Volatile metabolites of willows determining host discrimination by adult Plagiodera versicolora

Abstract

AbstractPlagiodera versicolora Laicharting is a highly damaging leaf beetle foraging on willow leaves. In willow germplasm collections, observation has shown that Salix suchowensis Cheng was severely foraged by this leaf beetle while Salix triandra L. was damage free or only slightly damaged. Results of olfactometer bioassays show that the headspace volatiles from leaves of S. triandra significantly repelled adult beetles, suggesting that this species produces volatile repellents against P. versicolora. S. suchowensis had no effect on the beetles. Gas chromatography-mass spectrometry was carried out to profile the headspace volatile organic compounds and 23 compounds from leaves of the alternate species in significantly different concentrations were detected. The effects of 20 chemical analogs on host discrimination were examined. Olfactory response to these chemicals showed that o-cymene, a S. suchowensis specific constituent, significantly attracted adult P. versicolora. In contrast, cis-3-hexenyl acetate, a constituent concentrated more in S. triandra than in S. suchowensis, significantly repelled beetles. Mixing o-cymene and cis-3-hexenyl acetate in comparable concentrations as in the volatiles of S. suchowensis demonstrated that the latter could mask the attracting effect of the former, causing a neutral response by adult beetles to leaves of S. suchowensis against clean air. In addition, chemical analogs have the same effect as plants when resembling volatile organic compounds in real samples. Two volatile metabolites were detected triggering host discrimination by one of the most damaging insect pests to host and non-host willows. The two metabolites are of considerable potential for use as olfactory signs in managing the beetles.