Biotic Factors Affecting Overwintering Population of Pissodes punctatus (Coleoptera: Curculionidae) in Northeast Yunnan Province of China

The mortality rate of overwintering population of the pine bark-weevil, Pissodes punctatus and causes of mortality were examined on newly infested host trees in Northeast Yunnan Province of China. The authors have found an 80.76% mortality rate of P. punctatus, that was greatly higher than the healthy (survival) rate. Life stages of overwintering population of this pest were overlapping including older larvae (3rd-4th instar) (71.20%), pupae (16.47%) and adults (12.32%). The causes of mortality were identified into different biotic factors, which included woodpecker predation, parasitism by insect parasitoids, tree resistance and undetermined diseases. Predation by woodpeckers (41.83%) was the dominant factor causing the mortality of immature stages of P. punctatus and significantly higher than the parasitism by insect parasitoids (18.99%), tree resistance (17.97%) and undetermined diseases (1.98%). Moreover, three hymenopteran ectoparasitoids (Triaspis sp., Rhopalicus sp. and Eurytoma sp.) were observed to attack immature stages of P. punctatus. Relevance of these findings to biological control associated with forest management of P. punctatus was discussed.