Identification of host and nonhost semiochemicals of eucalyptus woodborer Phoracantha semipunctata by gas chromatography-electroantennography

The host range of the eucalyptus woodborer, Phoracantha semipunctata, is restricted mainly to species of Eucalyptus (Myrtaceae). Volatile semiochemicals possibly involved in host selection and nonhost rejection were identified by high-resolution gas chromatography-electroantennography on samples obtained by air entrainment of foliage from host and nonhost trees. Compounds from the main host E. globulus, active at physiologically significant levels, included 3-hydroxy-2-butanone, 3-methyl-1-butanol, a branched epoxyalkane, ethyl 3-methylbutanoate, (Z)-3-hexen-1-ol, alpha-pinene, beta-pinene, p-cymene, 1,8-cineole, limonene, and guaiene. E. camaldulensis gave a similar spectrum of volatiles that also included alpha-terpinene and linalool. The volatiles from E. tereticornis were similar to E. globulus but without ethyl 3-methylbutanoate, (Z)-3-hexen-1-ol, 1,8-cineole, or limonene. The nonhost Pinus pinaster (Pinaceae) yielded active compounds common to the host species, including ethyl 3-methylbutanoate, (Z)-3-hexen-1-ol, alpha-pinene, beta-pinene, p-cymene, 1,8-cineole, limonene, and linalool but, in addition, myrcene, (E)-beta-ocimene, and alpha-cubebene as candidate nonhost cues. The nonhost Olea europeae (Oleaceae) also shared some active compounds in common with the host species, including 3-hydroxy-2-butanone, 3-methyl-1-butanol, the branched epoxyalkane, ethyl 3-methylbutanoate, (Z)-3-hexen-1-ol, alpha-pinene, but an apparent nonhost cue from this species was the homomonoterpene (E)-4,8-dimethylnona-1,3,7-triene, plus other compounds so far unidentified.