Recolonisation of an apple orchard by leafrollers (Lepidoptera: Tortricidae) following spraying

The recolonisation of a 2.2 ha apple block by three leafroller species was studied in autumn in each of 2 years, 1-4 months after an intensive organophosphate insecticide programme finished. Two transects at right angles, each bisecting the block, were set up with 16 stations located 0-40 m in from each side and one in the centre. Between 60 and 80% of larvae, shoot damage, pheromone and molasses bait trap catches were recorded within 10 m of the outermost trees. The presence of leafroller-hosting trees adjacent to the orchard had a major influence on the spatial pattern of infestation. Adult leafrollers were trapped throughout the study, but few larvae and little shoot damage appeared until 3-4 months after spraying stopped. Ctenopseustis obliquana (51%) and Planotortrix octo (44%) comprised the majority of larvae. Compared with these proportions, catches in bait and pheromone traps under-represented C. obliquana, but over-represented Epiphyas postvittana. Almost 4 months after spraying ended, the parasitism rate (3%) and parasitoid species diversity had not recovered to levels at sites where organophosphates were not used. The implications of these results for current integrated fruit production practices are discussed.