18 February 2000
Sniff could snuff out yellow peril

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 USA intend to lure the insects to their death in traps.

Joseph Dickens and colleagues at the US Agricultural Research Services field station in Beltsville, Maryland, have isolated half-a-dozen compounds from potato leaves which draw Colorado beetles to their meal.

By measuring the strength of signals from electrodes implanted in a beetles antennae they screened for the most active substances.

Mr Dickens told New Scientist magazine that the team prepared a variety of mixtures of these substances to see which blend worked best.

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,” said Mr Dickens.

Now the team plan to try a “push-pull” approach to entice beetles into their traps.

Another researcher discovered that Colorado Beetles detest limonin, a bitter substance found in orange peel.

Greenhouse experiments 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 attracts predatory insects which kill the beetles in the field.

John Pickett of IACR Rothamsted, Hertfordshire, says he is surprised 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 theres a blend which tells the beetle that the plant is a potato.”