In the spring and early summer, and again in the fall, it's not uncommon for a hoard of small bugs to be found on a home's siding and window screens. Quite often these are boxelder bugs, which in the fall are seeking a warm place to overwinter between the siding and sheathing on the south-and west-facing sides of a home. There are a number of other home-invading beetles, as well, and fortunately, they are generally not at all destructive to the home—just annoying.
A close examination might show that these invaders are not box elder bugs, but squash bugs. And while squash bugs are equally harmless when found on or in your home, it's a different matter if you are a gardener growing squash or other members of the cucurbit family.
Squash bugs ( Anasa tristis) are found across North America. The adults are about 5/8" in length, with a dark brown or gray color. They do not have the bright orange markings of box elder bugs and are slightly larger than the box elder bug. Squash bugs are true beetles, with hard shells and sucking mouthparts. The spider-like nymphs are tiny, about 1/10" long, and feed voraciously.
Both nymphs and adults suck sap from the foliage and vines of squash, pumpkins, cucumbers, and other cucurbits. While feeding, the insects inject a toxin that causes wilting and eventually can turn leaves black and cause them to die. Squash bugs can kill small plants, but larger plants may recover once the bugs stop feeding. Often, a plant struck by squash bug infestation will not produce fruit. Squash bugs give off an unpleasant odor in large numbers or when crushed.
Adults overwinter under dead leaves other garden debris (and sometimes in the cracks in your home's siding) then emerge in late May and June when temperatures begin to warm. Immediately the adults begin to feed and mate, and egg-laying continues until midsummer, with the eggs laid on the underside of leaves of squash, cucumbers, and related plants. After one to two weeks, the eggs hatch and the nymphs immediately feed on plants. There is usually only one generation per growing season, but because the egg-laying period is so long, the pest is found in all stages throughout the summer. This long breeding season, and the fact that it is both the adults and the nymphs which damage plants, is what leads to such extensive damage.
Organic Controls for Squash Bugs
- Plant resistant varieties of vegetables when you can find them.
- If only a few plants are affected, handpick all stages from the undersides of leaves.
- Use floating row covers when the seedling is young. More mature plants can usually tolerate some squash bug damage.
- Diatomaceous earth can be dusted lightly over crops wherever pests are found. The sharp particles will repel the insects.
- Use Need oil every seven days.
- If the damage is excessive, treat the undersides of leaves with a fast-acting organic insecticide.
- Dispose of infested plants shortly after harvest to reduce the number of overwintering adults.
If You Use Chemical Pesticides
There are a number of synthetic pesticides that will control squash bugs, but they should be a last resort after organic controls have been tried. Pesticides containing carbaryl or permethrin are most effective. Use them carefully and according to package directions.