Cold storage of Queensland fruit fly eggs for mass-rearing programs

Tephritid fruit flies are known worldwide for their destructive impact on agriculture. The Queensland fruit fly, Bactrocera tryoni (or Q-fly), is a highly polyphagous tephritid and is the most economically important insect pest of fruit crops in Australia. With sharp reductions in regulatory tolerance for insecticides, the Sterile Insect Technique (SIT) is currently being developed as a mainstream alternative approach to managing this pest. SIT relies on mass production facilities for massive numbers of high-quality male flies, which are sterilised and released into the field to induce reproductive failure in females of pest populations. Cold storage is a technology whereby mass-produced insects are exposed to sub-optimal temperatures in order to prolong their developmental time. Cold storage would be particularly advantageous for the development of the new SIT programme, but protocols have not yet been developed. Besides reducing costs, having a stockpile of flies ensures readiness for use when seasonal peaks of abundance occur in the field. In the present study, the effect of four temperatures (10, 13, 16 and 19 °C) and three storage periods (3, 6 or 9 days) were evaluated using, as a control, the standard rearing temperature of 25 °C. Biological parameters, including egg hatching rate, larval development, pupal recovery, pupal weight and adult emergence were assessed using a recently developed gel larval diet. The results of this study set the stage for more detailed investigations of the consequences of cold storage on standard quality control parameters used for mass reared fruit flies, such as flight ability and mortality under stress. Future experiments will focus on low-temperature storage of Q-fly pupae, and the consequences of cold storage on the quality of emerging adults.