Non-target impacts of hail netting and insecticides on natural enemy abundance and diversity in a Midwestern U.S. commercial apple orchard

Abstract

A variety of exclusion systems for integrated pest management (IPM) have become viable alternatives to traditional insecticide use in tree fruit production globally. Exclusion netting has been particularly effective as a control strategy for several insect pests of apple. In Minnesota, USA, hail netting, used to protect high-value fruit from hail damage, was recently shown to effectively exclude the two major insect pests: codling moth (Cydia pomonella L.) and apple maggot (Rhagoletis pomonella Walsh). The present study aimed to determine the impact of single-row, drape-style hail netting (DrapeNet®) on the natural enemy community and how this compared to the impact of insecticides used by a Minnesota grower. Sampling occurred during 2021 and 2022 at two orchard locations in Minnesota using yellow sticky traps. Natural enemies were identified to the family level, and these data were examined to determine family richness, diversity, and relative abundance. Compared to unnetted rows, rows covered with hail netting had a significant reduction in both family richness and predator abundance, as measured by yellow sticky traps. The overall abundance of the three most common predator families, Anthocoridae, Empididae, and Coccinellidae, along with other families, was significantly reduced under netting. By contrast, using Simpson's diversity index we found that family diversity was significantly higher under netting, while the insecticides used did not affect diversity. These findings indicate that non-target effects of netting include a general reduction in the abundance of natural enemies and the disproportionate exclusion of Anthocoridae. However, predator diversity was higher under netting, indicating that biological control services could remain intact under netting even with modest use of insecticides.