The piercing-sucking herbivores Lygus hesperus and Nezara viridula induce volatile emissions in plants

Plant volatiles induced by herbivory are often used as olfactory cues by foraging herbivores and their natural enemies, and thus have potential for control of agricultural pests. Compared to chewing insects and mites, little is known about plant volatile production following herbivory by insects with piercing-sucking mouthparts. Here, we studied factors (insect life stage, gender, the role of salivary glands, and type of bioassay used for volatile induction) that influence the induction of plant volatiles by two agriculturally important hemipterans, Lygus hesperus and Nezara viridula. Feeding on intact cotton by virgin females of L. hesperus induced 2.6-fold greater volatile response compared to that induced by mated females, possibly due to increased feeding activity by virgin females. This plant volatile response was associated with elicitors present in the insect's salivary glands as well as to the degree of mechanical injury. Feeding injury by N. viridula females also increased volatile emissions in intact maize by approximately 2-fold compared to control plants. Maize seedlings injured by N. viridula emitted higher amounts of the monoterpene linalool, the sesquiterpenes (E)-beta-caryophyllene, alpha-trans-bergamotene, and (E,E)-beta-farnesene, and the homoterpene (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene, but not amounts of green leaf volatiles, compared to uninjured plants. Emissions from intact maize injured by adult males were lower than those emitted by adult females of the same age and did not differ from those emitted by uninjured plants. Similarly, feeding by virgin female N. viridula followed by excision led to 64% higher quantities of volatiles compared to untreated plants. Volatile emission in excised plants, however, was considerably greater than in intact plants, suggesting that careful consideration must be given to bioassay design in studies of herbivore-induced plant volatiles. Salivary gland extracts of N. viridula led to sesquiterpene emissions approximately 2.5-fold higher than for controls, although no significant differences were observed for green leaf volatiles, monoterpenes, and homoterpenes. These results indicate that L. hesperus and female N. viridula feeding induce volatile production in plants, and that volatile production is affected by gender and life stage of the bug. Although oviposition and mechanical injury by stylets may increase release of volatiles, elicitors from salivary glands of L. hesperus and N. viridula also seem to play a role in the emission of plant volatiles.