Squash Bug
Anasa tristis (DeGeer), Coreidae, HEMIPTERA


BIOLOGY

Adult - This hard, oval-elongate bug is dark brown, mottled with light gray on its back side and mottled yellow on its underside. About 16 mm long, it is flat across its back and gives off a disagreeable odor when crushed. Typical of all true bugs, the mouthparts are needle-like.

Egg - Roughly diamond- or spindle-shaped, each egg is white when first deposited but gradually turns yellowish-brown and finally dark bronze. It is approximately 1.5 mm long and 1 mm wide. Arranged in a checker-like pattern, eggs typically occur on the foliage in masses of 20 to 40.

Nymph - The five nymphal instars range in length from 2.5 to 10 mm. The first instar is green with rose-colored legs, antennae, and head. These appendages darken in a few hours. Subsequent instars are grayish-white with dark heads, legs, and antennae. The last two instars have noticeable wing pads.


BIOLOGY

Distribution - Squash bugs occur from Canada into Central America and can be found throughout the U.S. Within vegetable gardens, they usually hide under leaves or around the base of plants. These bugs characteristically shy away or move to cover when approached.

Host Plants - All cucurbit vine crops are subject to squash bug infection. The bugs prefer squash, pumpkin, cucumber, and melon, in that order. Hubbard, winter, and marrow squash are often heavily infested.

Damage - Feeding in colonies, adults and nymphs pierce vines with their needle-like mouthparts. While feeding, they inject a toxic substance into plants. As a result, vines quickly turn black and dry out. This aspect of squash bug damage superficially resembles bacterial wilt symptoms. Small plants and individual runners of large vines are often destroyed. When infestations are heavy, fruit may not form. If fruit does develop, bugs may congregate and feed on unripe fruit itself.

Life History - Squash bugs overwinter as unmated adults under plant debris or other suitable shelter. When cucurbit vines start to run in spring, squash bugs fly into gardens and mate. Over a period of several weeks, eggs are laid on undersides of leaves, typically in the angles formed by leaf veins. One or 2 weeks later, depending on the temperature, nymphs hatch from the eggs and begin to feed. Four to 6 weeks pass before nymphs develop into adults. Because of the prolonged egg-laying period, nymphs and adults are present throughout summer. Feeding continues until frost forces adults into hibernation. One generation occurs each year.


CONTROL

Good cultural practices help prevent serious squash bug damage. Proper fertilization of vines produce a vigorous crop better able to withstand insect attack. The planting of resistant squash varieties such as Butternut, Royal Acorn and Sweet Cheese also reduces squash bug problems. Removal and destruction of crop debris after harvest eliminates some potential overwintering sites for squash bugs.

In small gardens, adult squash bugs and leaves with egg masses can be handpicked and destroyed. The bugs can also be trapped by placing small boards near the host vines. Squash bugs gather under the boards at night and are easily collected and destroyed the next morning.

Should a significant infestation develop, insecticide recommendations and rates can be found in the current North Carolina Agricultural Chemicals Manual.

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