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Don't just fight the enemy alone--send for reinforcements. That's the strategy employed by a team of British and Kenyan scientists against corn pests. In tomorrow's issue of Nature they report that molasses grass planted in corn fields significantly reduces crop damage by repelling destructive moths and summoning the pests' insect enemies.

Moth larvae (caterpillars) pose a serious threat to subsistance farming of corn and sorghum in Africa, and for centuries, farmers have planted two or more crops in the same field to control such pests. To develop a scientifically-based version, John Pickett, from the Institute for Arable Crop Research (IACR) in Rothamsted, U.K., and his collaborators from IACR and the International Centre of Insect Physiology and Ecology in Nairobi, Kenya, have been testing many different wild and cultivated plants.

Now they report that molasses grass, a plant not normally planted in crop fields, is particularly repulsive to corn pests. Grown in alternate rows with corn, it reduced crop damage to 5%, compared to 39% for a monoculture. This high level of protection was partly due to an unexpected benefit: The molasses grass quadrupled the percentage of caterpillars parasitized by a wasp species that lays eggs inside the pests, ultimately killing them. In the lab, the reseachers extracted the caterpillar-repelling chemical and showed that wasps are drawn to it.

Molasses grass is "a wonderful alternative to synthetic insecticides," says May Berenbaum, an entomologist from the Univeristy of Illinois in Urbana-Champaign. Pickett points out that the method is environentally sound and also affordable for poor farmers. In addition, he says that planting a field with two pest-repelling plants and two pest-attracting "trap crops" should reduce the chances that pests will develop resistance.