Features Agronomy Insect Pests
Fast-growing plants susceptible to insects

March 29, 2010, Irvine, CA – There's a war occurring each day in our fields: plant vs. plant-eating insect vs. insect-eating insect. Research by University of California–Irvine's Dr. Kailen Mooney suggests the outcome, which is of interest to farmers, is a stalemate.

Plant-eating insects, such as the silhouetted caterpillar have played a pivotal role in the evolution of plants. Photo courtesy of Ellen Woods, Cornell University.

For a study published in the journal Science, Mooney and colleagues studied 16 species of milkweed. The scientists sought to determine the relationship among plant growth, plant defence against plant-eaters (e.g., using thorns or toxins), and the protection plants receive from predators such as ladybugs that eat herbivorous insects.

The herbivores – in this case, bright yellow aphids – damage plants; ladybugs can act as bodyguards, helping plants by eating aphids.
The researchers asked: Can plants have it all? Can they grow quickly and defend themselves against herbivores while at the same time solicit protection from ladybugs and other bodyguards?

The answer is no.

Milkweed species that grow quickly are more vulnerable to herbivorous insects, making them more dependent upon insect predators for their survival. In other words, you can be either a hard-to-eat, slow growing plant that doesn't need bodyguards, or a tasty, fast-growing plant that relies on outside protection.

This finding could be important to crop breeders who are trying to develop herbivore-proof, fast-growing crops. "We can breed plants to for fast growth, but if we do that, it appears we're weakening the plants' immunity against herbivores, making them more dependent upon protection from potentially unreliable predators," says Mooney, assistant professor of ecology and evolutionary biology.

And there may not be much that crop breeders can do.

"Milkweed has been evolving for as many as 20 million years. Natural selection favours faster-growing plants and those that easily fight off insects," Mooney says. "If nature hasn't found a way to combine both, perhaps it's something that cannot be done."

Cornell University scientists Rayko Halitschke, Andre Kessler, and Anurag Agrawal also worked on the study, which was funded in part by the National Science Foundation.

Look for a FULL REPORT in an upcoming issue of Top Crop Manager.