The oriental fruit fly, Bactrocera dorsalis (Hendel), is a devastating pest of citrus fruits.  After successful mating, adult females insert their eggs into the ripened fruit, resulting in moldy and rotten fruit and causing great economic losses for the citrus industry.  In the field, flies initiate copulatory behaviors as twilight approaches, and decreasing light intensity in this period is the normal stimulus for copulation.  In this study, ten light intensities ranging from 0–30 000 lux were set to identify the typical intensity that strongly regulates the copulation behavior of B. dorsalis.  Three light intensities found to regulate the copulation behavior were then selected to verify their effects on adult male wing fanning and female chemotaxis towards 2,3,5-trimethylpyrazine (TMP).  At last, strong light and complete darkness were artificially combined in the lab to verify whether they could prevent copulation to inform behavioral manipulation of oriental flies in the future.  The results indicated that adult flies generally initiated copulatory behaviors at low light intensity (<1 000 lux).  
Stronger light significantly prevented copulation in proportion to intensity, with nearly no copulation events initiated when light intensity was above 20 000 lux.  Both male wing fanning and female chemotaxis towards TMP were attenuated as light intensity became stronger.  However, at 10 000 lux, males still fanned their wings to a certain extent while TMP completely lost its attractiveness to females.  In the darkness, adults did not initiate any sexual behaviors, e.g., copulation, wing fanning, or chemotaxis to TMP.  One hour of strong light (10 000 lux) combined with continuous darkness completely prevented mating.  These results show that light condition is an essential factor for copulatory behaviors in the oriental fruit fly.  Researchers could thus manipulate light conditions artificially or disrupt the molecular target in flies’ light transduction pathway to develop environmentally-friendly techniques to control this pest.

Odorant receptor (OR) is crucial for insects to detect and recognize external chemical cues closely related to their survival.  The insect OR forms a heteromeric complex composed of a ligand-specific receptor and a ubiquitously odorant receptor coreceptor (Orco).  This study used the CRISPR/Cas9 technique to knock out (KO) Orco and reveal its essential role in acting on OR-meditated olfactory behavior in a critical invasive agricultural pest, the fall armyworm (FAW), Spodoptera frugiperda.  Electroantennogram (EAG) results suggested that the Orco mutants of both male and female moths severely reduced their electrophysiological responses to the eight tested plant volatiles and two sex pheromones.  However, the Orco gene played distinct roles in mating behavior between sexes: the mating behavior was fully disrupted in mutated males but not in mutated females.  The oviposition result indicated that the Orco KO females displayed reduced egg laying by 24.1% compared with the mated wild type (WT) females.  Overall, these results strongly suggest that Orco is an excellent target for disrupting FAW’s normal behavior and provides a feasible pest control approach.

Herbivore-induced plant volatiles (HIPVs) play a key role in the interactions between plants and herbivorous insects, as HIPVs can promote or deter herbivorous insects’ behavior.  While aphids are common and serious phloem-feeding pests in farmland ecosystems, little is known about how aphids use their sensitive olfactory system to detect HIPVs.  In this study, the antennal transcriptomes of the aphid species Megoura crassicauda were sequenced, and expression level analyses of M. crassicauda odorant receptors (ORs) were carried out.  To investigate the chemoreception mechanisms that M. crassicauda uses to detect HIPVs, we performed in vitro functional studies of the ORs using 11 HIPVs reported to be released by aphid-infested plants.  In total, 54 candidate chemosensory genes were identified, among which 20 genes were ORs.  McraOR20 and McraOR43 were selected for further functional characterization because their homologs in aphids were quite conserved and their expression levels in antennae of M. crassicauda were relatively high.  The results showed that McraOR20 specifically detected cis-jasmone, as did its ortholog ApisOR20 from the pea aphid Acyrthosiphon pisum, while McraOR43 did not respond to any of the HIPV chemicals that were tested.  This study characterized the ability of the homologous OR20 receptors in the two aphid species to detect HIPV cis-jasmone, and provides a candidate olfactory target for mediating aphid behaviors.  

Pea aphid, Acyrthosiphon pisum, is a serious pest of many different leguminous plants, and it mainly relies on its odorant receptors (Ors) to discriminate among host species.  However, less is known about the role that Ors play in the host plant location.  In this study, we identified a novel conserved odorant receptor clade by phylogenetic analysis, and conducted the functional analysis of ApisOr23 in A. pisum.  The results showed that the homologous Ors from A. pisum, Aphis glycines and Aphis gossypii share 94.28% identity in amino acid sequences.  Moreover, conserved motifs were analyzed using the annotated homologous Or23 from eight aphid species, providing further proof of the high conservation level of the Or23 clade.  According to the tissue expression pattern analysis, ApisOr23 was mainly expressed in the antennae.  Further functional study using a heterologous Xenopus expression system revealed that ApisOr23 was tuned to five plant volatiles, namely trans-2-hexen-1-al, cis-2-hexen-1-ol, 1-heptanol, 4´-ethylacetophenone, and hexyl acetate.  Among them, trans-2-hexen-1-al, which is one of the main volatile organic compounds released from legume plants, activated the highest response of ApisOr23.  Our findings suggest that the conserved Or23 clade in most aphid species might play an important role in host plant detection.

Genes involved in chemosensation are essential for odorant-mediated insect behaviors.  Odorant receptors (ORs) bind and respond to pheromones and plant volatiles, regulating insect behaviors such as mating and host-plant selection, while ionotropic receptors (IRs), which are present at lower levels in insects than ORs, influence ion channels, especially in agricultural pests.  Asian corn borer, Ostrinia furnacalis, is the main pest of maize that causes huge economic losses in Asia.  Twenty-one OfurIRs have been identified, but none has been characterized.  In this study, tissue-specific expression profiling, phylogenetic analysis, and electroantennography (EAG) analysis were applied to characterize the evolution, expression, and the potential function of OfurIRs.  It was found that 20 OfurIRs were highly expressed in the antennae, except for OfurIR75p3, whereas 10 and nine OfurIRs were highly expressed in the proboscis and genitalia, respectively, indicating that these OfurIRs were functionally associated with feeding and oviposition.  EAG results showed that seven acids elicited responses in the antennae of O. furnacalis and that 2-oxopentanoic acid displayed a significant female-biased response.  Combined with the phylogenetic analysis, 10 OfurIRs in clade 4 were roughly predicted to be candidate receptors for 2-oxopentanoic acid and other tested acids.  These results provide basic information about OfurIRs and may help advance the knolwedge on the olfactory system of O. furnacalis. 

(E)-β-Caryophyllene is a sesquiterpene compound widely distributed in plants and functions in plant defence.  However, little is known about the sequence and function of (E)-β-caryophyllene synthase in lima bean (Phaseolus lunatus).  Here, we report a new full-length cDNA (PlCAHS) encoding (E)-β-caryophyllene synthase, a possible key enzyme of plant defence.  The cDNA of PlCAHS contains an open reading frame of 1 761 bp, encoding a protein of 586 amino acids with a predicted mass of 67.95 kDa.  The deduced amino acid sequence shows 52% identity with sesquiterpene synthase MtCAHS of Medicago truncatula.  Based on phylogenetic analysis, PlCAHS is classified as the terpene synthases (TPS)-a subfamily.  The recombinant enzyme, expressed in Escherichia coli, catalysed the formation of a major product (E)-β-caryophyllene (82%) and a minor product α-humulene (18%) from farnesyl diphosphate.  Real-time quantitative PCR (qRT-PCR) analysis found that the PlCAHS transcript was significantly up-regulated in leaves after treatment with spider mites and alamethicin (ALA), suggesting its ecological function in plant defence.  

Strategies for insect population control are currently targeting chemical communication at the molecular level. The diamondback moth Plutella xylostella represents one of the most serious pests in agriculture, however detailed information on the proteins mediating olfaction in this species is still poor. This species is endowed with a repertoire of a large number of olfactory receptors and odorant binding proteins (OBPs). As a contribution to map the specificities of these chemical sensors in the moth and eventually unravel the complexity of chemodetection, we have measured the affinities of three selected OBPs to a series of potential odorants. Three proteins are highly divergent in their amino acid sequences and show markedly different expression profiles. In fact, PxylOBP3 is exclusively expressed in the antennae of both sexes, PxylOBP9 is male specific and present only in antennae and reproductive organs, while PxylOBP19, an unusual OBP with nine cysteines, is ubiquitously present in all the organs examined. Such expression pattern suggests that the last two proteins may be involved in non-chemosensory functions. Despite such differences, the three OBPs exhibit similar binding spectra, together with high selectivity. Among the 26 natural compounds tested, only two proved to be good ligands, retinol and coniferyl aldehyde. This second compound is particularly interesting being part of the chemical pathway leading to regeneration of lignin, one of the defense strategies of the plant against insect attack, and might find applications as a repellent for P. xylostella and other pests.

The nicotinic acetylcholine receptors (nAchRs) are cholinergic receptors that form ligand-gated ion channels by five subunits in insect and vertebrate nervous systems. The insect nAChR is the molecular target of a class of insecticides, neonicotinoids. Here, we identified and cloned 11 candidate nAChR subunit genes in Acyrthosiphon pisum using genome-based bioinformatics combined modern molecular techniques. Most A. pisum nAChRs including α1, α2, α3, α4, α6, α8, and β1 show highly sequence identities with the counterparts of other insects examined. Expression profiles analysis showed that all subunit genes were expressed in adult head. At least two subunits have alternative splicing that obviously increase A. pisum nicotinic receptor diversity. This study will be invaluable for exploring the molecular mechanisms of neonicotinoid-like insecticides in sucking pests, and for ultimately establishing the screening platform of novel insecticides.