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 re stricted mainly to species of Eucalyptus (Myrtaceae). Volatile semiochemica ls possibly involved in host selection and nonhost rejection were identifie d by high-resolution gas chromatography-electroantennography on samples obt ained by air entrainment of foliage from host and nonhost trees. Compounds from the main host E. globulus, active at physiologically significant level s, included 3-hydroxy-2-butanone, 3-methyl-1-butanol, a branched epoxyalkan e, 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 eth yl 3-methylbutanoate, (Z)-3-hexen-1-ol, 1,8-cineole, or limonene. The nonho st Pinus pinaster (Pinaceae) yielded active compounds common to the host sp ecies, including ethyl 3-methylbutanoate, (Z)-3-hexen-1-ol, alpha-pinene, b eta-pinene, p-cymene, 1,8-cineole, limonene, and linalool but, in addition, myrcene, (E)-beta-ocimene, and alpha-cubebene as candidate nonhost cues. T he nonhost Olea europeae (Oleaceae) also shared some active compounds in co mmon with the host species, including 3-hydroxy-2-butanone, 3-methyl-1-buta nol, the branched epoxyalkane, ethyl 3-methylbutanoate, (Z)-3-hexen-1-ol, a lpha-pinene, but an apparent nonhost cue from this species was the homomono terpene (E)-4,8-dimethylnona-1,3,7-triene, plus other compounds so far unid entified.