Insect olfactory sensing is crucial for finding food, mating, and oviposition preference. Odorant receptors (ORs) play a central role in the transmission of odorant signals into the environment by the peripheral olfactory system. Therefore, the identification and functional study of ORs are essential to better understand olfactory mechanisms in insects. OR studies on Diptera insects are primarily performed on Drosophila and mosquitoes, but few studies have been reported in Tephritidae. In this study, we examined three candidate ORs (BminOR3, BminOR12, and BminOR16) from Bactrocera minax. Our analysis of tissue expression revealed that the three BminORs were expressed in the antennae, with no difference between the male and female. In in vitro heterologous expression system of Xenopus oocytes. BminOR3/BminOrco responded strongly to 1-octen-3-ol, BminOR12/BminOrco responded to eight compounds [methyl salicylate, benzaldehyde, (Z)-3-hexenyl acetate, butyl acrylate, butyl propionate, 1-octanol, (S)-(+)-carvone and benzyl alcohol], and BminOR16/BminOrco slightly responded to undecanol. Our results concluded that BminOR3, BimOR12, and BminOR16 could play an important role in host-finding and oviposition positioning in B. minax.

Plants have evolved various self-defense mechanisms against insect feeding. There are many reports regarding both direct and indirect defense mechanisms in seed-plant. However, only direct defenses on ferns were considered and the indirect defense mechanism has never been reported. In this study, it was observed that the fern Hypolepis punctata can attract the assassin bug Sclomina erinacea in the field. We collected and analyzed volatiles from H. punctata healthy individuals and the ones wounded by Bertula hadenalis, using dynamic headspace and GC-MS. We recorded the electroantennogram responses of antennae of S. erinacea to different standards of volatile compounds identified from the GC-MS analysis. We also analyzed the behavior of male and female S. erinacea adults in response to volatiles collected from H. punctata using a Y-tube olfactometer. The results showed that a number of volatile compounds were produced when the fern was damaged by B. hadenalis. Electroantennography and Y-tube olfactometer results showed that some herbivore-induced volatiles and volatiles from undamaged leaves could attract S. erinacea. Our research suggests that H. punctata can attract insect predators by releasing herbivory-induced volatile organic compounds, and for the first time we found ferns may also have indirect defense mechanisms using volatile organic compounds.