Identifying Biologically-Based Paths Reducing Insecticide Resistance in Codling Moth: Progress Report

This progress report describes laboratory and modeling work to develop biologically based strategies for managing insecticide resistance in codling moth, the primary pest of Washington apple and pear production. In 2021, researchers evaluated whether combining codling moth granulovirus with Steinernema nematodes could provide synergistic control when applied to last instar larvae prior to pupation. Laboratory results showed no significant mortality from virus, nematodes, or their combination under these conditions, suggesting trunk applications at this stage are unlikely to improve control.

The team also developed evolutionary models to inform resistance management. Host–parasite models indicate that when pathogen transmission depends on host mortality, incorporating resistant individuals into pathogen rearing may improve biopesticide efficacy. However, epidemiological models suggest that if resistance manifests as reduced pathogen-induced mortality rather than reduced infection, coevolution may not enhance control. These findings highlight that resistance management strategies must account for pathogen transmission mode and resistance type.