By Gene McAvoy
The squash bug (Anasa tristis) attacks squash and other cucurbits throughout Central and North America. Several related species in the same genus coexist with squash bug over most of its range, feeding on the same plants but causing much less injury.
Photo by Whitney Cranshaw
IDENTIFICATION
The adult is dark grayish brown in color, and the abdomen may be marked with alternating gold and brown spots. Adults can live 75 to 130 days, depending on availability and quality of food.
The squash bug attacks nearly all cucurbits, but squash and pumpkin are preferred. The squash bug causes severe damage to cucurbits because it secrets toxic saliva into the plant. The foliage is the primary site of feeding, but fruit can also be fed upon. The foliage wilts, becomes blackened and dies following feeding. The amount of damage occurring on a plant is directly proportional to the density of squash bugs.
SURVIVAL AND SPREAD
Squash bugs have two to three generations per year in warmer regions. The preferred overwintering site seems to be in or around cucurbit fields under crop debris, or in clods of soil. Sometimes adults also are found in adjacent wood piles or buildings.
Eggs are deposited on the lower surface of leaves, though occasionally they occur on the upper surface or on leaf petioles. The elliptical egg is bronze in color. Females deposit about 20 eggs in each cluster. Eggs may be tightly clustered or spread out.
There are five nymphal instars. The nymphal stage requires about 33 days for complete development. First instar nymphs are light green in color but turn increasingly darker gray as they mature from second through fifth instar. The thorax and wing pads are barely noticeable on hatching but become more pronounced with each molt. Young nymphs are highly gregarious, a behavior that fades as the nymphs mature.
MANAGEMENT METHODS
Several natural enemies of squash bug are known, mostly wasp egg parasitoids. The best-known parasitoid natural enemy is Trichopoda pennipes, a brightly colored fly. Flies develop principally in the adult bug, killing it when the fly emerges.
Squash bugs are not typically a severe pest in large-scale commercial production but can be a major problem in small-scale organic operations. Neem and soap sprays directed at young nymphs may provide some control.
Squash bugs will often be found feeding in abandoned plantings, so sanitation and clean cultivation are essential to reduce carry-over populations.
Squash bug adults can be difficult to kill with insecticides. Although adult control can be accomplished if the correct material is selected, it is advisable to target the more susceptible nymphs. Several insecticides are labeled for control.
Pollinators should be considered before insecticides are applied. If insecticides are to be applied when blossoms are present, it is advisable to use insecticides with little residual activity. Apply insecticides late in the day when honeybee activity is minimal.
Consult University of Florida Institute of Food and Agricultural Sciences recommendations for currently labeled insecticides for squash bug control in Florida.