One of my favorite garden insect books is “Good Bug, Bad Bug.” Chock full of helpful information, the book reminds me that the adage, “the only good bug is a dead bug”, isn’t true.
Only 10 percent of all insect species cause problems in our gardens. And even they have a positive role in the environment as pollinators, food for birds and other wildlife, and soil decomposers. The rest either help us keep our gardens beautiful and healthy or are benign, creating no problems for us.
Learning the beneficial species and how to attract them, as well as the destructive ones and how to control them, takes some time and experience, but is doable for the home gardener.
One way to narrow down what insect is causing damage is to learn a bit about insect biology. The insect’s mouthpart determines how adults feed. If the leaves of your plant look like something has been feeding on them, your insect has jaws made for chewing. Some examples of chewing insects that are nuisances in home gardens are grasshoppers, some beetles and earwigs. A second type of insect has an elongated mouthpart that sucks liquid out of the leaf. Common sucking insect pests are aphids, mealy bugs, mites, whiteflies and stinkbugs.
Most insects go through metamorphosis, starting from eggs and developing through one to three stages before becoming adults.
Most of us are familiar with the metamorphosis from caterpillar to butterfly. The larval (caterpillar) stage does the most damage. Examples of larvae that cause problems in our gardens are cutworms, leafrollers, sod webworm and wireworms. Cutworms, the larva of a number of moth species, overwinter in the soil and woodpiles, causing most of their damage in the early spring. They feed primarily at night, emerging around dusk. As their name implies, they feed mostly at the base of young plants, effectively “cutting” off the stems. Leafrollers, another moth larva, are primarily tree fruit pests that earned their name from their way of rolling leaves together to live and feed from. Eggs are laid on branches or twigs, hatching in the spring, when they feed for 4-6 weeks.
The sod webworm is the larva of lawn moths. Feeding at night, they chew off the grass blades at the base. You can find them in the thatch layer, so keeping your lawn thatched reduces your chances of having a sod webworm problem. Evidence of their presence are irregular brown patches in your lawn. Wireworms, the larvae of click beetles, attack root crops such as potatoes and dahlias. Living in the soil, they feed on seeds, underground stems and small roots. Unlike many other larvae, wireworms can take years to reach their adult stage. Crop rotation is an effective means of limiting wireworm damage.
Now let’s meet some of the insects we want to live in our gardens. Predatory beetles and true bugs, lacewings, predatory flies, parasitic wasps and parasitic flies eat many of our most common garden enemies, such as mites, aphids, leafhoppers, scale, whiteflies and mealybugs, among others. These insect friends can be helpful in both their larval and adult stages.
The best way to attract beneficial insects is including a diversity of local native plants in and around your garden and implementing integrated pest management practices that lower the use of synthetic pesticides.
One of your tasks as a home gardener, then, is to be a detective, looking for signs of which insects are out and about. Once you know that, you can make a plan to reduce the population of “bad bugs” and encourage the presence of “good bugs.”
A WSU Master Gardeners of Chelan County column appears weekly in The Wenatchee World. Casey Leigh is one of four columnists featured.