Attractiveness of tobacco volatiles induced by Helicoverpa armigera and Helicoverpa assulta to Campoletis chlorideae

The attraction of Helicoverpa armigera- and Helicoverpa assulta-induced and mechanical damage-in- duced tobacco volatiles to Campoletis chlorideae was investi-gated, and the induced volatiles were analyzed. In wind- tunnel, C. chlorideae was strongly attracted by herbivore- induced tobacco volatiles. Mechanically damaged tobacco leaves, whether treated with caterpillar regurgitant or water, were more attractive to the parasitoid than undamaged to-bacco leaves. GC-MS analysis revealed that only 4 com-pounds were released from undamaged tobacco leaves, whereas 13 compounds were commonly emitted from herbi-vore-infested and mechanically damaged tobacco leaves. Compound β-pinene was specifically induced by the infesta- tion of H. armigera, and (Z)-3-hexenal was only induced by the infestation of H. armigera and H. assulta, whereas hexyl acetate was only induced by mechanical damage. Tobacco leaves infested by H. armigera and H. assulta released larger amounts of volatiles than undamaged tobacco leaves did. Tobacco leaves treated with artificial damage plus caterpil- lars regurgitant or water emitted the same levels of volatiles, which were higher than that emitted by undamaged tobacco leaves. The emission amounts of single compounds were also different between differently treated plants. The differences were large between herbivore-induced and mechanical dam-age-induced compounds, and small between H. armigera- and H. assulta-induced compounds, and among compounds emitted from mechanically damaged plants treated with wa-ter or caterpillar regurgitant.

Behavioral and olfactory responses of grasshopper hatchlings, Melanoplus sanguinipes, to plant odours and volatile compounds

Behavior and olfactory responses of grasshopper hatchlings, Melanoplus sanguinipes (F.), to odours from plant foliage and volatile compounds were tested using a glass Y-tube olfactometer and electroantennogram (EAG)techniques respectively. In single choice trials, newly hatched hoppers were much more sensitive to the odour from intact leaves and chopped foliage of ryegrass and wheat than other plants. Chopped sorghum leaves, but not stem-cut sorghum,were also significantly attractive. The orientation responses of grasshopper hatchlings to these plants were highly consistent with those of last instar hoppers and adults. When ryegrass was employed as the control, the odour from stem-cut alfalfa was more attractive. There was no significant difference in hopper orientation responses to the odours from chopped seedlings of sorghum, alfalfa, wheat or ryegrass.However, significantly more hoppers preferred the chopped ryegrass control to chopped Louisanna sage. Measurement of the EAG response of first instar hoppers to these plant odours showed that the odour of Louisanna sage elicited the greatest response amplitudes. In olfactory tests using different volatile components, Z-3-hexenol, E-3-hexenol,Z-hex-3-enyl acetate, E-2-hexenal and hexenal gave greater EAG responses than geraniol and 1-octen-3-ol. These results are also consistent with comparable data from adults. Newly hatched grasshoppers had similar EAG response profiles to plant materials and chemicals to those of adults, although the absolute EAG values of young hoppers were much lower than those of adults. Therefore, newly hatched hoppers were able to distinguish plants from an air control, and even host plants from non-host plants, and the feeding experience of hoppers probably has little influence on their subsequent ability as adults to identify and locate food plants.