Seasonal Changes in Numbers and Distribution Patterns of Pine Bark Weevils : Shirahoshizo spp. : (Coleoptera : Curculionidae) Attracted to Pine Bait Logs

抄録

The seasonal changes in number of adults attracted to Japanese red pine (Pinus densiflora) bait logs were observed for the pine bark weevils, Shirahoshizo spp. (including S. pini, S. rufecens and S. insidiosus). From the dissection of the males collected on bait logs, almost all were S. rufecens. The ration of the number of adults in copulation to the total number observed on the bait log indicated that the adults of Shirahoshizo spp. seemed to copulate more frequently on thick bark conditions than thin bark ones. Flying weevils were attracted for about one and one-half months. The seasonal changes in number of attracted adults on each bait log showed some similarities among some bait logs. The corrrelation coefficients of these fluctuation patterns between each bait log were calculated. Although the attracted patterns in a group of logs resembling their bark conditions showed similar trend, the dendrogram of these coefficients showed remarkable differences among log groups in these patterns. The contagious distribution pattern of the accumulated number of adults on bait logs showed that the log with thin bark had some unfavourable parts on the surface that the adults avoided in favor of other parts.