Age-dependent response of female melon fly,Zeugodacus cucurbitae (Diptera: Tephritidae), to volatiles emitted from damaged host fruits

In many insect species including fruit flies (Diptera: Tephritidae), the behavioral responses to volatiles emitted by their host plants can be modulated by environmental conditions and by the physiological state of the insect. Here, we quantified (1) the effects of female age on the attraction of female melon fly, Zeugodacus cucurbitae (Diptera: Tephritidae) to volatiles emitted by intact and mechanically damaged tomato (Solanum lycopersicum), eggplant (S. melongena), zucchini (Cucurbita pepo), bitter melon (Momordica charantia), and cucumber (Cucumis sativus) fruit, and (2) the influence of time elapsed since fruit damage on the outcome. The investigations were conducted under semi-natural conditions in Hawai’i. Results from the first experiment revealed that, for freshly damaged tomato, eggplant, and zucchini, the level of female response was comparatively low and was not affected by female age. For bitter melon and cucumber, higher levels of response to freshly damaged fruit were documented, and the response levels gradually increased as female age increased from 1 to 4 weeks, reaching 70% for 4-week-old females exposed to cucumber odor. Results from our second experiment indicated that, on average, 56% of the females released responded in 20 min when cucumbers were freshly sliced, and the level of response was reduced 6-fold within a couple of hours. Females did not respond to tomato and cucumber odor when fruits were damaged >8 h before testing. Fruit volatiles involved in female Z. cucurbitae attraction seem to be released shortly upon mechanical damage and they are short-lived. The plasticity of the olfaction-driven behavior observed in Z. cucurbitae depending on female age and on the strength of the olfactory cues associated with preferred and less preferred hosts, adds another dimension to our understanding of the host-seeking behavior of this invasive species.