Biology of Pissodes yunnanensis (Coleoptera : Curculionidae), a pest of Yunnan pine in southwestern China

摘要

Pissodes yunnanensis Langor et Zhang, a pest of Yunnan pine, Pinus yunnanensis Franchet, in southwestern China, occurs at elevations of 2200-2800 m. These weevils infest Yunnan pine trees less than 20 years old but prefer trees 810 years old. Oviposition occurs mainly along the upper trunk on current-year and 1-year-old growth and occasionally on the upper lateral branches. Weevil feeding often kills the leader, which results in stem forking and crooking. At times, after 23 years of consecutive severe infestation, tree mortality occurs. In southwestern Yunnan Province, adults of this univoltine weevil emerge from infested stems from mid-April to mid-July. Eggs appear in late June, first-instar larvae in early July, and fourth-instar larvae in late March of the next year. First- and second-instar larvae feed in the phloem, and third-instar larvae move to the sapwood or pith, where they overwinter. In March, larvae resume feeding and development. Fourth-instar larvae excavate pupal chambers (chip cocoons) in the outer sapwood or pith, and pupation occurs from late March to late May. Optimal development of eggs and pupae occurs at 25 degreesC in the laboratory. Parasitism is the main cause of mortality in P. yunnanensis, accounting for 2%-25% of mortality among third- and fourth-instar larvae and 5%-10% among pupae.