The irony is sweet: the smell of the potato plant could spell the end for the dreaded Colorado beetle, which ravages millions of dollars' worth of potato crops every year. Using powerful aromas extracted from potato leaves, researchers in the US intend to lure the insects to their death.
Joseph Dickens and his colleagues at the US Agricultural Research Service's field station in Beltsville, Maryland, have isolated half a dozen compounds from spud leaves which draw Colorado beetles to their meal. By measuring the strength of signals from electrodes implanted in the beetle's antennae they screened for the most active substances.
The team then prepared a variety of mixtures of these substances to see which blend worked best. "There's never been an attractant for the Colorado beetle before, so we're looking at something brand new," Dickens told New Scientist.
In experiments in the potato fields of Maine last summer, the researchers found blends of two or three leaf substances which worked well. The most successful blends all contained a volatile leaf odour called (Z)-3-hexen-1-yl acetate. "We captured three times as many insects in baited as in unbaited traps," says Dickens. He expects the results to be published in the journal Agricultural and Forest Entomology.
This summer, the researchers plan to try a "push-pull" approach. Working with the ARS team, Randy Alford of the University of Maine has discovered that Colorado beetles detest limonin, a bitter substance found in orange peel. Greenhouse experiments this summer showed that beetles repelled by potatoes treated with limonin are more likely to be attracted by the baited traps.
An additional bonus was the discovery that the leaf odour (Z)-3-hexen-1-ol attracts predatory insects which kill the beetles in the field. "When the Colorado beetle bites the plant, that's released from the wound site, attracting predators," says Dickens. The predators it attracts include the two-spotted stink bug (Perillus bioculatus) and the spined soldier bug (Podisus maculiventris), which pierce the body of the beetle and suck it dry.
New weapons against the Colorado beetle are desperately needed, according to Hans Vissen, an entomologist specialising in the beetles at Plant Research International, a company in Wageningen, the Netherlands. "In Russia, the problem's so bad they can hardly grow potatoes any more," he says.
John Pickett of the Institute of Arable Crops Research in Rothamsted, Hertfordshire, says he is surpised these attractants are so effective, because the same chemicals are produced by other plants. Different proportions of attractants might let insects discriminate between plants, he says. "Maybe there's a blend which tells the beetle that the plant is a potato."
Author: Andy Coghlan
New Scientist issue 19th February 2000
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