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Boosting tomato's SOS gets pests killed.

A field test has now shown that making a tomato scream louder brings a horde of bug-hunting parasitic wasps to trash the tomato's attackers.

In the botanical version of "Help! They're eating me," plants release volatile chemicals when caterpillars bite their leaves. Creatures that prey on caterpillars home in on these distress signals. Like ambulance chasers, they rush to the scene.

The recent test demonstrated that spraying a plant hormone on a tomato crop to boost the distress signals pays off, says Jennifer S. Thaler of the University of California, Davis. "This SOS actually results in more herbivores being killed--that's new," she notes.

In a California field infested with beet armyworms, Thaler sprayed jasmonic acid on half the young tomato plants. That hormone, found in plants as diverse as ferns and cotton, triggers the manufacture of insect toxins and SOS signals.

Native parasitic wasps, Hyposoter exiguae, cruise the fields and inject eggs into armyworms. When the eggs hatch, larvae eat the armyworm from inside.

Three weeks after treating the field, Thaler looked for wasp larvae that had killed their armyworms and formed protective cases that look like bird droppings. She found such pupae on about half of the sprayed plants. The body armyworm count in sprayed plots was twice that in control areas, she reports in the June 17 NATURE.

In another experiment, lab-reared caterpillars in cups beside sprayed plants suffered 37 percent more parasitism than those near controls.

Thaler's research "is a very important next step," comments the Department of Agriculture's W. Joe Lewis of Tifton, Ga., who studies ways to incorporate SOS signals into pest control. He says that intriguing as the strategy sounds, he wants to know more about the big picture. For instance, does amplifying the signals crowd wasps into an area with no corresponding profusion of caterpillars, so that it reduces the next wasp generation?

USDA chemist and plant-defense specialist James H. Tumlinson of Gainesville, Fla., notes, "The really interesting part of this is that it was done in the field." Remarking that the strategy holds promise, he says, "This is a really red-hot area."
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Title Annotation:research indicates jasmonic acid protects tomato plants
Author:Milius, S.
Publication:Science News
Article Type:Brief Article
Date:Jun 19, 1999
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