparse, the rate of beetle's stay on trees was 0.02–0.30 per week. They dispersed at random by flight. The average distances traversed were estimated to be 7.1–37.8 m for the first week after emergence. Using other method, the average distance traversed was estimated to be 10–20 m for each week through the first 3 weeks after release. The results of stepwise multiple regression analysis and a simple field experiment suggested that the dispersal of newly-emerged beetles was affected by stand density, number of beetles emerging from individual dead trees, maximum air temperature, and precipitation.