Environmental Entomology (1998) 27, 578-582

R.G. Van Driesche, J.L. Mason, S.E. Wright and R.J. Prokopy (1998)
Effect of reduced insecticide and fungicide use on parasitism of leafminers (Phyllonorycter spp.) (Lepidoptera: Gracillariidae) in commercial apple orchards
Environmental Entomology 27 (3), 578-582
Abstract: Development of alternative controls (i.e., 2nd-level insect pest management [IPM] methods) for apple maggot [Rhagoletis pomonella (Walsh)] that reduce pesticide use is in progress. The current project was undertaken to see if such controls would better conserve natural enemies of pest leafminers (Gracillariidae, Phyllonorycter spp.) when applied over a large physical scale, as compared with results in earlier studies with smaller plots. Second-level IPM in apple, Malus pumilla Miller, orchards may consist of substitution of either use of red sticky spheres in border rows or border-row pesticide applications for control of apple maggots rather than cover sprays of insecticides over entire orchard blocks. We previously established that 2nd-level IPM increased parasitism rates in tissue-feeding larvae of 2nd generation Phyllonoryeter 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 1st-level IPM. We hypothesized that conservation of leafminer parasitoids would improve when 2nd-level IPM was applied to entire orchard blocks (1.6-3.6 ha) because conflicts with pesticides used in adjoining areas (drift into untreated areas and parasitoid movement into treated areas) would decrease. Results of our test did not support this hypothesis. We determined that benefits of 2nd-level IPM were the same in 1.6-3.6-ha blocks as in 0.4-ha plots. In both types of plots, parasitism increased only when trapping, not border sprays, was used to manage apple maggot, and benefits occurred only in the 2nd host generation. No carryover of benefit to the 3rd generation in the same year, or to the 1st generation of the following year, could be detected. Elimination of fungicide use (in disease-resistant blocks) increased leafminer parasitism. Although most parasitism was due to eulophid parasitoids, the proportion of total parasitism caused by braconids was greatest under 2nd-level IPM, suggesting that reduced pesticide use was especially beneficial to this parasitoid group. These findings suggest that 2nd-level IPM methods for apple maggot control have only a limited ability to conserve leafminer parasitoids, regardless of plot size. Furthermore, our findings suggest use of fungicides on apple orchards may be harmful to leafminer parasitoids.
(The abstract is excluded from the Creative Commons licence and has been copied with permission by the publisher.)
Database assignments for author(s): Roy G. Van Driesche

Research topic(s) for pests/diseases/weeds:
biocontrol - natural enemies
control - general
Research topic(s) for beneficials or antagonists:
resistance to pesticides

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Phyllonorycter (genus)	Apple (Malus)