Fig. 1. Adult squash bug

Fig. 2. Squash bug eggs

INTRODUCTION
The squash bug, Anasa tristis, is common throughout the United States. It primarily attacks pumpkins and squash but can also attack other curcurbits such as cucumbers. Zucchini is the least susceptible squash.

IDENTIFICATION AND LIFE CYCLE
Squash bugs overwinter as adults in sheltered places such as under plant debris, around buildings, or under rocks. Adult squash bugs (fig. 1) are somewhat flattened, 5/8 inch long and 1/3 inch wide. They are usually gray to black. The edges of their abdomens, which protrude beyond their wings, are orange or orange with brown stripes. When the adults emerge in the spring, they fly to growing cucurbit plants to feed and mate.

Female squash bugs lay eggs individually in small clusters of about a dozen either on the stems or on the undersides of the leaves between the vein angles (fig. 2). The females usually start appearing in gardens in early June. The eggs are elliptical, 1/16 in. long, and yellowish to bronze. The female continues to lay eggs through mid- summer. Eggs hatch in about 10 days or more.

The nymphs range in size from 3/16 to ½ inch in length as they progress through five stages (called instars). The young nymphs in the early instars are brightly colored with a green abdomen, a red head, and red legs. As the nymphs age, the red color turns black. The late instar nymphs are greenish gray with black legs. Nymphs require about 4-6 weeks to reach adulthood.

In the fall, especially after the vines have died, the adults, and late instar nymphs often congregate on squash fruits. The nymphs die when the temperatures drop to freezing. The adults gradually fly or crawl to sheltered places to overwinter.

DAMAGE
Squash bugs have piercing-sucking mounthparts that they use to suck the sap out of leaves. The feeding causes yellow spots that eventually turn brown. The feeding also disrupts the flow of water and nutrients, which c an cause wilting. However, unlike cucumber beetles, squash bugs do not vector diseases. Young plants are much more susceptible to damage and may die fom extensive feeding. Larger, more vigourous plants are more tolerant of feeding damage.

MANAGEMENT
The most important times to control squash bugs are when the plants are young seedlings and during flowering. Squash bugs are less important to control later in the growing season. Late season or fall feeding is not considered serious. Early detection of nymphs is important as adult squash bugs are difficult to kill. Squash bugs usually start appearing in gardens in early June. Both adults and nymphs are secretive and quickly scurry for cover when disturbed.

• Cultural Control   Maintain healthy, vigorous plant through proper fertilization and watering to help limit squash bug damage. Plant resistant varieties such as Butternut, Royal Acorn, or Sweet Cheese to help limit damage.
  
  
• Physical Control   If only a few plants are affected, handpick and kill the nymphs and adults (e.g., drop them into a pail of soapy water). Crush eggs that are attached to the stems and undersides of leaves. Another method is to trap squash bugs by laying out boards or pieces of newspaper at night; the next morning, kill any squash bugs you find. Remove plant debris around the garden during the growing season to reduce the potential harborages where squash bugs may hide. Clean up cucurbits and other plant matter around the garden in the fall to reduce the number of overwintering sites.
  
  
• Chemical Control    Insecticides are normally not required to manage squash bugs. However, if curcurbits are found wilting early in the season due to squash bug feeding, then an insecticide application may be needed to manage the insects. If large numbers of squash bugs are found in the garden later in the summer, it may be necessary to protect your curcurbits with an insecticide. It is not necessary to treat squash bugs found in the garden during late summer or fall regardless of how many are seen.

  Carbaryl (e.g., Sevin) and permethrin (e.g., Eight) are effective insecticides to manage squash bugs. The best time to apply these insecticides is during minimal bee activity, which is typically early in the morning or late at night.

CAUTION: Read all label directions very carefully before purchasing and again before using an insecticide. Information on the label should be used as the final authority. Treat only plants listed on the label of the insecticide.

This publication was modified from a Department of Entomology University Minnesota publication entitled Squash Bugs by A. Genetzky, E.C. Burkness, and W.D. Hutchison.

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