The squash bug is one of the most common and troublesome pests attacking squash and pumpkin plants. Both nymphs and adults suck sap from the leaves and stems, apparently also injecting a toxic substance into the plant, causing a wilting known as Anasa wilt of cucurbits. This closely resembles bacterial wilt, a true disease. After wilting, vines and leaves turn black and crisp and become brittle. Small plants are killed entirely, while larger plants may have several runners affected. Squash bugs are often found in large populations, congregated in dense clusters on vines and unripe fruits. Sometimes no fruits are formed as a result.

Description:

Adult squash bugs are rather large, about 12 mm (1/2 inch) long and approximately 1/3 as wide. Adults are winged, brownish black, sometimes mottled with gray or light brown and flat-backed; they give off a disagreeable odor when crushed. The nymphs are whitish to greenish-gray with black legs. Squash bugs vary in size from tiny, spider-like individuals when first hatched to the maturing nymphs which are nearly as large as adults. Young nymphs have red legs and antennae with a green abdomen. After aging a few hours, the red parts become black. Late instar nymphs are a dark, greenish-gray color. Eggs are yellowish-brown to brick red and are laid in groups or clusters.

Squash bug adult (R.A. Casagrande)

Life Cycle:

Unmated adult squash bugs overwinter in the shelter of dead leaves, vines, boards or buildings and fly to cucurbits when vines start to grow. Following feeding and mating, egg laying soon begins. Masses of eggs, each containing about a dozen or more, are usually deposited on the undersides of leaves in angles formed by the veins. Egg laying by the overwintering females continues until midsummer. Eggs hatch in about 10 days or more, and the nymphs pass through 5 instars requiring 4-6 weeks to reach adulthood. Only one generation develops each year and new adults do not mate until the following spring. Squash bugs are secretive in habit. Both adults and nymphs are found clustered near the plant crown, beneath damaged leaves, under clods or in any protective groundcover. They all scamper quickly for cover when disturbed. Because of the protracted egglaying period, all life stages occur throughout the summer months.

Control:

Early detection of adult squash bugs is very important, as they are difficult to kill and can cause considerable damage.

Prevention: If only a few vines are involved, it is best to collect and destroy the bugs and crush their egg masses. Some people place pieces of board or shingles on the ground near the plants to concentrate the number of individuals in an accessible area. Plant remnants may be composted or burned at the end of the year. It is a good idea to select varieties of squash and pumpkin resistant to the squash bug. Since there is only one generation per year, damage can be greatly reduced by keeping vines covered until blossoming begins. Remove the cover for pollination purposes.

Insecticides: If mechanical and cultural controls are inadequate, chemical insecticides registered for garden use can be applied, according to label directions and safety precautions. Repeat applications may be needed.

Adapted from the Ohio State University Extension, 1999. Photo from the Connecticut Cooperative Extension.