Is lack of mating competitiveness in spring linked to mating asynchrony between wild and mass‐reared codling moths from an operational sterile insect programme?

Abstract

Mating competitiveness and pheromone trap catches of mass-reared, male codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), from the Osoyoos, British Columbia, Canada, massrearing facility operated by the Okanagan-Kootenay Sterile Insect Release Board, were compared to wild males using mark-release-recapture field experiments in spring, summer, and autumn at Summerland, British Columbia. In spring, significantly more wild diapause males mated with tethered, wild females than did non-irradiated (0 Gy) or irradiated (100 or 250 Gy) non-diapause, mass-reared males. A lower dose of radiation did not improve mating competitiveness, nor catches of mass-reared males released in spring. Median mating time for wild males was approximately 45 min earlier than mass-reared males with most wild males (70.5%) mating before sunset and mass-reared males mating at or shortly after sunset in spring. Superior mating competitiveness of wild males in spring was mirrored by greater recapture rates in pheromone-baited traps. In summer, mating competitiveness of mass-reared moths improved relative to wild males and there was a significant inverse relationship between radiation dose (0, 100, and 250 Gy) and competitiveness of mass-reared males. In autumn, untreated, wild males were significantly more responsive to pheromone traps than non-diapausing mass-reared males receiving 250 Gy of radiation. Mass-reared males, subjected to diapause-inducing conditions as larvae and emerged from diapause before this irradiation treatment, were recaptured significantly more often than similarly irradiated, non-diapause, mass-reared males, but not more than untreated, diapause wild males. We hypothesize that differences between wild and mass-reared males in daily timing or speed of responses to natural or synthetic pheromone sources under montane weather patterns typical of spring in British Columbia may partially explain poor activity of sterile males, and low sterile : wild overflooding ratios during spring when measured using pheromone traps by the sterile insect release programme in British Columbia.

Modelling the effects of inherited sterility for the application of the sterile insect technique

“…Here, relative competitiveness, c S , was estimated as the mean number of matings observed by irradiated males relative to that for releases of control males. Although a similar experiment also recorded copulations with wild males ( Judd et al , 2006 ), these data could not be used to derive estimates for the competitiveness of irradiated males relative to wild ones because the absolute density of wild moths was unknown. Data from pheromone trap catches could not be used to estimate wild moths relative to the number of irradiated males released because these trap results would have been affected by some of the same competitiveness factors affecting the copulation results.…”

Female mating failure and the failure of ‘mating’ in sterile insect programs

“…However, there was no difference in the time of participation between wild flies from Maui and Kona and sterile flies (Lance et al, 2000). Similarly, sterile codling moth males initiate flight and mate finding approximately 45 min earlier than wild moths, which results in lower mating success (Judd et al, 2006). Similarly, sterile codling moth males initiate flight and mate finding approximately 45 min earlier than wild moths, which results in lower mating success (Judd et al, 2006).…”

“…As mating competitiveness, and presumably female choosiness, can decrease with increasing laboratory generations (Iwahashi et al, 1983), additional studies on male irradition using F1 wild individuals are needed. In a field study of the codling moth, Cydia pomonella (L.), wild females were less likely to mate with mass-reared males, regardless of whether they had been irradiated or not, compared to wild males (Judd et al, 2006). In another study with this same species in a laboratory walkin cage, wild females were more likely to mate with wild males than with mass-reared males irradiated at either 3 or 8 krad.…”

“…Thus, differences in mating success cannot directly be attributed to irradiation or mass-rearing. In a field study of the codling moth, Cydia pomonella (L.), wild females were less likely to mate with mass-reared males, regardless of whether they had been irradiated or not, compared to wild males (Judd et al, 2006).…”

Mating rates between sterile and wild codling moths (Cydia pomonella) in springtime: A simulation study

“…The response of male mass-reared moths to pheromone stimuli in spring may differ significantly from that of wild moths. Sterile male moths appear to initiate flight and matefinding at a different time of day than wild moths and their success in mating is greatly reduced (Judd et al, 2006). This is perhaps caused by a difference in the moths' response to environmental stimuli.…”