In a quiet Penn State laboratory, something remarkable is happening to corn plants — not from a new chemical spray or a genetically modified seed, but from the lowly cover crop that grew in the soil before them. Researchers there discovered that corn grown in soil once used by pea cover crops sends out a chemical distress signal that literally calls in backup: lady beetles that happily gobble up the very caterpillars threatening the plants.
The study, led by Jared Ali, an associate professor of entomology and director of the Center for Chemical Ecology at Penn State's College of Agricultural Sciences, appears in the journal Basic and Applied Ecology. It zeroes in on cover crops, the plants farmers grow between main growing seasons to protect and enrich the soil — a practice that has been popular for thousands of years but whose hidden defenses were little understood.
The team grew corn in soil conditioned by three different cover crops — pea, radish, and a wheat-rye hybrid called triticale — alongside a control of bare fallow soil. Then they raised fall armyworm larvae (caterpillars that grow into moths) on the plants and watched what happened. The results were striking. Plants grown in pea-conditioned soil released almost twice as much indole, a chemical that primes neighboring plants to defend themselves by boosting stress hormones and defensive compounds. And when lady beetles were given a choice, they significantly preferred to snack on caterpillars feeding on the pea-conditioned corn.
There was a trade-off, though. Those same pea-conditioned plants produced lower levels of benzoxazinoid, a natural toxin that acts as a pesticide, antifungal, and feeding deterrent. In fact, corn in bare fallow soil had roughly twice as much of this natural defense as any other soil. Ali notes this likely reflects how plants allocate resources — a tension scientists still need to study more closely.
For Ali, the real excitement is practical. "This allows me to go into the field and tell growers that the cover crops they select change its potential resistance to pathogens and insects," he said. "That's an insight we didn't have before."
The research is part of Ali's larger mission to rediscover the "fangs" of domesticated plants. He compares modern crops to dogs bred from wolves: as humans selected plants to grow faster, produce more, and taste better, we unintentionally bred out some natural defenses, leaving growers reliant on pesticides. Ali's team is hunting for the defenses that remain.
"If we can put them in the right context, what defenses still remain in our domesticated plants?" he asked. The answer, it seems, is hiding right underfoot — in the soil and the humble cover crops that keep it healthy. Growers already using these familiar techniques may now have a science-backed reason to choose their cover crops wisely, turning a simple farming habit into a natural pest-control strategy.