Period of adult activity and response to wood moisture content as major segregating factors in the coexistence of two conifer longhorn beetles, Callidiellum rufipenne and Semanotus bifasciatus (Coleoptera: Cerambycidae)

The cerambycid borers Callidiellum rufipenne (Motschulsky) and Semanotus bifasciatus (Motschulsky) infest coniferous logs in Japan, with the latter distributed in the north and at high altitudes, where both species occur sympatrically. Semanotus bifas- ciatus adults were active at low temperatures and very active after sunset, and less active but never inactive in the daytime, whereas C. rufipenne adults were usually active at high temperatures and almost only in the daytime. At an almost constant temperature, C. rufipenne adults were almost inactive at night, whereas S. bifasciatus adults showed only an obscure decline in activity in the morn- ing. Of a horizontal log, the upper surface tended to be drier and lower surface wetter, and C. rufipenne larvae grew large if they were in the upper part of a log, whereas S. bifasciatus larvae grew large if in the lower part. Thus, the coexistence of these two spe- cies can be ascribed to two major segregation factors: adult segregation based on temperature and sunshine, and larval segregation associated with the moisture content of the wood.