The larva is white, thick-bodied, legless, and 1 inch long when full grown. The adult is a red and black, wasplike moth with clear wings and tends to sit on host plants and beans in the early morning. Reddish brown eggs are laid at the base of the stem just above or below the soil line.
The larva tunnels in the stems of squash, pumpkin, and other vine crops, causing plants to wilt and die in mid- to late season.
Squash vine borers overwinter as mature larvae in small cells 1½ to 3 inches below the surface of the soil. Pupation occurs in the spring, and adult moths emerge in June and July. In southern Illinois (and similar latitudes) emergence may begin as early as May. After mating, females lay eggs at the base of plants, on stems, and on petioles. Eggs are laid singly and hatch in 10 to 15 days. Soon after hatching, larvae begin to bore into the plant. Feeding continues for about 4 weeks, and larvae pass through 4 instars before exiting the stems to drop to the ground, burrow into the soil, and pupate.
In southern Illinois, a second flight of moths will occur in late summer. In more northern areas, the larvae or pupae of the first generation will remain in the soil through the winter.
- Susceptibility varies greatly among varieties. Zucchini, blue hubbard, acorn, and delicata are very susceptible. Butternut squash is highly resistant to attack.
- When vines begin to run, scout twice weekly for the moths and for the entrance holes and frass.
- Treat as soon as early damage occurs and again five to seven days later. Then continue scouting and treat as soon as new damage is noted.