NEWS OF THE WEEK are beneficial insects that are harmless to animals and humans, and that are already in use to control caterpillars and other crop pests. After finding a caterpillar, the wasp injects an egg into it. This immediately slows feeding by the caterpillar. Later, the wasp egg develops into a larva that feeds internally on the caterpillar. In their study, the Gainesville scientists scratched the surfaces of two leaves on corn plant seedlings and exposed them to caterpillar oral secretion, a combination of digestive fluids and saliva that is known to induce local terpenoid release. They left two other leaves on each corn seedling undamaged. They found that terpenoids that attract wasps were emitted from the scratched, treated leaves of the corn plants, as expected. However, Turlings and Tumlinson also found significant Corn plants attacked by caterpillars can limited to sites of damage, but that is amounts of terpenoids released from undamaged leaves. activate an extraordinary, sophisticated activated throughout the plant. "This indicated to us that the plant defense mechanism, according to work The USDA team's findings could published last week by U.S. Depart- help improve the effectiveness of was releasing these chemicals through ment of Agriculture researchers. wasps for biological control of insect all the leaves to defend itself," says The attacked plants release volatile pests, and might make it possible to ge- Tumlinson. "It was systemwide, not chemicals from all their leaves—both netically engineer plants that require just in the leaves that were damaged." Tumlinson adds, "There's a factor in undamaged ones and those munched less insecticide protection. The study on by the caterpillars. These chemicals was conducted by entomologist Ted G the saliva or gut of the caterpillar that serve as a kind of distress call, acting as J. Turlings and chemist James H. Tum- induces the damaged plant to begin beacons to attract wasps that then res- linson of USDA's Agricultural Re- producing these compounds." The cue the plant by destroying the cater- search Service (ARS) laboratory in ARS researchers and other groups are Gainesville, Fla., and published in the now seeking to identify this factor. The pillars. Chemical emissions by plants in re- Proceedings of the National Academy of mechanism by which the plants r e spond to local injury by a systemwide sponse to insect attacks have been ob- Sciences [89, 8399 (1992)]. What the corn plants release are vol- response is also still unknown. served before. However, the new study Corn plants may have originally deis apparently the first to show that atile terpenoids used as a signal by a plants can mount a systemic chemical parasitic wasp, Cotesia marginiventris, to veloped the volatile terpenoids for use defense against predators that is not locate caterpillar hosts. The tiny wasps as direct herbivore repellants. Tumlinson believes that parasitic wasps later learned (in an evolutionary sense) to respond to the chemicals as a way to help them find the caterpillars they use as reproductive hosts. One aim of the ARS work is to maximize the wasps' effectiveness as biological control organisms for various crops. Terpenoids and other volatile chemicals that attract wasps are known to be released—in response to injury and caterpillar oral secretions—from lima bean, eggplant, cotton, cowpea, and soybean plants, in addition to corn. So far, however, release of the volatile chemicals has been found only at attacked sites in these other plants. A systemic, plantwide reaction like that of corn has not yet been found. Parasitic wasp approaches caterpillar on corn plant (left), and lays egg inside caterpillar Stu Borman
to simulate normal gravity. Growth of some eggs will be fixed with formaldehyde at various points, and others will be allowed to develop into tadpoles. The astronauts will carry out further experiments middeck on the shuttle, outside the spacelab. For example, adding to the orbiting menagerie, an Israeli Space Agency Investigation About Hornets (ISAIAH) will focus on the effect of weightlessness on combs built by oriental hornets. Mars Observer will continue the exploration of Mars, carried out by U.S. and Soviet spacecraft between 1964 and 1982. The spacecraft's scientific objectives are to determine which elements and minerals are found in surface material; define the topography
and gravitational field; search for a planetary magnetic field; find the distribution, abundance, sources, and destinations of carbon dioxide, water, and dust over a seasonal cycle; and measure the temperature, water, and dust in the atmosphere. Of particular interest is the role water once played on Mars. Its surface has no liquid water now, but there is ample evidence the liquid flowed there long ago. Mars Observer will carry seven instruments. Among them will be a gamma-ray spectrometer to measure the abundance of elements on the surface, and a thermal-emission spectrometer to map surface rock mineral content, frosts, and cloud composition. Richard Seltzer
Attacked corn plants call wasps to the rescue
8 SEPTEMBER 7,1992 C&EN
