The American cockroach (Periplaneta americana) is an urban pest with a precise chemosensory system that helps it achieve complex physiological behaviours, including locating food and mating. However, its chemosensory mechanisms have not been well studied. Here, we identified 71 putative odorant carrier protein genes in P. americana, including 57 new odorant-binding proteins (OBPs) and 11 chemosensory proteins (CSPs). To identify their physiological functions, we investigated their tissue expression patterns in antennae, mouthparts, legs, and the remainder of the body of both sexes, and determined that most of these genes were expressed in chemosensory organs. A phylogenetic tree showed that the putative pheromone-binding proteins of P. americana were in different clades from those of moths. Two genes, PameOBP24 and PameCSP7, were expressed equally in antennae of both sexes and highly expressed amongst the OBPs and CSPs. These genes were expressed in Escherichia coli and the resultant proteins were purified. The binding affinities of 74 common odorant compounds were tested with recombinant PameOBP24 and PameCSP7. Both proteins bound a variety of ligands. Our findings provide a foundation for future research into the chemosensory mechanisms of P. americana and help in identifying potential target genes for managing this pest.
Artificial Chrysopa pallens release is a well‐known method for suppressing aphids, but it is difficult to establish lacewing populations in the field. Understanding the functions of C. pallens odorant‐binding proteins (CpalOBPs) and behavioural responses of C. pallens to plant volatiles and aphid alarm pheromone (E)‐ß‐farnesene has important implications for population establishment after lacewing release. Based on our previous study, five antennae‐enriched CpalOBPs were selected. Sequence alignment and phylogenetic analysis revealed that these five CpalOBPs were Classic OBPs and separated into different clades. Of them, CpalOBP10 clustered in the same clade with aphid OBP7, which mediates the perception of green leaf volatiles and (E)‐ß‐farnesene. Ligand‐binding assays showed 31 compounds, including plant‐derived compounds, pest‐induced volatiles and (E)‐ß‐farnesene, had high binding affinities for at least one of these five CpalOBPs. Of the 31 compounds, the pest‐induced volatiles (Z)−3‐hexenyl hexanoate and 2‐hexyl‐1‐decanol, used in host location by the black bean aphid, elicited significant attractive behavioural responses from C. pallens. Conversely, (E)‐ß‐farnesene elicited strongly repellent behavioural responses. It is conceivable that C. pallens utilizes plant‐derived compounds, pest‐induced volatiles and (E)‐ß‐farnesene as foraging cues. Our studies provide new insights into the interrelationships amongst C. pallens, its prey and the host plants. Compounds that elicited significant behavioural responses from C. pallens were also identified.
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