Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/2/2006
Publication Date: 9/1/2006
Citation: Carroll, M.J., Schmelz, E.A., Meagher Jr, R.L., Teal, P.E. 2006. Attraction of Spodoptera frugiperda (Lepidoptera: Noctuidae) larvae to volatiles from herbivore-damaged maize seedlings. Journal of Chemical Ecology. 32:1911-1924. Interpretive Summary: Plants attacked by caterpillars emit volatile chemicals that serve as indirect plant defenses through the attraction of parasitoids and other natural insect herbivore enemies. Pest-induced increases in crop plant volatiles may also influence caterpillar behavior yet this direct interaction is poorly understood. Scientists at the Center for Medical, Agricultural, and Veterinary Entomology in Gainesville, Florida have discovered that fall armyworm caterpillars prefer odors from attacked corn plants over odors from unattacked corn plants. Importantly, at least one of the two main volatile chemicals induced by caterpillar attack is highly attractive to fall armyworm caterpillars, more so than the odors of unattacked plants. By manipulating release rates of the volatile linalool, supplemented plants were made more attractive to fall armyworm caterpillars than un-supplemented plants. An understanding of the chemical basis of caterpillar attraction to host plants may enable improved trap crop strategies to lure pests away from valuable plants or tissues and also improve the efficacy of natural enemy attack on pests.
Technical Abstract: Plants respond to insect attack through the induction of volatiles that function as indirect plant defenses through the attraction of natural enemies to the herbivores. Despite the fact that volatiles are induced in response to caterpillar attack, their reciprocal effects on the host location behaviors of the same foraging herbivores are poorly understood. We examined orientation responses of sixth instar fall armyworm (FAW; Spodoptera frugiperda (Smith)) to odors from herbivore-damaged and undamaged maize seedlings (Zea mays var. Golden Queen) in y-tube olfactometer bioassays. While both damaged and undamaged maize seedlings were attractive compared to air, sixth instars preferred odors from damaged maize seedlings over odors from undamaged maize seedlings. GS-MS analysis of plant volatiles revealed that linalool and 4,8-dimethyl-1,3,7-nonatriene were the major volatiles induced by sixth instar FAW herbivory six hours after initial damage. Given its prominence in induced plants and established attractiveness to adult FAW, linalool was evaluated both as an individual attractant and as a supplemental component of whole plant odors. Volatile linalool was more attractive than air to sixth instar FAW over a broad range of release rates. Sixth instars also responded selectively to different amounts of linalool, preferring the higher amount. Sixth instar orientation preferences were readily manipulated through capillary-release of linalool into whole plant odors. Sixth instars preferred linalool over undamaged plant odors, and linalool-supplemented undamaged plant odors over unsupplemented odors, indicating that olfactory preferences of sixth instar FAWs could be changed by alteration of a single volatile component. These results suggest that although many induced volatiles attract natural enemies of herbivores, these defenses may also inadvertently recruit more larval herbivores to an attacked plant or neighboring conspecifics.