|Tumlinson Iii, James|
Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/14/1996
Publication Date: N/A
Interpretive Summary: Methods are needed to make more effective use of natural enemies for biological control of insect pests of plants. Scientists at the Insect Attractants, Behavior and Basic Biology Research Laboratory, Gainesville, FL, discovered that cotton plants, when attacked by caterpillar pests, release volatile chemicals that attract natural enemies of the pests. They also found that the attractive chemicals are released not just from the leaf damaged by the caterpillars, but from the entire plant. Thus, cotton plants under attack become very attractive to natural enemies of their attackers. However, domestic varieties of cotton do not release as much of the chemicals when attacked as do wild varieties. When the mechanism by which the plants produce the volatile attractants in response to insect damage is understood, it should be possible to develop, through breeding or genetic engineering, varieties that will be much more attractive to natural enemies of their attackers. This should facilitate biological control of cotton pests by increasing the rate at which the pests are removed by their natural enemies.
Technical Abstract: Cotton plants, Gossypium hirsutum (L.), attacked by herbivorous insects release volatile chemical signals that attract natural enemies of the herbivores to the damaged plants. We found chemical evidence that volatiles are not only released at the damaged site, but from the entire cotton plant. The release of volatiles was detected from upper undamaged leaves after two to three days of continuous larval damage on lower leaves of the same plant. Compounds released systemically were (Z)-3-hexenyl acetate, (E)-(Beta)-ocimene, linalool, (E)-4,8-dimethyl-1,3,7-nonatriene, (E)-(Beta)-farnesene, (E,E)-(Alpha)-farnesene, and (E,E)-4-8,12-trimethyl- 1,3,7,11-tridecatetraene. All systemically released compounds are known to be induced by caterpillar damage, and are not released in detectable amounts by undamaged plants. Other compounds known to be released by cotton specifically in response to caterpillar damage, indole and isomeric hexenyl butyrates, were not released systemically. However, when undamaged upper leaves of a caterpillar damaged plant were damaged with a razor blade, they released isomeric hexenyl butyrates, and large amounts of constitutive compounds in addition to the previously detected induced compounds. Control plants, damaged with a razor blade in the same way, did not release isomeric hexenyl butyrates, and significantly smaller amounts of constitutive compounds. Indole was not released systemically, even after artificial damage.