Whiff of grass helps kill bugs fast.

Planting mixtures of plants instead of monocultures is one way to foil crop pests. Such interplanting not only makes it harder for the pest to get at the crop, it can take advantage of insect-deterring chemicals produced by other plants.

One such scheme may be useful for growing maize and sorghum in Africa, researchers from Kenya and the United Kingdom report in the Aug. 14 Nature. John A. Pickett and his colleagues at the Institute of Arable Crops Research in Rothamsted and at the International Centre of Insect Physiology and Ecology in Nairobi tested a variety of wild grasses in the field and found that molasses grass (Melinis minutiflora) both repels stem-borer pests and attracts certain wasps. The wasps reduce the pest population by laying their eggs inside the stem borers.

When planted with maize in alternating rows, the molasses grass reduced crop damage significantly. About 5 percent of the intercropped maize plants were damaged, compared to 39 percent in a maize monoculture.

The researchers identified a family of volatile aromatic compounds in the molasses grass that attracts the wasps. The lure seems to be not the smell of molasses but a piney scent.