Friend or foe: Buy the right creatures to police your plants

It's a bug-eat-bug world out there, and gardeners choosing environmentally friendly controls over chemical pesticides should be able to distinguish insect friend from insect foe.

They also should know the difference in insect diets before buying hungry hordes of predators. Many of these beneficial organisms have specific tastes.

There are two kinds of insects effective for defending yards against infestations: predators and parasites. Predator bugs feed directly on other bugs. Parasitoids deposit their eggs onto or inside other soft insects. The larvae eat their way to adulthood through their crop-damaging hosts, killing them as they grow.

Many beneficial organisms may already be foraging in your yard, working to eliminate any invading pests. That would include spiders, which consume anything caught in their webs, and dragonflies, which are celebrated mosquito feeders.

You can encourage the natives to remain and the imports to hang around by providing sustained supplies of food, water and cover. You also might consider eliminating the use of "zapper lights" that electrocute more beneficial insects than pests, according to a University of Delaware study.

Finally: "Think first, spray last," the Maine Department of Agriculture suggests. That's particularly the case with the broad spectrum chemicals, which are capable of killing everything in the area from butterflies to honeybees.

Here's a sampling of commercially available insect predators:

• Ladybugs, ladybird or lady beetles: Efficient predators as adults or larvae. They consume a variety of pest insects, from aphids to mites. Ladybugs are migratory, however, and seldom linger without a steady food supply. Costs vary with suppliers, so shop around. Average prices run $10 per 1,500 adults or around $50 for 18,000. "For home use, 1,500 usually is enough for one application in a small greenhouse or garden," according to Nature's Control, a mail-order supplier based in Medford, Ore.

• Green lacewings: Lacewing larvae are extremely effective against aphids, thrips and caterpillars. Adults prefer pollen and nectar but with the proper habitat, may remain long enough to deposit eggs, providing the cadre for a resident population. Prices for eggs in cups or cards go about $14 per 1,000. Costs run higher for the larvae, or around $35 per 1,000. Nature's Control suggests a typical release rate ranging from 5,000 to 50,000 eggs per acre and from 1,000 to 5,000 per acre for larvae.

• Predatory mites: Great for greenhouses, where they'll dine on some of their more troublesome cousins, like spider mites and thrips. Costs run high for beneficial mites because they're so perishable, or around $50 per 2,000.

• Pirate bugs: Small black and white insects that forage for thrips, mites and many varieties of insect eggs. Use 100 to 2,000 per acre, depending upon the degree of the infestation. Prices: Around $40 per 100; $200 per 1,000.

• Mantids: Praying mantis are fun to watch but are losing favor with gardeners because they're so indiscriminate in what they hunt.

"Lots of companies sell praying mantis, but primarily the Chinese mantis which are large," said Doug Tallamy, an entomology professor at the University of Delaware and author of "Bringing Nature Home: How Native Plants Sustain Wildlife in Our Gardens." "But then the only thing they eat is large insects. People buy them to eat aphids and they're not attracted to them. They like honeybees better."

Mantids usually are sold in their natural egg cases, each of which can produce 100 to 200 insects. Prices start around $5 per case.

And then there are the egg-laying parasites, which include these home gardener favorites:

• Beneficial wasps: Trichogramma and others, which are parasites of whiteflies and a variety of leaf-eating caterpillars. These wasps are extremely small in size and don't sting. They're usually shipped as pupae in host eggs. Suppliers suggest using at least 5,000 insects for 5,000 square feet, depending upon the severity of the infestation. Pricing runs about $12 for three squares.

• Aphid parasites: Another good biological choice, especially for greenhouses. They lay their eggs inside aphids and the new adults fly out through holes cut through their hosts. They are shipped as near-hatchlings or as adults in containers that you shake onto infested leaves. Figure about $70 per container of 500.

For taking the fight underground:

• Beneficial nematodes: Microscopic-sized roundworms, many of which feed on bacteria, fungi and other insects. Certain predator nematodes are good weapons against leaf-shredding Japanese beetle grubs, fire ants or such turf-damaging grubs as June bugs and crane fly larvae. Packaged on sponges; figure 5 million per application for a 2,000 sq.ft. lawn. About $20 per five million.