Green lacewing – one of the good guys

Pitting predators against pests

By Cindy Ratcliff

When the Orlando office of ValleyCrest Landscape Companies faced an outbreak of chilli thrips, they didn’t send in trucks with tanks of pesticides, they called in an army: thousands of entomopathogenic nematodes.

The result? These natural enemies of the chilli thrips are helping keep their populations in check, without the need for a strict regimen of synthetic pesticides.

Using a pyrethroid pesticide actually increased the chilli thrip population rather than decreasing it, says Barry Troutman, vice president of technical services for ValleyCrest in Orlando, Florida. So, they had to minimize traditional pesticides in this situation to maximize the beneficial insects. Florida has benefited greatly from the introduction of biological pesticides, he says, not only in the treatment of the invasive chilli thrips but also for controlling mealy bugs on hibiscus plants.

Mole cricket – bad guy

“We certainly have respect for the importance of beneficial insects,” Troutman says, “so we only treat when we have problems that they won’t treat.”

While Troutman knows first-hand that biological controls are effective, he recognizes the limitations of them, too, especially in an industry driven by results. Ultimately, says Troutman, the decision to use biological pest control must be weighed against client expectations.

“You have to be able to tolerate some pest damage, and that makes it hard for customers to accept,” he says.

From a cost perspective, he adds, biological controls target a narrow range of insects, while some synthetics cover a variety of pests. “That makes it hard to manage in high-volume landscaping. But in situations where you can focus on a single problem and allow some degree of plant damage, they do work well.”

Environmental appeal

The goal of biological pest control is to use parasitic and predatory insects to reduce undesirable and harmful insect populations, either by introducing natural enemies into the landscape or by nurturing the beneficial insects already there.

Caterpillar -- bad guy

“I’ve always been more in favor of learning to recognize existing local enemies so you don’t work against them,” says Whitney Cranshaw, professor of entomology at Colorado State University. Many times, he says, landscapers will mistakenly wipe out beneficial insects in their attempt to eliminate other insect pests. “Know the key players. Identify them and work to create an environment that appeals to them.”

Common beneficial insects include lady beetles (ladybugs), green lacewings, predatory mites and parasitic nematodes (entomopathogenic nematodes). Lady beetles and green lacewings are general predators that consume a variety of insect pests; predatory mites feed on other mites and thrips; and nematodes target various soil pests including white grubs, mole crickets and caterpillars.

Food is often all the encouragement these local beneficial insects need to give them staying power, but it has to be more than a few isolated plants. You need a large area of host plant material to keep the good guys around for the long term.