|Tumlinson Iii, James|
Submitted to: Planta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/20/2003
Publication Date: 11/19/2003
Citation: Rose, U.S., Tumlinson III, J.H. 2003. Volatiles released from cotton plants in response to helicoverpa zea feeding damage on flower buds. Planta. 218:824-832. Interpretive Summary: When caterpillars feed on the leaves of plants, the plants emit odors that attract natural enemies of the caterpillars, including tiny wasps that parasitize the caterpillars. Scientists at the Center for Medical, Agricultural and Veterinary Entomology, USDA-ARS, Gainesville, Florida have been studying how feeding by cotton bollworms, serious pests that feed on the flower buds and fruit of the cotton plant, affect the release of odors by the plant. They discovered that feeding by the bollworms on the cotton squares (flower buds) induces the plant to release the attractive odors from all parts of the plant, including the leaves. Thus, the entire plant responds to damage to squares and sends out a strong chemical signal that attracts natural enemies of the pest. These results indicate that plants are highly capable of defending themselves from attack by herbivorous insects and it should be possible to enhance this quality in agricultural crops like cotton through breeding or genetic modification. This will significantly enhance the effectiveness of biological control methods for managing insect pests of agricultural crops with insect natural enemies.
Technical Abstract: Plants under attack by herbivorous insects defend themselves by actively emitting volatile compounds. After several hours of herbivore feeding on cotton (Gossypium hirsutum) flower buds (squares) the volatile blend emitted by the plant changes, with a number of additional compounds, mostly acyclic terpenes being released. These herbivore-induced volatiles may attract predators and parasitoids to the herbivore-damaged plant. We have found chemical evidence that feeding of Helicoverpa zea larvae on cotton squares for 24 or 48 hours will induce the release of a number of terpenes ((E)-ß-ocimene, linalool, (E)-ß-farnesene, (E,E)- -farnesene, (E)-4,8-dimethyl-1,3,7-nonatriene, (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene), isomeric hexenyl butyrates, 2-methylbutyrates, indole and (Z)-3-hexenyl acetate that are not released in significant amounts from undamaged squares and freshly damaged squares. The release of inducible compounds was not limited to the damaged squares themselves. They were also released systemically from the upper undamaged leaves of the same plant after 72 hours. However, the composition of the blend of systemically released volatiles differed from the blend released by damaged squares. Compounds that were systemically released in significantly higher amounts from undamaged leaves in response to feeding on the squares of the same plant compared to control leaves were (Z)-3-hexenyl acetate, (E)-ß-ocimene, linalool, (E)-4,8-dimethyl-1,3,7-nonatriene, (E)-ß-farnesene, (E,E)- -farnesene, and indole.