Little is known of the reproductive behavior of longhorned beetles (Coleoptera: Cerambycidae) in the subfamily Prioninae. Mallodon dasystomus (Say), the hardwood stump borer, is a widely distributed prionine that is native to the southern U.S. Here, we explored the chemically-mediated mating behavior of M. dasystomus, and tested the hypothesis that males recognize females by a contact pheromone. In mating bioassays, all males tested attempted to mate with females only after contacting females with their antennae. Moreover, all males attempted to mate with solvent-washed dead females treated with as little as 0.15 ± 0.03 female equivalents of conspecific cuticular extracts, confirming that compounds on the cuticle of females are essential for mate recognition. Cuticular hydrocarbon profiles of females contained 13 compounds that were not present in profiles of males. Among the female-specific compounds, two co-dominant methyl-branched alkanes, 2-methylhexacosane (2Me-C(26)) and 2-methyloctacosane (2Me-C(28)), accounted for 17% of the total hydrocarbons. Our strategy for identifying the contact pheromone was to synthesize and test the bioactivity of female specific compounds, starting with the most abundant. In bioassays, males displayed mating behavior in response to synthetic 2Me-C(26) and 2Me-C(28) when tested individually. Furthermore, when these compounds were tested in combination, they elicited the full progression of mating behaviors, suggesting that 2Me-C(26) and 2Me-C(28) make up the contact pheromone. These findings are further evidence of the critical role of contact pheromones in mating systems of longhorned beetles.

Contact pheromones mediate mate recognition and play important roles in mating systems of longhorned beetles (Coleoptera: Cerambycidae). One common bioassay of contact chemoreception in cerambycids involves presenting a freeze-killed female to a male in a Petri dish arena. If the male attempts to mate with the female carcass, it confirms that mate recognition signals are present and intact and behavior is not involved. Cuticular hydrocarbons are then stripped from the female with successive solvent washes, rendering her unattractive to males and also resulting in a crude extract containing the cuticular hydrocarbons. To test the bioactivity of the crude extract, the same female is then treated with the extract and presented again to the male. Males of some species, including Megacyllene robiniae (Förster), respond less readily to reconstituted females than to those same beetles before they were solvent-extracted. In the present study, we test the hypothesis that the contact pheromone of M. robiniae, Z9:C 25 , exists as a layer on the surface of the epicuticle. We used solid phase microextraction (SPME) to sample cuticular hydrocarbons of female beetles after they were freeze-killed, solvent washed, and treated with crude cuticular extracts. We found that extracting cuticular hydrocarbons from females and applying the resulting crude extract back onto the solvent-washed cadaver scrambles the wax layer and decreases the abundance of the contact pheromone presented on the surface of the insect.