Three odorant binding proteins may regulate the behavioural response of Chrysopa pallens to plant volatiles and the aphid alarm pheromone (E)-β-farnesene

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.