Canadian Forest Service Publications
Olfactory receptor neuron responses of a longhorned beetle, Tetropium fuscum (Fabr.) (Coleoptera: Cerambycidae), to pheromone, host, and non-host volatiles. 2015. MacKay, C.A.; Sweeney, J.D.; N.K. Hillier. Journal of Insect Physiology [online early] http://dx.doi.org/10.1016/j.jinsphys.2015.10.003
Issued by: Atlantic Forestry Centre
Catalog ID: 36407
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Longhorn wood-boring beetles (Coleoptera: Cerambycidae) use olfactory cues to find mates and hosts for oviposition. Tetropium fuscum (Fabr.) is an invasive longhorned wood-boring beetle originating from Europe that has been established in Nova Scotia, Canada, since at least 1990. This study used single sensillum recordings (SSR) to determine the response of olfactory receptor neurons (ORNs) in the antennal sensilla of male and female T. fuscum to different kinds of olfactory cues, namely host volatiles, non-host volatiles, the aggregation pheromone of T. fuscum (fuscumol), and an aggregation pheromone emitted by other species of longhorn beetles (3-hydroxyhexan-2-one). Each compound had been previously shown to elicit antennal activity in T. fuscum using electroantennography or had been shown to elicit behavioral activity in T. fuscum or other cerambycids. There have been very few SSR studies done on cerambycids, and ours is the first to compare response profiles of pheromone components as well as host and non-host volatiles. Based on SSR studies with other insects, we predicted we would find ORNs that responded to the pheromone alone (pheromone-specialists), as well as ORNs that responded only to host or non-host volatiles, i.e., separation of olfactory cue perception at the ORN level. Also, because male T. fuscum emerge earlier than females and are the pheromone-emitting sex, we predicted that the number of pheromone-sensitive ORNs would be greater in females than males. We found 140 ORNs housed within 97 sensilla that responded to at least one of the 13 compounds. Fuscumol-specific ORNs made up 15% (21/140) of all recordings, but contrary to our prediction, an additional 22 ORNs (16%) responded to fuscumol plus at least one other compound; in total, fuscumol elicited a response from 43/140 (31%) of ORNs with fuscumol-specific ORNs accounting for half of these. Thus, our prediction that pheromone reception would be segregated on specialist ORNs was only partially supported. Our prediction that females would have more ORNs that responded to fuscumol than would males was also not supported, as there was no difference. The stressed-host volatile linalool elicited the most responses of any compound tested, 43% of all recordings.
Plain Language Summary
The brown spruce longhorn beetle, Tetropium fuscum, is an invasive forest pest from Europe that is established in Nova Scotia where it infests and kills mature, weakened, spruce trees. Like many insects, T. fuscum uses chemical cues like pheromones (to locate mates) and host plant volatiles (to locate suitable trees in which to lay its eggs raise a brood), and it detects these chemicals using specialized cells called olfactory receptor neurons (ORNs) located in its antennae. In other words, the beetle’s antennae act like our nose, sensing “good” or “bad” smells, e.g., plants that are good to eat and plants to avoid. We can apply this knowledge in pest management, e.g., pheromone-baited survey traps are used to determine the spread and distribution of T. fuscum, and broadcast application of fuscumol has been shown to reduce T. fuscum mating success. The objective of this study was to improve our fundamental understanding of how T. fuscum uses its ORNs to perceive different kinds of olfactory cues, namely fuscumol, host volatiles, and non-host volatiles. We found that 15% of ORNs responded only to fuscumol, suggesting these specialized neurons likely connect directly to pheromone-specific regions in the brain. However, we also found that another 16% of ORNs responded to fuscumol plus at least one other compound, suggesting that pheromone-specific ORNs are not the only way in which T. fuscum perceives its pheromone. Linalool, a chemical emitted by stressed spruce trees, elicited the most responses of any compound tested. Research that further improves our understanding of how T. fuscum perceives olfactory cues may lead to new and improved ways of applying pheromones and plant volatiles for use in pest management strategies.