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. We 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. Triaspis sp. was the dominant species amounting 70.59% of the parasitoids, indicating a high potential in the biological control programme of P. punctatus. Relevance of these findings to biological control associated with forest management of P. punctatus was discussed.
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