The effect of larval diets on pupal size distribution and quality parameters of the Queensland fruit fly (Diptera: Tephritidae)

Queensland fruit fly (Q-fly) presents serious threats in Australian horticulture industry. The sterile insect technique (SIT), which involves mass production and release of millions of sterile insects, is employed to manage Q-fly in Australia. For SIT to succeed, the mass-produced flies need to be of high quality and this is assessed through a standardised set of quality control parameters. Pupal size is one of the most important quality control metrics, and can be assessed as pupal diameter. Compared with batch weighing, a common alternative, sorting pupae individually by diameter provides better information on pupal size distribution and variance. We assessed the size distribution of pupae that had been reared on gel, carrot and lucerne chaff-based larval diets. A pupal size sorter was used to separate the pupae into 13 diameter categories which were then pooled into five general categories (very small, small, medium, large, and very large) for quality control analysis. Gel diet produced more pupae and produced pupae homogenous in size that were of quality as good as or better than those from carrot and lucerne chaff diets. Wing length of adult flies was positively associated with pupal size. Across larval diets, very small pupae had low adult emergence rate and flight ability, and the larger pupal sizes had a heavily female-biased sex ratio.