LAUSR

BACKGROUND Although parasitoids can precisely locate hidden gall-inducing insects, the mechanism of host location is still unknown. In this study, our aim was to clarify the olfactory responses of the parasitoid Quadrastichus mendeli to eucalyptus volatiles induced by gall wasp Leptocybe invasa. RESULTS Q. mendeli-preferred volatiles from gall-induced plants compared to those produced by mechanically damaged and undamaged plants. Gas chromatographic-electroantennographic detection (GC-EAD) results demonstrated that 3-carene, decanal, d-limonene, ethanone,1-(4-ethylphenyl)-, p-cymene, and benzene,1-methyl-4-(1-methylpropyl)- from DH 201-2 (Eucalyptus grandis × E. tereticornis) in all treatments elicited significant antennal responses of Q. mendeli. Q. mendeli was repelled at decanal and d-limonene and was attracted to 3-carene, benzene,1-methyl-4-(1-methylpropyl)-, ethanone,1-(4-ethylphenyl), and p-cymene. Quaternary blends containing 3-carene, p-cymene, benzene,1-methyl-4-(1-methylpropyl)-, and ethanone,1-(4-ethylphenyl)- at a ratio of 1:1:1:1 were attractive to Q. mendeli. However, the quaternary blends with added decanal, d-limonene, or both of them demonstrated significant repellence to Q. mendeli. CONCLUSION Our report is the first to demonstrate that volatiles produced from galls induced by L. invasa are attractive to Q. mendeli, which suggests that this parasitoid could utilize herbivore-induced plant volatiles to locate their hosts. The results are beneficial for understanding the function of plant volatiles in host searching of parasitoids to gall-forming insect pests. This article is protected by copyright. All rights reserved.