The squash bug (Anasa tristis) is a major pest of cucurbit plants, including squash, pumpkins, and gourds. These insects use piercing-sucking mouthparts to feed on plant sap, causing damage that ranges from cosmetic leaf spots to the complete collapse of a young plant. Recognizing the specific visual markers of this pest’s feeding and understanding its life stages are necessary for accurate identification.
The Progressive Stages of Damage
The initial signs of squash bug activity appear as small, pale yellow or white spots, often called stippling, on the leaves. These spots result from the bug’s mouthparts penetrating the leaf surface to suck out sap, leaving behind localized areas of dead tissue. Both adults and nymphs cause this damage, which typically begins on the lower, older leaves near the base of the plant.
As feeding continues and populations increase, the damage progresses. The leaves begin to turn yellow, then bronze, and eventually become brown and brittle, appearing scorched. Heavy feeding disrupts the flow of water and nutrients within the plant’s vascular system, leading to a characteristic wilting referred to as “anasa wilt.”
This wilting usually starts with a single leaf or vine but can quickly spread to the entire plant. Small seedlings can be completely overwhelmed and killed. Larger, more established plants may lose entire runners, and affected parts, including the stems, can become blackened and crisp before the plant collapses.
Identifying the Pest: Eggs, Nymphs, and Adults
The squash bug exists in three distinct life stages on the plant. The life cycle begins with the eggs, which are small, oval, about 1/16 inch long, and shiny bronze or brick-red. They are laid in clusters, usually in neat, angled rows along the veins on the underside of leaves.
After hatching, immature nymphs emerge and go through five molting stages, changing appearance as they grow. The youngest nymphs have a light green abdomen with black legs and head, often feeding gregariously in tight clusters. As they mature, they become larger, ranging from mottled white to light gray or brownish-gray, developing black legs and antennae before forming wing pads.
The adult squash bug is a flat-backed, shield-shaped insect measuring approximately 5/8 inch long. Adults are generally dark gray or brownish-gray, with the edges of their abdomen often featuring alternating orange or gold and brown stripes. These adults are secretive, quickly scurrying to hide under leaves or debris when disturbed, and they emit a foul odor when crushed.
Ruling Out Other Common Squash Problems
The visual collapse of a squash plant can be caused by other pests, making it necessary to distinguish squash bug damage from two common issues: the Squash Vine Borer (SVB) and Bacterial Wilt. Squash bug damage is characterized by gradual leaf stippling and wilting caused by external piercing and sucking, with the insects visible on the leaves and stems.
Squash Vine Borer damage results in a sudden and complete collapse of the vine or the entire plant above the point of attack. This internal pest leaves a telltale sign of sawdust-like frass (excrement) near a visible entry hole in the stem, typically near the base of the plant. Unlike the squash bug, the SVB larvae are hidden inside the vine.
Bacterial Wilt, transmitted by the cucumber beetle, is another form of sudden wilting often confused with anasa wilt. This bacterial infection is systemic and irreversible; however, leaves may remain green even as they droop. A diagnostic test involves cutting a wilted vine and gently pulling the halves apart to check for a sticky, stringy bacterial ooze.