Availability and location of cocooning sites for diapausing codling moth larvae (Cydia pomonella (L.)) (Lepidoptera: Tortricidae) on mature and young apple trees

摘要

Mature larvae of the codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), a key pest of apples and pears, leave infested fruit and spin cocoons in which they transform to pupae. These larvae may either immediately transform to pupae from which moths emerge two to three weeks later, or they overwinter in a state of diapause (Headlee 1929; Steiner 1929; Cutright 1937; Gould & Geissler 1941; Yothers & Carlson 1941; MacLellan 1960; Geier 1963; Wearing & Skilling 1975a,b; Howell 1994; Lacey et al. 2006). Cocooning sites are usually in crevices, under loose bark or in the splintered ends of broken branches on the host tree, and sometimes in loose debris on the ground or in the soil around the tree trunk (Steiner 1929; Yothers & Carlson 1941; MacLellan 1960; Geier 1963; Wearing & Skilling 1975a. Geier (1964) studied the population dynamics of codling moth in Australia and concluded that under optimal weather conditions and negligible parasitism, cocoon shelter, together with larval food, are themain factors limiting the abundance of the insect. Since the availability of larval food only becomes restrictive at very high infestation levels, and the mortality of larvae in cocoons spun on the ground is extremely high (Wearing & Skilling 1975a), the number of cocooning sites on the tree becomes the most important factor determining how many individuals will survive the winter and develop into the spring flight of the new season. On young trees with fewer cocooning sites, competition for these sites may be a maj or limitation to codling moth increase (Wearing & Skilling 1975b). This study was undertaken to establish the relative abundance and location of available cocooning sites on young and mature Golden Delicious and Granny Smith apple trees inthe Western Cape of South Africa.