Functional Analysis of MsepOR13 in the Oriental Armyworm Mythimna separata (Walker)

Response of Odorant Receptors with Phenylacetaldehyde and the Effects on the Behavior of the Rice Water Weevil (Lissorhoptrus oryzophilus)

The rice water weevil (RWW), Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), is a destructive rice pest that threatens the rice industry worldwide. Odorant receptors (ORs) and odorant receptor coreceptors (Orcos) play an important role in the process of insects' whole life activities; however, there are no related functional studies on RWW. On this basis, a heterologous study of LoryOR20/LoryOrco in Xenopus laevis oocytes was performed to detect the effects of certain natural compounds on RWWs and four active compounds were found. Electroantennogram (EAG) recordings and a behavior test showed that RWWs exhibited a significant response to phenylacetaldehyde (PAA) and an EAG measurement of dsRNA-LoryOR20-treated RWWs revealed a significant decrease in response to PAA. Our results revealed an olfactory molecular mechanism for the recognition of PAA by RWWs, thus providing a potential genetic target at the peripheral olfactory sensing level, contributing to the development of novel control strategies for pest management.

Identification of Odorant-Binding and Chemosensory Protein Genes in Mythimna separata Adult Brains Using Transcriptome Analyses

Large numbers of chemosensory genes have been identified in the peripheral sensory organs of the pest Mythimna separata (Walker) to increase our understanding of chemoreception-related molecular mechanisms and to identify molecular targets for pest control. Chemosensory-related genes are expressed in various tissues, including non-sensory organs, and they play diverse roles. To better understand the functions of chemosensory-related genes in non-sensory organs, transcriptomic analyses of M. separata brains were performed. In total, 29 odorant-binding proteins (OBPs) and 16 chemosensory proteins (CSPs) putative genes were identified in the transcriptomic data set. The further examination of sex- and tissue-specific expression using RT-PCR suggested that eight OBPs (OBP5, -7, -11, -13, -16, -18, -21, and -24) and eight CSPs (CSP2–4, -8, CSP10–12, and -15) genes were expressed in the brain. Furthermore, bands representing most OBPs and CSPs could be detected in antennae, except for a few that underwent sex-biased expression in abdomens, legs, or wings. An RT-qPCR analysis of the expression profiles of six OBPs (OBP3–5, -9, -10, and -16) and two CSPs (CSP3 and CSP4) in different tissues and sexes indicated that OBP16 was highly expressed in male brain, and CSP3 and CSP4 were female-biased and highly expressed in brain. The expression levels of OBP5 and OBP10 in brain were not significantly different between the sexes. The findings expand our current understanding of the expression patterns of OBPs and CSPs in M. separata sensory and non-sensory tissues. These results provide valuable reference data for exploring novel functions of OBPs and CSPs in M. separata and may help in developing effective biological control strategies for managing this pest by exploring novel molecular targets.

Identification of the differences in olfactory system between male and female oriental tobacco budworm Helicoverpa assulta

The olfactory system of insects facilitates their search for host and mates, hence it plays an essential role for insect survival and reproduction. Insects recognize odor substances through olfactory neurons and olfactory genes. Previous studies showed that there are significant sex-specific differences in how insects identify odorant substances, especially sex pheromones. However, whether the sex-specific recognition of odorant substances is caused by differences in the expression of olfaction-related genes between males and females remains unclear. To clarify this problem, the whole transcriptome sequence of the adult Helicoverpa assulta, an important agricultural pest of tobacco and other Solanaceae plants, was obtained using Pacbio sequencing. RNA-seq analysis showed that there were 27 odorant binding proteins (OBPs), 24 chemosensory proteins, 4 pheromone-binding proteins (PBPs), 68 odorant receptors and 2 sensory neuron membrane proteins (SNMPs) genes, that were expressed in the antennae of male and female H. assulta. Females had significantly higher expression of General odorant-binding protein 1-like, OBP, OBP3, PBP3 and SNMP1 than males, while males had significantly higher expression of GOBP1, OBP7, OBP13, PBP2 and SNMP2. These results improve our understanding of mate search and host differentiation in H. assulta.

The general odorant receptor GmolOR9 from Grapholita molesta (Lepidoptera: Tortricidae) is mainly tuned to eight host-plant volatiles

Grapholita molesta is one of the most destructive fruit pests distributed worldwide. Odorant receptors (ORs) located on the dendritic membrane of chemosensory neurons are deemed to be key molecules for sensing exogenous chemical signals. In this study, GmolOR9, a general OR from G. molesta, was functionally characterized. Quantitative real-time polymerase chain reaction revealed that GmolOR9 was more highly expressed in adults than in other stages, including eggs, larvae, and pupae. GmolOR9 expression was highly significantly more in the antennae of females than in those of males, and the highest level occurred in the antennae of 3-day-old female adults. GmolOR9 was broadly tuned to eight of 47 odorant components tested, including (Z)-3-hexenyl acetate, butyl propionate, ethyl hexanoate, ethyl heptanoate, 1-hexanol, (Z)-3-hexenol, 2-ethyl-1-hexanol, and linalool, by in vitro heterologous expression. Furthermore, electroantennogram responses indicated that the effects of dsOR9-injected females to (Z)-3-hexenyl acetate dramatically decreased. These results suggested that GmolOR9 might be involved in detecting host-plant volatiles. Moreover, (Z)-3-hexenyl acetate might serve as a potential attractant for the biological control of G. molesta.

Cloning and Functional Characterization of Three Odorant Receptors From the Chinese Citrus fly Bactrocera minax (Diptera: Tephritidae)

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.

Detecting Host-Plant Volatiles with Odorant Receptors from Grapholita molesta (Busck) (Lepidoptera: Tortricidae)

Grapholita molesta is a global pest of stone and pome fruits. The sensitive olfactory system plays a crucial role in regulating key behavioral activities of insects and G. molesta relies heavily on general odorant receptors (ORs) to detect host-plant volatiles. In this study, three general OR genes from G. molesta (GmolOR12, GmolOR20, and GmolOR21) were identified. Quantitative polymerase chain reaction revealed that GmolORs expression was considerably higher in adults and adult antennae than in any other life stages and body parts, respectively. Moreover, the expression of GmolORs was significantly higher in the antennae of females than in those of males, with a peak in the antennae of 3-days-old adult females. GmolOR20 and GmolOR21 displayed no responses to any of the odorant compounds tested in the Xenopus oocyte system. GmolOR12 was tuned mainly to 5 of the 47 odorant components tested (including decanol, heptanal, octanal, nonanal, and decanal), and the response to aldehydes among the 5 components was the highest. Additionally, they all elicited female and male antennae electroantennogram responses, and the aldehydes elicited the highest response among the 5 components. These results suggested that GmolOR12 in the G. molesta olfactory system plays an important role in sensing aldehydes and that GmolOR12 is involved in sensing host-plant volatiles. These findings provide insight into the possibility of using host-plant volatiles for the control of G. molesta.