Identification and synthesis of homoterpenoids emitted from elm leaves after elicitation by beetle eggs

Egg deposition of the elm leaf beetle Xanthogaleruca luteola on the leaves of the field elm causes the emission of volatiles attracting the parasitoid Oomyzus gallerucae. The present study describes the identification and synthesis of the homoterpenoids: (E)-2,6-dimethyl-6,8-nonadien-4-one, (E)-2,6-dimethyl-2,6,8-nonatrien-4-one, and (R,E)-2,3-epoxy-2,6-dimethyl-6,8-nonadiene. These compounds may be involved in attracting the egg parasitoid.