Labial and maxillary palp recordings of the Asian longhorned beetle, Anoplophora glabripennis, reveal olfactory and hygroreceptive capabilities

• Published in: Journal of insect physiology 2019-08, Vol.117, p.103905-103905, Article 103905
• Main Authors: Hall, Loyal P., Graves, Fern, Myrick, Andrew, Hoover, Kelli, Baker, Thomas C.
• Format: Article
• Language: English
• Subjects: acetic acid; aldehydes; Animals; Anoplophora glabripennis; appendages; Asian longhorned beetle; Cerambycidae; Coleoptera - physiology; Coleoptera - ultrastructure; Electropalpogram; Electrophysiology; EPG; Female; humidity; insect physiology; insects; Male; mouth; North America; odor compounds; odorant receptors; odors; Olfaction; oviposition sites; Palps; pests; quarantine; sampling; Sensilla - physiology; Sensilla - ultrastructure; Single sensillum recording; Smell; SSR; taste; trail pheromones; trees; USDA; water vapor
• ISSN: 0022-1910; 1879-1611
• DOI: 10.1016/j.jinsphys.2019.103905

Recording electropalpograms of responses to odorants from A. glabripennis palps. [Display omitted] •Maxillary and labial palps respond to various odorants (via EPG and SSR).•Palps respond to water vapor in a dose-responsive manner.•Responses to acetic acid and butyraldehyde indicate likely ionotropic receptors.•Labial palps respond to non-aldehyde/acid odorants, indicating likely odorant receptors.•Palp apical pits are not rigidly concave, but can be flexed into a convex bulge. Electrophysiological recordings from the labial and maxillary palps of the Asian longhorned beetle, Anoplophora glabripennis, revealed their ability to detect several volatile chemicals, including water vapor and acetic acid. The results indicate that these appendages may play a large role in this beetle's assessment of its immediate environment. A. glabripennis is a highly destructive, invasive pest that feeds preferentially on maple — but accepts many other tree species — in North America, warranting USDA quarantine zones and an eradication program. While control and sampling techniques are being developed for this insect, a better understanding of its sensory capabilities is helpful. Electropalpograms (EPGs) revealed that both the maxillary and labial palps are highly sensitive to changes in humidity, indicating the presence of hygroreceptors and the likely important role of humidity in such things as feeding and finding water or oviposition sites. Strong EPG responses to a narrow set of volatile chemicals indicate that olfactory sensory neurons (OSNs) on the palps may be tuned to a small number of volatile compounds. The types of odorant molecules eliciting responses indicate that there are likely both odorant receptors (ORs) as well as ionotropic receptors (IRs) expressed on the OSNs, enabling palp OSNs to be able to respond to acids and aldehydes such as acetic acid and butyraldehyde. There were no significant EPG responses to this species' trail-sex pheromone components, which may indicate that the trail pheromone is primarily perceived via gustatory receptors contacting the substrate. These results indicate that the palps have a role in the beetle’s assessment of its immediate environment underfoot, and that the sampling of surface odors and humidity via mouth parts may be important to this species' success.