Plant Volatiles Influence Electrophysiological and Behavioral Responses of Lygus hesperus

Previous laboratory studies have shown that the mirid Lygus hesperus is attracted to volatiles emitted from alfalfa; feeding damage increases the amounts of several of these volatiles, and visual cues can enhance attraction further. The present study tested single plant volatiles in electrophysiological and behavioral trials with L. hesperus. Electroantennogram (EAG) analyses indicated that antennae responded to most plant volatiles included in the test, and that when gender differences were observed, males usually were more responsive than females. Antennal responses to the alcohols ((E)-3-hexenol, (Z)-3-hexenol, 1-hexanol), the acetate (E)-2-hexenyl acetate, and the aldehyde (E)-2-hexenal were among the strongest. Moderate responses were observed for (E)-beta-ocimene, (E,E)-alpha-farnesene, (+/-)-linalool, and methyl salicylate. A dose dependent response was not observed for several terpenes (beta-myrcene, beta-caryophyllene, (+)-limonene, or both (R)-(+)- and (S)-(-)-alpha-pinenes). EAG responses, however, were not always consistent with behavioral assays. In Y-tube bioassays, males did not exhibit a positive behavioral response to any of the compounds tested. Instead, males were repelled by (E)-2-hexenyl acetate, (+/-)-linalool, (E,E)-alpha-farnesene, and methyl salicylate. In contrast, female L. hesperus moved upwind towards (R)-(+)-alpha-pinene, (E)-beta-ocimene, and (E,E)-alpha-farnesene, and showed a negative response towards (Z)-3-hexen-1-ol, (S)-(-)-alpha-pinene, and methyl salicylate. This study emphasizes the use of multiple approaches to better understand host plant finding in the generalist herbivore L. hesperus.