In the garden

Know your bad bugs from the beneficial ones


Daily Press (Newport News, Va.)

Bad bugs vs. good bugs — it’s the name of the game when it comes to environmentally friendly gardening.

Knowing which is which can mean a healthy, chemical-free garden as opposed to a chemically dependent garden that may get sicker as time marches on.

“Not all insects are bad, in fact many are quite good, especially in the landscape,” says Dan Nortman, a Yorktown-based extension agent with Virginia Cooperative Extension.

“A ‘diverse landscape’ will attract beneficial insects, which are those insects that provide pollination and pest control services in our yards. The most valuable beneficial insects in most landscapes are those that provide pest control.

“For most insects that provide pest control, there is a larval stage and an adult stage. Larval stages are generally the stage that provides control, feeding on other insects, whereas the adult stage of most beneficial insects feeds on nectar. Therefore, it is important to provide a nectar source for as much of the active growing season as possible. Having flowers that provide nectar will attract beneficial insects, and they will then lay their eggs on plants infested with harmful insects, and the larvae that hatch from those eggs will provide some pest control.”

Some beneficial insects can nectar on roses, camellias and other large flowered plants, but many of them flourish when they have access to small flowers, Nortman said.

Planting mint family herbs, umbellifers, such as dill, fennel, cilantro and Queen Anne’s lace and other plants, like yarrow, helps promote some of the smaller beneficial insects. However, some cultivars of fennel, such as bronze fennel can become invasive, as can Queen Anne’s lace, mint and non-native yarrow.

“There are many more helpful insects than there are harmful ones,” says Kris Braman, professor in the Department of Entomology and interim director Center for Urban Agriculture at the University of Georgia in Griffin.

“Learn to identify the ‘helpful vs. harmful insects’ and tolerate some pest pressure because it provides food to keep the beneficials at home. Conserve beneficials by modifying pesticide use.”

Jan Newton, a native-plant expert in Williamsburg, Va., agrees:

“If a gardener or homeowner sprays insecticide to get rid of ‘bad’ or unwanted bugs, they also kill the beneficial bugs along with butterflies and bees that help pollinate flowers and crops,” says Newton, a member of the John Clayton Chapter, Virginia Native Plant Society.

Here are the most common beneficial insects, according to Newton, Braman and Nortman:

•  Ladybugs. They are voracious predators on soft-bodied insects, such as aphids, mealybugs, whiteflies, and even small caterpillars. They are particularly beneficial because they feed on pest insects as larvae and as adults. Adults are also nectar feeders.

•  Lacewings. They are small delicate green or brown insects as adults, and voracious predators of aphids, scales and other soft-bodied insects as larvae. The green lacewing lays its eggs on the surface of the leaf, at the end of a silken strand. They do this because the larvae are such voracious predators that the first one to hatch would cannibalize a significant amount of the other eggs. Brown lacewings are a related separate species that does not lay its eggs on silken strands. As a consequence, they are much more rare. Adults lacewings are most often nectar feeders.

•  Syrphid flies. Also known as hover flies, they are important predators of soft-bodied insects as larvae. The larva is a large green maggot, and is often spotted feeding in aphid colonies. The adult is a bee mimic, with yellow and black stripes on the abdomen that is seen hovering around flowers, where it is nectaring. The difference between a bee and a hover fly is that the hover fly has 2 wings and bees have 4 wings, but most people probably won’t get close enough to notice.

•  Predatory bugs. Assassin bugs and big-eyed bugs prey on bad stuff such as tomato hornworms, thrips and spider mites; nectar and pollen in flowers attract them, and ornamental grasses and shrubs provide them with shelter.

•  Predatory midges. These extremely small flies feed on nectar as adults and aphids and other small, soft bodied insects as larvae. Although they are quite small, they are valuable predators because the adult is able to lay a few dozen eggs in an aphid colony, so there is effective pest control.

•  Parasitoid wasps. They are large to microscopically small wasps that lay their eggs inside other insects. After the eggs are laid, their larvae begin to eat the host insect from the inside. They are completely harmless to people. Some parasitoid wasps are the size of yellow jackets, while most are much smaller. The microscopic Trichogrammatidae are so tiny that they lay their eggs inside other insect eggs, where their larvae feed and develop. Other parasitoid wasps lay their eggs in caterpillars, aphids and grubs.

A common sight for most homeowners is the parasitic wasp seen on the tomato/tobacco hornworm. When you see cotton like “pills” on the outside of a hornworm, it is the result of a parasitoid wasp. What has happened is that a wasp has implanted its eggs into the hornworm. The eggs then develop into larvae, which feed on the inside of the hornworm. When the larvae are ready to pupate, they move to the surface of the insect and form the cottony cocoons that you see.

•  Spiders. Although spiders are icky and often thought of as dangerous, they greatly help prevent bad bug breakouts in the garden, especially among veggie plantings.

•  Dragonflies and damselflies. These flying jewels like many insects, especially mosquitoes.

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