Domestication-related changes in sexual performance of Queensland fruit fly

In Sterile Insect Technique (SIT) programs, massive numbers of insects are reared, sterilized, and released in the field to impede reproduction of pest populations. The domestication and rearing processes used to produce insects for SIT programs may have significant evolutionary impacts on life history and reproductive biology. We assessed the effects of domestication on sexual performance of laboratory reared Queensland fruit fly, Bactrocera tryoni, by comparing an old (49 generations) and a young colony (5 generations). We evaluated mating propensity, mating latency, copula duration, sperm transfer, and ability to induce sexual inhibition in mates. Overall, both males and females from the old colony had greater mating propensity than those from the young colony. Copula duration was longer when females were from the old colony. There was no evidence of sexual isolation between the colonies as males and females from the two colonies had similar propensity to mate with flies from either colony. Males from the old colony transferred more sperm regardless of which colony their mate was from. Finally, males from both colonies were similarly able to induce sexual inhibition in their mates and were also similarly able to secure copulations with already-mated females. Positive effects of domestication on sperm transfer, coupled with maintained ability to induce sexual inhibition in mates and to secure copulations with previously mated females, highlights that domestication may have little effect, or even positive effects, on some aspects of sexual performance that may advantage mass-reared B. tryoni in SIT programs.

The effect of captive breeding upon adult thermal preference in the Queensland fruit fly (Bactrocera tryoni)

The Queensland fruit fly (Bactrocera tryoni) is a generalist pest that poses a significant threat to the Australian horticultural industry. This species has become broadly established across latitudes that encompass tropical to temperate climates, and hence populations occupy diverse thermal niches. Successful expansion across this range may have been brokered by evolutionarily labile features of breeding phenology, physiology and/or behaviour. We explored the potential role of behavioural flexibility by characterizing variation in adult thermal preference using a novel gradient apparatus. Flies oriented within this apparatus essentially at random in the absence of thermal variation, but sought and maintained precise positions when presented with an established gradient. Male and female flies from an 'old' colony (>300 generations) and a 'young' (F7) colony were compared. Whereas we found no difference between the sexes, flies from the young colony preferred higher temperatures (30.93 ± 7.30 °C) and had greater individual variation than their counterparts from the old colony (28.16 ± 5.63 °C). Given that B. tryoni are routinely maintained at 25 °C in the laboratory, a lower mean preference of the old colony is consistent with thermal adaptation. This is further supported by their reduced phenotypic variance, which follows as a logical consequence of stabilising selection given long-term environmental constancy. These results demonstrate that B. tryoni seek to thermoregulate via adult behaviour, and that individual temperature preference can be precisely measured using a gradient apparatus. The evidence for adaptive tuning of this behaviour has importance for both the design of captive rearing protocols as well as the prediction of invasive potential and species biogeography under future climatic variation.