ENTOMOPATHOGENS FOR CODLING MOTH CONTROL: THEORY AND DATA

Jeremy Peter Roberts

doi:10.7273/000004539

The evolution of insecticide resistance in pest species is a major concern in many agricultural systems. Rotation of control measures is typically used to slow the spread of resistance. Modern molecular techniques have improved our ability to identify pathogens to be used as biopesticides, providing good control methods to rotate with traditional insecticides, given the typically different modes of action. Furthermore, entomopathogens can be applied similarly to traditional insecticides from similar equipment. Granulovirus is widely used as a biopesticide to control codling moths, the key apple pest, but there are widespread resistance concerns. Entomopathogenic nematodes are also used on codling moths with mixed success. The virus and nematodes target codling moth larvae and pupae, respectively, and I hypothesized that virus exposure in the host would improve nematode attack success, by weakening immune function. I evaluated a novel application of the virus to last instar larvae, and emulated an application of nematodes to tree bark (in the absence of soil), which is suggested on product labels, but with limited research. I observed little impacts of either pathogen on codling moth survival. Therefore, the direct spray method of nematode application to tree trunks at current rates is likely not effective for control. In addition to my experimental evaluation of biopesticides, I used mathematical models to develop theory for biopesticide resistance mitigation programs, where the pathogens evolving alongside pests may offer improved control of resistant pests. Here, I considered two scenarios of biopesticide evolution: one where a parasite must kill the host for transmission to occur, and an epidemiological scenario where pathogen transmission between living hosts and virulence are each governed by host and pathogen traits. In the resource-consumer case, biopesticide evolution can improve control. However, in the epidemiological case, the type of host mutation (tolerant/reduced virulence vs resistant/reduced transmission) affects whether biopesticide evolution can improve control. Resistant hosts decrease pathogen population, so pathogen evolution should combat resistance, but tolerant hosts increase pathogen population without pathogen selection pressure to increase virulence. I discuss the application of this theory for developing biopesticide resistance management programs to improve the sustainability of agricultural practices.

ENTOMOPATHOGENS FOR CODLING MOTH CONTROL: THEORY AND DATA

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