Refinement of production and delivery operations to improve quality of sterile Queensland fruit fly, Bactrocera tryoni (Diptera: Tephritidae)
The sterile insect technique (SIT) is currently employed in Australia to manage the Queensland fruit fly Bactrocera tryoni (Froggatt) (Diptera: Tephritidae) (‘Q-fly’), a polyphagous and most damaging pest of horticulture, and is a promising alternative to chemically based control methods. Implementation of the SIT requires a cost-effective system for production and delivery of high quality sterile male insects that can compete with wild male for matings. However, mass produced sterile insects, including Q-fly, often display poor quality arising from ‘industrial’ processes of production, irradiation, post-production handling, transportation, and release. Quality control (QC) tests such as egg hatch, development time, emergence, longevity, and flight ability are conducted routinely to monitor product quality and to identify potential failings. This thesis seeks to improve production and delivery of sterile Q-fly, assessing QC parameters in relation to variation in key processes. I evaluated the effect of domestication on QC parameters, comparing old and young colonies from Brisbane, Cairns and Sydney. Hatching percentage, developmental period, egg to pupae recovery percentage have been decreased and fecundity has been increased by domestication. I then considered pupal size as a quality control parameter, comparting production on gel, carrot and lucerne chaff diets, and the effects of egg seeding densities. Productivity of Q-fly fed on gel diet was higher, and quality was either as good or better than that of carrot and lucerne chaff diets. Emergence rate was higher in gel diet. Small pupae had lower emergence and flight ability rate than larger pupae. Lower egg seeding densities resulted in larger pupae. There was a positive link between pupal diameter, wing length and pupal weight. Significant effects of pupal size were found on adult emergence wing length and male percentage. Next, I investigated the effect of prolonged hypoxia (with no renewal of oxygen, pupae sealed in bags deplete the oxygen levels of the air through their metabolic activity) of irradiated pupae under standard (25°C) and reduced temperature (18°C). Flight ability was acceptable when pupae were stored for up to 2 d at either temperature but was drastically reduced from 4 d. Longevity was reduced after 2 d of hypoxia irrespective of the temperatures. Chilling (sterile insects are exposed to cold temperatures) is used to reduce metabolism of transported adults and I considered the effects of temperature and exposure period on chill coma recovery time, flight ability, survival under nutritional stress and longevity of both males and females. Flies chilled at 4°C took longer to recover than those chilled at 6°C. Flight ability, survival under nutritional stress, and longevity all decreased as chilling period increased but did not differ between the two tested temperatures. I propose (1) Q-fly used for mass rearing should be chosen based on key performance measures, (2) pupal size be included as a routine QC metric for Q-fly, (3) hypoxia of pupae should be kept below 2 d when possible, (4) adult chilling should be kept as short as practicable to maintain fly quality.