Selection for age at reproduction changes pre-mating period and mating frequency in Zeugodacus cucurbitae: impacts on insect quality control

In the mass-rearing of insects for sterile insect technique (SIT), it is important to maintain the quality of mass-reared males so that they can compete with wild males in mating with wild females. Mass-reared insects sometimes have shorter pre-mating periods and higher mating frequencies than their wild conspecifics. Indeed, this was the case for mass-reared individuals of the melon fly, Zeugodacus cucurbitae (Coquillett) (Diptera: Tephritidae), used in the SIT program to eradicate the melon fly on the Southwest Islands of Japan. Therefore, I hypothesized that divergent artificial selection for age at reproduction altered these traits in the melon fly as well. To examine the effects of eggs produced by younger parents on each generation, six artificially selected lines were established, for which eggs were collected from young (Y lines) and old (O lines) females. Then, the pre-mating periods and mating frequencies in males and females of the selected lines were compared. The results show a decreased pre-mating period and an increased mating frequency in younger lines compared to older lines, which was driven by males rather than females. These traits ensure efficient offspring production in mass-rearing, and are likely advantageous to the success of SIT programs. The impact of artificially selecting for these traits, especially in males, on insect quality and the efficiency of SIT is discussed.