Behavioural and electrophysiological responses of the European corn borer Ostrinia nubilalis to host-plant volatiles and related chemicals

The European corn borer Ostrinia nubilalis (Hubner) (Lepidoptera: Crambidae) is a worldwide pest of maize (Zea mays L.) and other crops. The semiochemicals released by maize plants and structurally-related compounds can be used by adult female O. nubilalis for host-plant location and oviposition. Headspace volatile compounds emitted by watered and water-deprived maize plants are collected and identified by their retention indices and mass spectra. The most abundant compounds from watered plants are limonene, linalool, benzoic acid, indole, beta-caryophyllene and acetophenone, whereas, in water-deprived plants, limonene, acetophenone, hexanoic acid, benzoic acid and indole are dominant. In addition, (E)-4,8-dimethyl-1,3,7-nonatriene, 6-methyl-5-hepten-2-one, anisole and 1-carvone are undetected in the water-deprived plants. Some of the identified compounds show electrophysiological activity (electroantennogram) in the antennae of both sexes, with the responses elicited by tridecane, tetradecane, dodecane, nonanal, decanal and 2-ethylhexanol on males being particularly noteworthy. In a dual-choice olfactometer, adult females show a preference for 2-hexanol, heptanal, methyl salicylate, hexyl acetate, nonanal, methyl dodecanoate, beta-pinene and (E)-2-hexenyl acetate over hexane controls. Tetradecane, linalool, methyl hexanoate, methyl nonanoate, (Z)-3-hexenyl benzoate, tridecane, 2-cyclopentylcyclopentanone, 3-methylbutyl acetate, beta-myrcene and (Z)-3-hexenyl butanoate result in fewer females in the test arm compared with the control arm. No single compound displays an activity similar to watered maize plants, supporting the hypothesis that blends of volatiles in specific ratios are more effective than single volatile chemicals. The results of the present study suggest that methyl salicylate, which elicits also one of the highest electrophysiological responses in female antennae, plays a role in host preference by O. nubilalis females.