Integrated control of apple pests in New Zealand

Abstract

For six generations, 5th‐instar larvae of the codling moth (Laspeyresia pomonella) which had finished feeding in apples were tagged externally with cobalt‐58 and released on ‘Delicious’ trees, where they sought cocooning sites. The larvae were released according to their natural distribution in fruit in the trees and on the ground. Most larvae left the fruit between 90 and 210 cm above the crotches of the trees, and their distribution on the leaders was aggregated.The distribution of cocoons formed by the tagged larvae revealed net larval movement after release. Most cocoons were formed under bark (19.9 %), in natural holes and depressions (17.9%), and around pruning scars (13.4%) and spurs (15.2%). Maximum cocoon densities occurred between 60 and 150 cm above the crotch and on the trunk. Only 3.8% of cocoons were formed on the ground and 21.6% on the trunk and basal 60 cm of the main leaders, compared with 74.7% above this level. The cocoons were aggregated on the leaders and within individual sites, and most larvae appeared to spin up on the leader on which they were released. More cocoons occupied sites facing south than north, and within the trunk area the number of cocoons increased towards the base.Larvae in cocoons under bark and in large holes died from disease more frequently than larvae in other sites. Bird predation, by the silvereye (Zosterops lateralis), was influenced by the distribution of cocoons; predation increased with the height of cocoons in the trees and with increasing exposure of the different site types. The birds fed on the cocooned larvae mainly from May to August.The larval and cocoon distributions are discussed in relation to other published distributions and to descriptions of codling moth cocooning behaviour. The responses of silvereyes to cocoon density and distribution are compared with those of other known bird predators of the codling moth.