Abstract: Tomicus minor (Hartig) is one of major secondary pest insects of the Yunnan pine, Pinus yunnanensis Franchet. From the 1980's, the pine shoot beetle together with T. piniperda (L.) occurred in abundance in Yunnan, southwestern China, causing several hundred thousand ha Yunnan pine forests seriously damaged. The biology and behavior of the beetle were reported here, including its life cycle, development, shoot feeding, trunk attacking and reproduction. T. minor completed one generation a year, with consecutive two generations overlapping in winter and spring. Adults started to emerge in the mid April and ended in the late May. After emerged, T. minor flied to the crown and fed the shoots in nearby trees. The shoot feeding period lasted until the late November when adults got matured. Adults bored 4-6 shoots in total during the shoot feeding. T. minor flied to the trunk of Yunnan pine tree for reproduction after matured. The reproduction period lasted from the late November to March. T. minor mostly bred in the trees already attacked by T. piniperda. The attacking normally occurred one week later than T. piniperda, and focused on the mid and lower trunks. Since the beetle did its damages from the shoots to trunks, the damages to the host trees seemed more serious than that in other districts. Meanwhile, T. minor breeding in the trees attacked by T. piniperda would decrease the tree resistance, and so accelerate the host tree dying. The beetle's bionomics and behavior particularly showed in Yunnan were supposed to the major reason that the beetle occurred massively and caused serious damages to the Yunnan pine trees in southwestern China. A fungus Leptographium yunnanensis was detected from T. minor and its galleries, which was regarded as the fungus associated with T. minor. Frequencies of the beetle carrying the fungus were 11.5% in shoot feeding period, and 10%-26% in trunk attacking.

Key words: Tomicus minor, Tomicus piniperda, Pinus yunnanensis, blue stained fungus, biology