ICIPE repelled and trapped maize stemborers with companion plants, not chemicals

By the 1990s the smallholder maize belt of eastern Africa was losing its staple twice over. Stemborer caterpillars tunnel through maize stems, and Striga hermonthica, an obligate root parasite, attaches to the crop's roots and poisons it within days — poor farmers could not afford insecticides, and decades of breeding and spraying had not reached their fields. The International Centre of Insect Physiology and Ecology (ICIPE) and Rothamsted Research asked a different question: not how to kill the moth, but how to make the maize field a place the moth would not want to be.

The team read the pest's host-finding code. Female stemborers find hosts by volatile blends, so Zeyaur Khan and John Pickett's groups surrounded the crop with signals it could not misread: molasses grass (later silverleaf Desmodium) as an intercrop emitting odors repugnant to moths but attractive to Cotesia wasps, and a Napier grass border that out-competes maize at attracting oviposition. The trap is fatal — Napier sap gums up the larvae, killing over 80% within 15 days. Desmodium plots also emerged with almost no Striga: its root exudates provoke suicidal germination of the parasite.

The economics did the real work. Every input is a seed, not a bottle: Desmodium fixes nitrogen, and both companion plants are high-value dairy fodder, so the 'pest control' pays its own way. Adoption passed 55,000 smallholder households by 2013 with roughly 30% annual growth and a stated target of one million by 2020; a drought-tolerant second generation roughly doubled yields again in drier districts.

Repel moths with one plant, trap and kill them on another

It exploits the moths' own host-seeking chemistry instead of poisoning them, so there is no resistance treadmill and no input the farmer must re-buy.

The trap crop turns the pest's strongest preference into a death sentence: Napier attracts more oviposition than maize, then its gummy sap kills the larvae.

The serendipitous Striga effect was noticed in the field and chased down with chemistry, adding a second problem solved by the same plant.

Companion plants return value — nitrogen, organic matter, dairy fodder — so the technology spreads on farm economics, not on subsidy.

When a pest resists direct attack, find leverage in its own navigation signals. A designed habitat can beat chemistry the users cannot afford, and one plant can solve several problems at once.

Push-pull spread across Kenya, Uganda, Tanzania and Ethiopia and was adapted after the 2016 fall armyworm invasion; a third generation pairs Desmodium incanum with Brachiaria Mulato II for drought. The mechanism kept being refined: a 2025 eLife study from Bern and ICIPE found Desmodium volatiles intercept and kill moths rather than simply repel them — the field results hold while the exact signal biology is still being mapped.