A young maize tassel is opened up to reveal stem borers hidden inside, and damage caused by their feeding, in a farmer's field in Embu district, Kenya. Stem borers are a class of insect pest, made up of a number of moth species distributed around the world, which lay their eggs at night on the underside of emerging leaves of young maize plants. The larvae, or caterpillars, that hatch from the eggs - i.e. the borers - quickly make their way inside the plant, where they feed undisturbed by predators. Young larvae feed on foliar tissue in the whorl, leading to perforations in unfolding leaves, and potential destruction of the growing point, while older larvae burrow into the stem, where they starve the growing plant of nutrients and can cause lodging. They feed extensively on tassels, ears, and stems. Borers' stealthy habits make them one of the most damaging pests for maize in Africa, and yet virtually invisible to farmers, who tend to attribute the damage to their crops to more visible pests. “Many farmers in Kenya don’t even know their maize fields have a stem borer problem, yet these insects cost them some 400,000 tons in lost harvest each year,” says CIMMYT maize breeder Stephen Mugo. Chemical pesticides can control borers, but must be applied soon after planting, and are difficult for resource-poor farmers to afford. “Even farmers who know about stem borers only notice the damage after it’s too late for chemical control. A seed-based technology is what we need,” says Mugo. In ongoing research, CIMMYT is collaborating with the Kenya Agricultural Research Institute (KARI) to develop maize varieties that are resistant to stem borers, and to disseminate these to resource-poor smallholder farmers. “Maize that resists stem borer damage would take the guesswork out of stem borer pesticide usage by eliminating it altogether,” says Mugo. The work is part of the Insect Resistant Maize for Africa (IRMA) project. For more information about stem borers in Kenya and CIMMY

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