EFFECT OF REDUCED INSECTICIDE AND FUNGICIDE USE ON PARASITISM OF LEAFMINERS (PHYLLONORYCTER SPP.) (LEPIDOPTERA, GRACILLARIIDAE) IN COMMERCIAL APPLE ORCHARDS

Development of alternative controls (i.e., 2nd-level insect pest manag ement [IPM methods) for apple maggot [Rhagoletis pomonella (Walsh)] th at reduce pesticide use is in progress. The current project was undert aken to see if such controls would better conserve natural enemies of pest leafminers (Gracillariidae, Phyllonorycter spp.) when applied ove r a large physical scale, as compared with results in earlier studies with smaller plots. Second-level IPM in apple, Malus pumilla Miller, o rchards may consist of substitution of either use of red sticky sphere s in border rows or border-row pesticide applications for control of a pple maggots rather than cover sprays of insecticides over entire orch ard blocks. We previously established that end-level IPM increased par asitism rates in tissue-feeding larvae of 2nd generation Phyllonorycte r spp. under trap but not border-row spray management, when tested at the scale of 0.4-ha plots that were part of larger blocks under ist-le vel IPM We hypothesized that conservation of leafminer parasitoids wou ld improve when 2nd-level IPM was applied to entire orchard blocks (1. 6-3.6 ha) because conflicts with pesticides used in adjoining areas (d rift into untreated areas and parasitoid movement into treated areas) would decrease. Results of our test did not support this hypothesis. W e determined that benefits of end-level IPM were the same in 1.6-3.6-h a blocks as in 0.4-ha plots. In both types of plots, parasitism increa sed only when trapping, not border sprays, was used to manage apple ma ggot, and benefits occurred only in the 2nd host generation. No carryo ver of benefit to the 3rd generation in the same year, or to the 1st g eneration of the following year, could be detected. Elimination of fun gicide use tin disease-resistant blocks) increased leafminer parasitis m. Although most parasitism was due to eulophid parasitoids, the propo rtion of total parasitism caused by braconids was greatest under and-l evel IPM, suggesting that reduced pesticide use was especially benefic ial to this parasitoid group. These findings suggest that End-level IP M methods for apple maggot control have only a limited ability to cons erve leafminer parasitoids, regardless of plot size. Furthermore, our findings suggest use of fungicides on apple orchards may be harmful to leafminer parasitoids.