Coexistence and Competition betweenTomicus yunnanensisandT. minor(Coleoptera: Scolytinae) in Yunnan Pine

Competition and cooperation between bark beetles, Tomicus yunnanensis Kirkendall and Faccoli and Tomicus minor (Hartig) (Coleoptera: Scolytinae) were examined when they coexisted together in living Yunnan pine trees (Pinus yunnanensis Franchet) in Yunnan province in Southwest China. T. yunnanensis bark beetles were observed to initiate dispersal from pine shoots to trunks in November, while the majority of T. minor begins to transfer in December. T. yunnanensis mainly attacks the top and middle parts of the trunk, whereas T. minor mainly resides in the lower and middle parts of the trunk. The patterns of attack densities of these two species were similar, but with T. yunnanensis colonizing the upper section of the trunk and T. minor the lower trunk. The highest attack density of T. Yunnanensis was 297 egg galleries/m2, and the highest attack density of T. minor was 305 egg galleries/m2. Although there was significant overlap for the same bark areas, the two species generally colonize different areas of the tree, which reduces the intensity of competition for the relatively thin layer of phloem-cambium tissues where the beetles feed and reside