THE irony is sweet: the smell of the potato plant could spell the end for the
dreaded Colorado beetle, which ravages millions of dollars鈥� 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鈥檚
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鈥檚 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. 鈥淭here鈥檚 never been an attractant for the Colorado beetle
before, so we鈥檙e looking at something brand new,鈥� Dickens told New
Scientist.
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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. 鈥淲e captured three times as many insects in baited as in
unbaited traps,鈥� says Dickens. He expects the results to be published in the
journal Agricultural and Forest Entomology.
This summer, the researchers plan to try a 鈥減ush-pull鈥� 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.
鈥淲hen the Colorado beetle bites the plant, that鈥檚 released from the wound site,
attracting predators,鈥� 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. 鈥淚n Russia, the
problem鈥檚 so bad they can hardly grow potatoes any more,鈥� 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. 鈥淢aybe
there鈥檚 a blend which tells the beetle that the plant is a potato.鈥�
