Beneficial Insects: Fighting Bugs with Bugs

Stand in the middle of your garden, close your eyes and listen. Mentally screen out any urban noise—planes overhead, barking dogs, traffic, children—and focus on the natural world. You might hear the hum of honeybees, chirping of birds, wind rustling through leaves or tall grass, or rhythmic drips of moving water.

Those familiar sounds bring a feeling of peace, right? But take out a magnifying glass and you’ll find that that sense of calm masks a silent war of sorts. On a microscopic level, pests and predators are battling to the death amid the leaves and soil of our gardens.

That’s not a bad thing. To flip it, predators of pests are actually beneficial. They help keep our gardens healthy by combating pests that might otherwise damage or destroy our crops.

Use of predator insects dates back some 1,700 years, to when citrus growers in China colonized yellow fear ants. The growers linked their trees with bamboo strips so the predator ants could more easily move from one infestation to the next.

Most of us were introduced to beneficials when we were children, via ladybugs. The cute, round bugs are real charmers. However, their ability to annihilate pests should not be underestimated. Indeed, the importation of Australian ladybird beetles to Southern California in the 1880s saved the fledgling citrus industry from a deadly wipeout threatened by cottony cushion scale.

Getting Started

Today, aphids are often the gateway pest that sparks interest in beneficial insects. Ron Whitehurst, a pest control advisor and co-owner of Rincon-Vitova Insectaries, a company in Ventura that produces and distributes insects and other organisms, supplies and tools for biological control of pests, advises first simply blasting aphids with water. Next up, a soapy solution of an ounce and a half of liquid soap to a gallon of water.

If neither works, he then suggests releasing beneficial insects. Ladybugs are a good start, especially early in the year when other beneficials might not be as active. They are voracious eaters: a single black- and orange-spotted alligator-shaped larva may eat 400 aphids before it pupates, while an adult may eat 5,000 aphids during its yearlong life.

When temperatures warm up, green lacewings can be even more effective. The larvae devour not only aphids, but caterpillar pests, eggs and young larvae of Colorado potato beetles, flea beetles, leafhoppers, mealy bugs, psyllids, scales, spider mites, thrips and whiteflies. As a bonus: Unlike ladybugs, green lacewing larvae can’t fly away. Also, it’s interesting to note that once the larvae mature to gossamer-winged adults, they become vegetarians, supping only on pollen and nectar.

Beyond Aphids

To conquer spider mites, thrips, moths and other pests, a second tier of beneficial insects awaits.

Neoseiulus californicus is a predator that battles spider mites as well as persea mites, which are especially pernicious bugs that suck the chlorophyll from avocado leaves and eventually defoliate the trees.

Minute pirate bugs go after western flower thrips and onion thrips. For a one-two punch, Ambleyseius cucumeris tackles thrips on the upper part of a plant, while Hypoaspis miles is a soil-dwelling mite that feeds on thrips as they drop on the soil to pupate.

Trichogramma wasps are parasitic insects that lay their eggs within the eggs of over 200 pest moth species. The trichogramma larvae eat the innards of the pest eggs, pupate, then emerge as winged adults, ready to lay ever more eggs. The wasps are especially effective against cabbage caterpillars and worms.

Creating a Habitat

You can grow your own beneficial insects by the way you garden. To entice beneficials in the first place, or to encourage them to stick around after they’ve devoured your pests, sustenance is a must.

The trick is to plant plants that provide a succession of pollen and nectar year-round. The patch can be left a little weedy or wild and should never be sprayed.

Look for plants that bear umbel-shaped flowers that make nectar readily available, such as cilantro, dill, fennel and anise.

Other herbs to sustain beneficials include angelica, anise hyssop, borage, caraway, chamomile, marjoram, oregano, parsley, sage, teucrium, thyme and yarrow. Native plants include milkweed, saltbush, coyote brush, wild lilac, buckwheat, toyon, bladder pod and coffeeberry.

A handful of miscellaneous plants includes golden marguerite, bell beans, black-eyed peas, bachelor’s buttons, corn, cosmos, sweet alyssum, yellow sweet clover, sunflowers and white clover.

Lending a Hand

After you’ve built up an ecosystem and colonized beneficials in one spot, it’s easy to move them to wherever trouble is brewing by spraying an attractant.

For instance, if aphids are massing on your broccoli, Whitehurst advises mixing equal parts sugar and dried brewer’s yeast with water. Spray the solution as large droplets to simulate honeydew, which should then draw in aphid predators, such as lacewings, ladybugs and hoverflies.

Helping Combat the Enemy

While beneficial insects dominate their prey, they are vulnerable to ants. “Ants collect the honeydew, the sugary poop from aphids, whitefly, scale,” Whitehurst said. “If they’re working the plants, they will be collecting that honeydew and driving off the beneficial insects that are trying to eat the pests that are generating their candy.”

Controlling ants, then, is an important aspect of supporting and maintaining your beneficials. Whitehurst recommends buying or mixing up a borate-based bait. The ants will eat the bait, take it back to their colonies and perish.