PORTLAND— It’s bug against bug as an increasing number of Oregon nurseries switch from chemical pesticides to insect predators to protect their valuable plants.

Nursery managers say sending insects after the spider mites, whiteflies and other creatures that damage shrubs, trees and flowers is often just as effective as chemicals, and it’s much cheaper.

In Clackamas, John Maurer’s Evergreen Growers Supply imports beneficial bugs from a British Columbia insectory and distributes them to several hundred nurseries in the Northwest and beyond.

When he started pitching bugs instead of chemicals at trade shows, he says skeptics would stop at his booth and say, “’You’re doing what? You’re selling bugs? I want to kill them.’ ”

“Now we can’t stop talking about them,” he told The Oregonian.

Using bio-control methods to control pests isn’t new, but the practice largely disappeared after World War II with the advent of powerful chemical pesticides.

The tide has turned at a time when the public has grown more suspicious of chemicals.

“We’re rediscovering what everybody used to know,” said Ron Tuckett, plant protection manager at Monrovia Nursery in Dayton, one of the state’s largest.

The nursery reports pest control savings ranging from 30 to 70 percent, depending on conditions. Though chemicals are required occasionally when pest populations soar, some sections of the nursery haven’t been sprayed in 10 years, Tuckett said.

Doug Koida, co-owner of Koida Greenhouse Inc. in Milwaukie, said using insects reduced his pest-control cost in poinsettias about 50 to 70 percent, while decreasing his employees’ exposure to potentially harmful chemicals. The public approves as well, he said.

“We have to be conscious of our impact on the world, so I like to use beneficial insects when I can,” he said.

Nursery workers deploy predators by shaking them from trays or from plastic jugs that can hold up to 25,000 bugs.

Some, like predatory mites, simply spread out and start eating. Others employ more strategic tactics. A parasitic wasp called Encarsia formosa lays its eggs inside the eggs of whiteflies. The wasp develops inside the host egg, killing it before emerging as a winged adult.

Nursery managers say cost reduction is only one consideration. Sprays sometimes fail to reach pests hiding on the underside of leaves; predators seek them out.

“The real benefit is plant quality,” Tuckett said. “It used to be we would spray every couple of weeks for mites, but we’d still get some defoliation, or blotches. It just didn’t look good.”