Harlequin ladybird (Harmonia axyridis (Pallas, 1773)) is an invasive species originating from Asia, posing a potential threat to the ecosystem and the wine industry in New Zealand due to wine taint, although it can also be a useful biocontrol agent. In this study, the response profiles of antennal olfactory receptor neurons (ORNs) to 32 plant volatiles were examined in male and female H. axyridis, using the single sensillum recording technique. Various types of ORNs were identified from four types of olfactory sensilla in both male and female H. axyridis, with no sexual dimorphism. The most abundant type of sensilla contained two ORNs exhibiting highly specialized responses to methyl benzoate and β-caryophyllene, respectively. Another type of sensilla also contained two specialized ORNs, one responsive to geranyl acetate and the other to some aromatic compounds such as 2-phenylethanol, benzyl acetate, methyl benzoate, and methyl phenylacetate. In contrast, two other types of sensilla contained broadly tuned ORNs, one containing ORN(s) responsive to six-carbon alcohols such as (Z)-3-hexen-1-ol, 1-hexanol, and isomers of 2-hexen-1-ol as well as some other non-alcohol green leaf volatiles, and the other containing ORN(s) exhibiting responses to β-myrcene, geraniol, linalool, nerol, benzyl acetate, and methyl phenylacetate. This study suggests that H. axyridis possesses a set of ORNs specialized for specific plant volatiles, providing insights into the olfactory communication system of this species and potential volatiles to be used for trapping this insect.

Olfactory receptors (OR) are primarily responsible for the detection of odorant molecules. We previously demonstrated that OR7D4, an OR for androstenone, is expressed in the vomeronasal organ and olfactory epithelium tissue of stallions. Recently, the expression of OR1I1 in the human testes was reported and the possible roles of OR1I1 in the testicular cells were suggested. The objectives of this study were 1) to explore the expression of OR7D4 and OR1I1 in stallion testes, and 2) to define the specific localization of OR7D4 and OR1I1 in the testicular tissues. Stallion testicular tissue samples were used for this study. Western blot was performed to confirm the cross-reactivity of OR7D4 and OR1I1 antibody with stallion testicular tissue samples. OR7D4 and OR1I1 gene expressions were investigated using reverse transcriptionpolymerase chain reaction (RT-PCR) in stallion testes. Immunofluorescence was performed to investigate the expression of OR7D4 and OR1I1 in stallion testicular tissues. The protein bands for OR7D4 and OR1I1 from the testes were observed at approximately 38 kDa and 43 kDa, respectively. The mRNA of OR7D4 and OR1I1 were detected in stallion testes. Immunolabeling of OR7D4 and OR1I1 in the cytoplasm of both spermatogonia and Leydig cells was observed. In conclusion, androstenone and another odorant chemical, which is recognized by OR1I1, may play an important role in stallion testes.

Electrophysiological responses of Queensland fruit fly, Bacterocera tryoni, were investigated to identify the olfactory receptor neurons (ORN) in the antennae and corresponding active volatile compounds, using the single sensillum recording technique and 52 test compounds including methyl methyl eugenol, cuelure and raspberry ketone. We found that different classes of olfactory sensilla and ORNs are present in the antennae of B. tryoni. Most of the ORNs appeared to have narrow response spectra, exhibiting specialized responses to one or a few volatile compounds among the 52 compounds tested. In this study, ORNs specialized for ammonia, nonanal, isopentanol, ethyl acetate, indole, phenol, 2,5-dimethylpyrazine and 2-coumaranone, respectively, have been identified. A class of ORNs exhibited highly specialized responses to methyl eugenol. A preliminary field trapping test conducted in New Caledonia to evaluate the behavioral activities of the olfactory active compounds indicated a blend of three synthetic compounds is attractive to female B. tryoni.

Antennal olfactory receptor neurons (ORNs) for pheromone and plant volatile compounds were identified and characterized in Sitona lepidus and S. discoideus, using the single sensillum recording technique with five pheromone-related compounds and 40 host and non-host plant volatile compounds. Different types of olfactory sensilla containing specialized ORNs were identified in these weevils. Different types of sensilla housed ORNs specialized for pheromone-related compounds, 4-methyl-3,5-heptanedione or one or more of four stereoisomers of 5-hydroxy-4-methyl-3-heptanone. In addition to the pheromone-related ORNs, several types of olfactory sensilla contained ORNs responsive to plant volatile compounds. Most of the ORNs showed high specificity to specific volatile compounds although some of the active compounds showed overlapping response spectra in the ORNs across different types of sensilla. Our study indicates that both S. lepidus and S. discoideus have species-specific set of highly sensitive and selective ORNs for pheromone and plant volatile compounds. The behavioral implication of these findings is discussed.

Phytophagous insects detect volatile compounds produced by host and non-host plants, using species-specific sets of olfactory receptor neurons (ORNs). To investigate the relationship between the range of host plants and the profile of ORNs, single cell recordings were carried out to identify ORNs and corresponding active compounds in female Uraba lugens (Lepidoptera: Nolidae), an oligophagous eucalypt feeder. Based on the response profiles to 39 plant volatile compounds, 13 classes of sensilla containing 40 classes of ORNs were identified in female U. lugens. More than 95% (163 out of 171) of these sensilla contained 16 classes of ORNs with narrow response spectra, and 62.6% (107 out of 171) 18 classes of ORNs with broad response spectra. Among the specialized ORNs, seven classes of ORNs exhibited high specificity to 1,8-cineole, (±)-citronellal, myrcene, (±)-linalool and (E)-β-caryophyllene, major volatiles produced by eucalypts, while nine other classes of ORNs showed highly specialized responses to green leaf volatiles, germacrene D, (E)-β)-farnesene and geranyl acetate that are not produced by most eucalypts. We hypothesize that female U. lugens can recognize their host plants by detecting key host volatile compounds, using a set of ORNs tuned to host volatiles, and discriminate them from non-host plants using another set of ORNs specialized for non-host volatiles. The ORNs with broad response spectra may enhance the discrimination between host and non-host plants by adding moderately selective sensitivity. Based on our finding, it is suggested that phytophagous insects use the combinational input from both host-specific and non-host specific ORNs for locating their host plants, and the electrophysiological characterization of ORN profiles can be used for predicting the range of host plants in phytophagous insects.

Insects and animals can recognize surrounding environments by detecting thousands of chemical odorants. Olfaction is a complicated process that begins in the olfactory epithelium with the specific binding of volatile odorant molecules to dedicated olfactory receptors (ORs). OR proteins are encoded by the largest gene superfamily in the mammalian genome. We report here the whole genome analysis of the olfactory receptor genes of S. scrofa using conserved OR gene specific motifs and known OR protein sequences from diverse species. We identified 1,301 OR related sequences from the S. scrofa genome including 1,113 functional OR genes and 188 pseudogenes. OR genes were located in 46 different regions on 16 pig chromosomes. We classified the ORs into 17 families, three Class I and 14 Class II families, and further grouped them into 349 subfamilies. We also identified inter- and intra-chromosomal duplications of OR genes residing on 11 chromosomes. A significant number of pig OR genes (n=212) showed less than 60% amino acid sequence similarity to known OR genes of other species. We also performed a similar analysis on the cattle OR subgenome and identified 1,071 OR related sequences. We show that S. scrofa has one of the largest OR repertoires, suggesting an expansion of OR genes in the swine genome. Considering available information from literature, it seems that OR systems between mammals and insects possess high similarity in their action mechanisms and rapid evolutionary changes due to differences in living environments.