| Semiochemicals of the Asian longhorned beetle (ALB) were studied. Native to Asia and introduced to Europe and North America, this polyphagous xylophage poses a grave threat to forests as it is capable of killing trees across several genera. In N.A., quarantines and eradication programs have been initiated since its 1996 discovery, and a large research effort launched to understand host-plant relations in the USA and China, as well as potential pheromone attractants. A female contact sex pheromone and male-produced sex pheromone were identified, but the potential for practical use is hindered because evidence suggests these sex pheromones are contact and short-range cues, respectively. To investigate potential long-range volatile attractants, gas chromatography coupled electroantennograhy (GC-EAD) was used to screen for insect semiochemicals. A discriminant analysis (DA) of antennally active plant volatiles demonstrated the presence of cis-3-hexen-1-ol, camphene, linalool, delta-3-carene, and trans-caryophyllene discriminated hosts from non-hosts. Using ozonolysis of female extracts, GC-EAD analyses demonstrated that male antennae can perceive three aldehydes which result from the oxidation of female contact sex pheromones Z-9-C23, Z-9-C25, Z-7-C 25, Z-9-C27, and Z-7-C27. Given the diurnal activity of beetles in the crowns of trees, this underlying hypothesis tested: female contact sex pheromones oxidize to form functionalized, volatile sex pheromones. Y-maze olfactometer lab bioassays using ozonized female extracts vs. crude female extracts, and synthetic aldehydes vs. controls suggest that males orient towards female-produced volatiles. Field bioassays in China utilizing flight-intercept panel traps baited with lures containing synthetic aldehydes and host kairomones + linalool oxide captured significantly more beetles compared to controls, and captured significantly more males than females. To further evaluate potential precursors of female pheromones, a DA of cuticular hydrocarbons of beetles grouped by sex, age, and mating status was completed. The results reveal that a tricosene and a tricosadiene discriminate female age by appearing in older females. Z-7-heptacosene, heptacosyne, and a nonacosene discriminate female mating status, since they decline precipitously following mating. Mating behavioral assays, using sample groups from the DA, determined males preferentially mate with 11-17 d virgin female freeze-killed beetles cf other sample groups or extracts. Field bioassays evaluating oxidized virgin female extracts captured more males than females, but overall mean trap catch was not significant. However, these new potential precursors may be important in long-range virgin female mate finding. Finally, a model is proposed for chemically mediated behaviors involved in ALB reproduction. |
