Effects of pupal hypoxia duration and holding temperature on quality control parameters of sterile Queensland fruit fly

Background: The sterile insect technique is used to eradicate outbreaks of Queensland fruit fly (Q-fly) Bactrocera tryoni (Froggatt) in fruit-fly-free regions of Australia and shows promise for suppression in endemic areas. Prior to irradiation, pupae are sealed in plastic bags to induce hypoxia, reducing oxidative stress and delaying adult emergence. After irradiation, pupae are transported to rear-out centers under continued hypoxia. Previous studies reported only modest reductions in adult emergence following hypoxia. Here, we assessed the effects of hypoxia duration and temperature on multiple quality parameters. Pupae were stored under hypoxia for 0, 1, 2, 4, 6, and 8 days at 18 and 25 °C. In addition to standard quality control parameters (emergence rate, longevity and flight ability), a locomotor activity monitor was used to assess pre-emergence period, survival, and locomotor activity under nutritional stress. 

Results: Pre-emergence period and survival under nutritional stress was not affected by hypoxia duration or temperature. However, number of fly movements per hour under nutritional stress were reduced after 4 days of hypoxia. Adult emergence and flight ability were unaffected up to 2 days of hypoxia but declined sharply after 4 days or longer, with stronger effects at 25 °C. The percentage of partial emergence and deformed adults also increased significantly after 4 days. 

Conclusion: Q-fly pupae can safely endure hypoxia for up to 2 days, with storage at 18 °C recommended for longer durations to minimize impacts on emergence and flight ability.