Operational mark–release–recapture field tests comparing competitiveness of wild and differentially mass-reared codling moths from the Okanagan–Kootenay sterile insect program

Pheromone trap catches and mating activity of sterile, mass-reared, diapaused and non-diapaused male codling moths, Cydia pomonella (L.) (Lepidoptera: Tortricidae), were compared with those of wild diapaused males using mark–release–recapture field experiments in springtime. Sterile moths were provided by the Okanagan–Kootenay Sterile Insect Release (SIR) Program mass-rearing facility, in Osoyoos, British Columbia, Canada. Nondiapause-reared (SIR-standard) and diapause-reared (SIR-diapaused) sterile males were recaptured in similar frequencies. Both types of sterile males were recaptured significantly less often than similarly released wild diapaused males, and ratios of recaptured sterile to wild males were similar with either sterile male. Ratios of sterile to wild males, using the combined catches of SIR-standard and SIR-diapaused males, were significantly lower when measured with traps baited with wild-females (21:1) than with traps baited with 10 μg pheromone (48:1). Both trapping ratios were markedly lower than the 80:1 ratio at which sterile and wild males were released. In mating studies, SIR-standard and SIR-diapaused males exhibited equivalent mating frequencies and both were recaptured in copula with tethered wild females significantly less often than released wild males. In the same mating studies, sterile mass-reared, diapaused males that had been chilled for 3 h at the Pacific Agri-Food Research Centre (PARC) before release (PARC-diapaused) were significantly more competitive than SIR-standard or SIR-diapaused males that averaged 24 h of chilling as part of normal SIR Program operations. PARC-diapaused males and released wild males mated with tethered females with equal frequency. We hypothesize that the length of time SIR males were chilled before being released may have caused SIR-diapaused males to be less mobile, and therefore less competitive with wild males in field mating assays, than were PARC-diapaused males. Based on these results, introduction of a diapause phase into the mass-rearing system used at the Osoyoos facility cannot currently be recommended as a means of improving trap-measured ratios of sterile to wild males, or increasing sterile × wild matings.