Abstract: The present study is an important step toward calibrating, validating and improving irradiation methods used for Queensland fruit fly sterile insect technique (SIT). We used routine IAEA/USDA/FAO quality control tests assessing percentage emergence, flight ability, sex ratio, mortality under stress, longevity under nutritional stress, reproductive sterility and sexual competitiveness, to assess the impact of a range of target irradiation doses (60, 65, 70, 75 and 80 Gy) on the product quality of mass reared Queensland fruit fly used in SIT. Sterility induction remained adequate (> 99.5%) across the full range of irradiation doses tested. However there was significant reduction in survivability and competitiveness of irradiated flies as dose increased. The current target sterilizing dose for SIT of 70-75 Gy is associated with elevated damage to flies. Our data suggest that adequate sterility and improved fly quality could be achieved through a small reduction in target sterilizing dose.
Abstract: The mating performance â¬eld cage test is a required periodic quality-control assessment for factory- reared fruit Âies used for the sterile insect technique. The FAO/IAEA/USDA guidelines for assessing fly quality state that if during tests a large proportion of flies call and mate on cage walls, away from host trees, then environmental conditions within the cage need to be adjusted and tests repeated. Here we test effects of cage design, specifcally mesh colour (green, white) and addition of supplementary shade, on the mating behaviour of Queensland fruit fly (Q-fly), Bactrocera tryoni Froggatt (Diptera: Tephritidae). Observations were made over a 4-h period at dusk when these flies mate. Changes in environmental conditions in each cage over the dusk period varied with cage design. We recorded the highest proportion of matings taking place on trees as opposed to cage walls (> 90%) in the unshaded white cage, the shaded white and un-shaded green cages being intermediate (ca. 70%), and the shaded green cage had the least (ca. 40%). The effects of field cage colour and supplementary shade on mating behaviour are discussed. We recommend that Q-fly field cage tests should be conducted in cages with a light coloured mesh, and that supplementary shading should only be applied if there is a need to adjust temperature and light within the cage.
Abstract: Queensland fruit fly (Bactrocera tryoni; Q-fly) pupae are routinely irradiated to induce reproductive sterility in adults released in a sterile insect technique programme. Although there have been some studies of how total dose influences fly quality, dose rate has not been considered. In the present study, pupae were irradiated at a target dose range of 70â75 Gy at dose rates of approximately 5, 7, 26, 57 and 80 Gy/min and were then subjected to routine IAEA/FAO/USDA quality control tests including emergence, flight ability, mortality under stress and sterility induction. No significant effects of dose rate were found on emergence or flight ability. Sterility induction was also found to be independent of dose rate, a result conforming to a âone-hitâ ionizing event hypothesis. Flies irradiated at higher dose rates suffered increased mortality under stress. This appears to stem from an increased tendency to over-shoot the target dose when irradiating at high dose rates. We recommend that, to reduce potential error in total target dose, the lowest practical dose rate be used when irradiating Q-fly pupae for use in the sterile insect technique.
