Adult dietary experience influences mortality of the pest melon fly, Zeugodacus cucurbitae (Diptera: Tephritidae), to an ingested toxin

Ingested toxins formulated as baits can be effective in the management of insect pests, but their efficacy may be influenced by insect foraging alongside active ingredients. There are several components that might influence insect consumption of toxic baits, one of which being prior nutritional exposure. In our study, we investigated how protein deprivation following adult emergence influences lethal and sublethal effects of boric acid on the pest tephritid melon fly, Zeugodacus cucurbitae. We performed a series of experiments to address the impact of prior diet on mortality, diet consumption, enzymes involved in detoxification and antioxidation and fly activity. Newly emerged melon fly adults were provided either diet containing 3:1 sucrose/yeast hyrdrolysate or just sucrose for three days prior to bioassays. Overall, protein deprivation had a strong effect on fly interactions with boric acid. In two separate experiments (continuous exposure and short duration feeding), insects only pre-fed sucrose had significantly higher mortality compared with those pre-fed protein. Insects that were pre-fed only sucrose removed more liquid diet over the same duration of the experiments, suggesting compensatory foraging behaviours. Adults pre-fed sucrose had higher catalase (1.5×) and superoxide dismutase (1.7×) activities compared with adults pre-fed sucrose-yeast, but we found no effect of boric acid on their activity or that of glutathione-S-transferase or acetylcholinesterase activity. Boric acid consumption also significantly reduced the activity of melon flies. Overall, our results demonstrate that prior diet in fly adulthood can impact subsequent exposure to and efficacy of ingested toxicants.