When a black vine weevil eats a yew leaf, it gets more than food. The same plant that gives the insect nutrients passes on a dose of a powerful chemical that can, when combined with certain pesticides, lead to the bug's death.
The weevils, Otiorhynchus sulcatus, invaded the United States from Europe in the early 1900s and are now a major pest of small fruits like strawberries and ornamentals like rhododendrons and begonias.
Scientists suspected the yew's qualities when they noticed that pyrethroid insecticides killed black vine weevils feeding on yew plants but not weevils on strawberries.
Robert P. Doss, a plant physiologist with the Agricultural Research Service, discovered why.
"We've isolated three chemicals in the yew that act as synergists to increase the effectiveness of pyrethroids," he says.
These are the first insecticidal synergists ever found in the yew, which has been widely studied as a source of anticancer compounds.
Doss works in the ARS Horticultural Crops Research Unit at Corvallis, Oregon. He collaborated with scientists at Oregon State University in Corvallis and Washington State University in Vancouver.
Pyrethroid insecticides are synthetic compounds based on pyrethrins, natural insecticides found in a certain type of chrysanthemum. They are popular because they are less toxic than some other commonly used chemicals.
Pyrethroid-based products often contain a synergist to increase their potency. For example, piperonyl butoxide dramatically increases the potency of insecticides that kill fleas on dogs and cats by disrupting a key enzyme involved in insecticide breakdown by the insect. Piperonyl butoxide is a synthetic version of a compound found in sesame seeds. Doss believes the yew insecticide synergists may work the same way.
The yew compounds have very complicated chemical structures and took nearly a decade to isolate.
"Right now, these chemicals would be prohibitively expensive to manufacture," Doss says. But discovering their structure paves the way for developing cheaper synthetic versions.
Doss' next step is to test the synergist-pyrethroid combination on other weevils, as well as on moths, crickets, and beetles that attack crops.By Kathryn Barry Stelljes, Agricultural Research Service Information Staff.
"A Little Bit of Yew Helps Insecticides" was published in the November 1998 issue of Agricultural Research magazine. Click here to see this issue's table of contents.