Volatile chemical signals released by host plants are important for melon flies to find suitable hosts, feed, and oviposit. Melon flies prefer cucurbits as host plants, and their attraction to several fruits, including cucumbers, bitter gourds, snake gourds, and zucchini, has been documented (Subhashet al., 2018; Piñero et al., 2019). However, only cucumber volatiles have been studied as attractants of female B. cucurbitae (Siderhurst and Jang 2010). Therefore, the search for attractants from other hosts is important.
Thus far, compounds emitted by ridge gourd have been studied fragmentedly, six and EAG-active compounds were identified as α-pinene, 1-octen-3-ol, pcymene, p-ethyl-benzaldehyde, methyl salicylate and p-cymen-7-ol (Shivaramu et al., 2022). In the current study, twelve types of EAG-active compounds were identified, including α-pinene. The low similarity with our results could be due to both methodological differences and a significant difference in temperature systems used for the collection of compounds, ridge gourd varieties, absorbents, and plant tissue sites (Murungi et al., 2018; Yang et al., 2019).
However, previous studies on insect olfaction have revealed that only a minority of the components in complex odor blends can be detected by insect antennae (Jonsson et al.,1999; Baur et al.,1993; Rojas, 1999). Among the EAG-active compounds, a few appear to be involved in mediating insect behavioral responses (Fraseret al., 2003; Būda et al., 2022). In general, the strength of the EAG response increases with the concentration tested over a range of doses, which is determined by the innate properties of olfactory neurons (Yves et al., 1995; Hoffmann et al., 2020). The differing behavioral effects of different concentrations of compounds are associated with their inherent chemical nature (Liu et al., 2022). The EAG response of the insects only indicated the sensitivity of B. cucurbitae to volatile substances, and the specific function of the volatile substances was determined through behavioral experiments.
Volatile components at different concentrations may have different ecological functions, and the same substance may exhibit attractive or repellent effects at different concentrations (Moreno et al.,2022; Cao et al.,2022; Song et al.,2021). In the present study, methyl isovalerate, methyl myristate, methyl laurate, and 1-octadecene were found to have both attractive and repellent effects on B. cucurbitae. The effect of methyl isovalerate on both sexes changed from attractive to repellent. According to previous reports, methyl isovalerate in Fusarium solani attracts Xylosandrus compactus (Egonyu et al., 2018), and repels flies (Henderson et al., 1991). In addition, 1-octadecene is a repellent component of Spodoptera frugiperda (Kong et al., 2023) and an attractive component of M. incognita (Ding et al., 2023). Previous studies have shown that methyl myristate is attractive to Varroa destructor (Liu et al., 2022), Drosophila melanogaster, (Keesey et al., 2017; Dweck et al., 2015), and Drosophila suzukii (Matsumura) (Tait et al., 2020) but repellent to Psoroptes ovis (Hering) (Dunn et al., 2019). Further, methyl laurate has been previously reported as a pheromone in D. melanogaster (Keesey et al., 2017; Dweck et al., 2015) that repels Amblyomma sculptum (Barrozo et al., 2021) and Aedes aegypti (Zhang et al., 2020). In addition, heptanal can be used as an attractant for Rhipicephalus sanguineus (López-López et al., 2023), a sex pheromone of Plodia interpunctella (Liu et al., 2021), and as a repellent for Cotesia glomerata (L.) (Xu et al., 2020). Lastly, 1-decanol is a repellent for fire ants. The combination of volatiles, as opposed to a single active substance, may be the reason for the differing results in behavioral responses (Stübner et al.,2023; Baig et al., 2023). Thus, methyl isovalerate, methyl myristate, 1-octadecene, methyl laurate, heptanal, and 1-decanol could be mixed in certain proportions for further experiments, laying the foundation for the selection of attractants and repellents.
In this study, we found that several volatile compounds could be used as behavioral regulators in melon flies. Field experiments were conducted on volatile mixtures to develop a synthetic bait for melon flies, which laid the foundation for monitoring and effectively controlling B. cucurbitae in an environmentally friendly manner.