Effect of conditions in sealed plastic bags on eclosion of mass-reared Queensland fruit fly, Bactrocera tryoni

The sterile insect technique has been used for more than 50 years to control a range of insects around the world. Sterile insect technique is rapidly becoming a major component of many area-wide fruit fly management programmes. Irradiation of immature life stages induces sterility in adults, which are then distributed over large areas to mate with wild flies, resulting in no viable offspring. However, irradiation in normal air results in declining adult quality. To optimize the quality of sterile adult flies, several techniques are available to lower the levels of oxygen in fruit fly tissues prior to irradiation. The simplest method is to seal pupae in plastic bags and allow the oxygen consumption of pupae to minimize oxygen in both the air and pupal tissue. Some fruit fly species have rapid decreases in eclosion as a result of low oxygen atmospheres. We tested the tolerance of Queensland fruit fly, Bactrocera tryoni (Froggatt) (Diptera: Tephritidae), to low oxygen for the first time. In the first two experiments, unirradiated B. tryoni pupae were tested for different periods in sealed plastic bags at 17, 21, and 26°C. Optimum eclosion occurred at 21°C with the lowest eclosion at 26°C. In general, mean full eclosion declined at ca. 0.1% eclosion per hour sealed in plastic bags during the first 96h for all temperatures. In the third and fourth experiments at 17°C, there was a decline in average eclosion for irradiated and unirradiated pupae of about 13.4% after they were sealed in plastic bags for 192h. In general, B. tryoni eclosion declined at 0.1% per hour inside sealed plastic bags for periods up to 192h at 17°C. Queensland fruit flies can tolerate long periods of conditions found inside sealed plastic bags and current practices for sterile B. tryoni release programmes will result in minimum decrease in eclosion. The possible evolution of tolerance of these conditions is discussed.