First Evidence of CpGV Resistance of Codling Moth in the USA

SIMPLE SUMMARY: Different isolates of Cydia pomonella granulovirus (CpGV) have been formulated into different biological control agents that are applied to reduce the infestation and losses induced by codling moth in organic and integrated apple and pear orchards. Cyd-X(®) is the most widely applied CpGV product in apple orchards in the USA and contains a single active ingredient, the isolate CpGV-M (GV-0001). Aiming to investigate the susceptibility of codling moth to GV-0001, we used a discriminating virus concentration to screen five codling moth populations derived from Washington State (USA), which were reared in the laboratory (colony WA1-WA5). The results indicate that colony WA3 had a significantly reduced susceptibility to GV-0001 and survivors from the bioassay can produce offspring. WA3 represents the first documented case of CpGV resistance in the USA. In further tests, WA3 showed resistance to all commercial CpGV agents currently registered in the USA. Nonetheless, the resistant WA3 colony showed high susceptibility to three newly developed CpGV preparations. Therefore, the introduction of the novel CpGV formulations may allow the maintenance of sustainable management programs for codling moth in the USA. ABSTRACT: Codling moth (Cydia pomonella L.) is a very important pest in apple, pear, and walnut orchards worldwide, including the USA. Cydia pomonella granulovirus (CpGV) is used to control codling moth in organic and conventional production. Due to increasing codling moth infestations from organic apple orchards in Washington State, USA, five codling moth colonies (WA1-WA5) were screened for their susceptibility relative to the isolate GV-0001, the main active ingredient of Cyd-X(®), using a discriminating concentration of 6 × 10(4) OB/mL. Compared to a susceptible laboratory colony, the observed results indicated that GV-0001 lacked efficacy against codling moth colony WA3. It was confirmed that WA3 was the first case of codling moth resistance to CpGV in the USA. Further testing of WA3 was performed on a range of CpGV isolates and a lack of efficacy was observed against additional isolates. However, three newly developed CpGV preparations can efficiently infect larvae from the resistant colony WA3. Our results suggest that there is an urgent need to monitor the situation in the USA, aiming to prevent the emergence or spread of additional codling moth populations with CpGV resistance. Strategies to sustain the efficacy of codling moth control using novel CpGV formulations need to be developed.