Ridge gourd volatiles are attractive to gravid female melon fly, Zeugodacus cucurbitae (Coquillett) (Diptera: Tephritidae)

The melon fruit fly, Zeugodacus cucurbitae (Coquillett) (Diptera: Tephritidae), is an important pest of cucurbits throughout India, South-East Asia and Pacific islands. Attractants of female melon fly are of relevance as they could enhance the efficacy of current pest management practices. Previous studies have revealed several host fruits to be attractive to gravid female melon flies. However, studies on the chemical compounds responsible for their attraction are meagre. As an initial part of our study, we evaluated the response of gravid female melon flies to headspace volatiles of four different cucurbit fruits, namely bitter gourd, cucumber, ridge gourd and snake gourd. Electrophysiological and multiple-choice olfactometer assays revealed that gravid melon flies significantly preferred ridge gourd volatiles over volatiles of other cucurbit fruits. Coupled gas chromatography-electroantennogram detection (GC-EAG) analysis of headspace volatiles of ridge gourd to gravid melon flies identified six EAG-active compounds, namely alpha-pinene, 1-octen-3-ol, p-cymene, p-ethyl-benzaldehyde, methyl salicylate and p-cymen-7-ol. Individual EAG-active compounds, except alpha-pinene, were significantly attractive to gravid female flies. Moreover, a synthetic blend with the concentration and ratio of compounds as in the ridge gourd headspace samples was attractive to flies. Though, in a dual-choice test, the preference of gravid melon flies to a synthetic blend was not significantly different from preference to ridge gourd volatile samples. Taken together, our results show that the synthetic blend of ridge gourd volatiles may be used to develop a potential lure for female melon fly, Z. cucurbitae.