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

Abstract

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.