Developing Field Cage Tests to Measure Mating Competitiveness of Sterile Light Brown Apple Moths (Lepidoptera: Tortricidae) in Western Australia

The Australian light brown apple moth (LBAM) (Epiphyas postvittana) (Walker) (Lepidoptera: Tortricidae) is a pest in Australia, New Zealand and now California (USA). The use of sterile insects in combination with mating disruption and biological insecticides has the potential to eradicate outbreaks in urban areas. The sexual competitiveness of irradiated insects is an important component of the effectiveness of the sterile insect technique (SIT), but standard techniques to measure the sexual competitiveness have been developed only for irradiated tephritid fruit flies. In particular, field cage trials have been used to measure the compatibility and competitiveness of irradiated fruit flies in comparison with wild fruit flies. Trials were carried out to determine if such tests could be adapted for a moth species. Parameters of quality or competitiveness evaluated were the proportion of the moths that mated, relative sterility index, index of sexual isolation, and mating competitiveness based on the egg hatch in the various crosses. Results showed that with the release of sterile moths of both sexes (bisex) there was little difference in competitiveness—expressed as the Relative Sterility Index (RSI)—between moths irradiated at 200, 250 and 300 Gy (irradiated either in the pupal or adult stages), but if a Fried competitiveness test was used to generate competitive C values then greater competitiveness was found at the lower doses of irradiation, but this difference was not statistically significant. Modified test procedures were developed in which the moths in field cages—after having had sufficient opportunity to mate—were egged individually and dissected to determine the presence of 1 or more spermatophores; then egg sterility and spermatophore presence were used to determine the mating type, e.g., wild female × irradiated laboratory male, etc. Results indicated that sterile-male-only releases have the potential to increase mating competitiveness of the released irradiated moths, but this conclusion requires additional experiments for confirmation.