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

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.

Olfactory Sensory Neurons of the Asian Longhorned Beetle, Anoplophora glabripennis, Specifically Responsive to its two Aggregation-Sex Pheromone Components.

We performed single-sensillum recordings from male and female antennae of the Asian longhorned beetle, Anoplophora glabripennis, that included as stimuli the two components of this species' aggregation-sex pheromone in addition to various general odorants. We compared the aggregation-sex-pheromone-component responses of olfactory sensory neurons (OSNs) to those of OSNs that responded to a variety of plant-related odorants. In the smooth-tipped, tapered, trichoid sensilla on the most distal antennal flagellomeres nos. 10 or 11 of both males and females, we found OSNs with high-amplitude action potentials that were tuned to the aldehyde and alcohol pheromone components and that did not respond to various plant-related volatiles. Because this OSN type responded to both the alcohol and aldehyde components it cannot be considered to be specifically tuned to either component. These large-spiking OSNs were co-compartmentalized in these sensilla with a second, smaller-spiking OSN responding to plant-related volatiles such as geraniol, citronellal, limonene, 1-octanol, nerol and citral. The large-spiking OSNs thus appear to be a type that will be involved in aggregation-sex pheromone pathways targeting a specific glomerulus in the antennal lobe and in generating pheromone-related behavioral responses in A. glabripennis. In other sensilla located in these distal antennal flagellomeres as well as those located more proximally, i.e., mid-length along the antenna on flagellomere nos. 4-7, we found OSNs in blunt-tipped basiconic sensilla that were responsive to other plant-related volatiles, especially the terpenoids, (E,E)-alpha farnesene, (E)-ß-farnesene, ß-caryophyllene, and eugenol. Some of these terpenoids have been implicated in improving attraction to pheromone-baited traps. Some of these same OSNs responded additionally to either of the two sex pheromone components, but because these OSNs also responded to some of the above plant volatiles as shown by cross-adaptation experiments, these OSNs will not be the types that convey sex-pheromone-specific information to the antennal lobe.

Odorant receptors and antennal lobe morphology offer a new approach to understanding olfaction in the Asian longhorned beetle.

The Asian longhorned beetle Anoplophora glabripennis (Motchulsky) is an exotic forest pest that has repeatedly invaded North America and Europe from Asia, and has the potential to kill millions of trees and cause billions of dollars in damage. Traps baited with an attractive mixture of volatile organic compounds from hosts have been of limited success in monitoring invasion sites. We propose that lures might be improved through studying the olfactory system of adult beetles, especially the gene family of odorant receptors (ORs) and the structure of the antennal lobes of the brain. Here, we report identification of 132 ORs in the genome of A. glabripennis (inclusive of one Orco gene and 11 pseudogenes), some of which are orthologous to known pheromone receptors of other cerambycid beetles. We also identified three ORs that are strongly biased toward expression in the female transcriptome, and a single OR strongly biased toward males. Three-dimensional reconstruction of the antennal lobes of adults suggested a male-specific macroglomerulus and several enlarged glomeruli in females. We predict that functional characterization of ORs and glomeruli will lead to identification of key odorants in the life history of A. glabripennis that may aid in monitoring and controlling future invasions.

Bioreplicated visual features of nanofabricated buprestid beetle decoys evoke stereotypical male mating flights.

Recent advances in nanoscale bioreplication processes present the potential for novel basic and applied research into organismal behavioral processes. Insect behavior potentially could be affected by physical features existing at the nanoscale level. We used nano-bioreplicated visual decoys of female emerald ash borer beetles (Agrilus planipennis) to evoke stereotypical mate-finding behavior, whereby males fly to and alight on the decoys as they would on real females. Using an industrially scalable nanomolding process, we replicated and evaluated the importance of two features of the outer cuticular surface of the beetle's wings: structural interference coloration of the elytra by multilayering of the epicuticle and fine-scale surface features consisting of spicules and spines that scatter light into intense strands. Two types of decoys that lacked one or both of these elements were fabricated, one type nano-bioreplicated and the other 3D-printed with no bioreplicated surface nanostructural elements. Both types were colored with green paint. The light-scattering properties of the nano-bioreplicated surfaces were verified by shining a white laser on the decoys in a dark room and projecting the scattering pattern onto a white surface. Regardless of the coloration mechanism, the nano-bioreplicated decoys evoked the complete attraction and landing sequence of Agrilus males. In contrast, males made brief flying approaches toward the decoys without nanostructured features, but diverted away before alighting on them. The nano-bioreplicated decoys were also electroconductive, a feature used on traps such that beetles alighting onto them were stunned, killed, and collected.