Identification of (-)-beta-caryophyllene as a gender-specific terpene produced by the multicolored Asian lady beetle

This work reports the development and use of techniques for characterizing volatile chemicals emitted by the multicolored Asian lady beetle, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), in an effort to identify the semiochemicals involved in establishment and persistence of overwintering beetle aggregations. Volatiles emitted from live beetles were detected by using whole-air sampling and solid-phase microextraction (SPME). Adsorbed volatiles were thermally desorbed and identified with gas chromatography-mass spectrometry (GC/MS). By comparing the chromatograms of volatiles emitted from live male and female beetles, a sesquiterpene, (-)-beta-caryophyllene, was found only in the females. The identity of (-)-beta-caryophyllene was confirmed by using NIST Library searches, comparing retention times with those of known standards, and by using higher-resolution GC/MS above bench top capability. Although SPME trapping detected a wider array of compounds compared to whole-air sampling, the latter method is better suited for automation. Unattended automated sampling is required for the continuous measurement of targeted compounds under dynamically changing incubation conditions. These conditions, mimicking natural overwintering conditions, are essential to our long-term goal of using this technology to detect and identify the aggregation pheromone of H. axyridis.