Jim Jasinski, Ohio State University Extension, Bugwood.org
The squash borer usually occurs in low numbers although their presence is usually not noticed until after damage is done.
Squash vine borer eggs are about the size of a pencil point, brown and flattened. Larvae have a brown head, white body and are rarely found outside of the vine. The larvae have 8 pairs of appendages from their body. The first 3 pairs are true legs, the second 5 pair are prolegs or extensions from the body wall. Each proleg has 2 rows of curved spines. Pupae are about 2 centimeters long, silk lined, black and usually found in the soil. The adult squash borer may be mistaken for a wasp. The front wings are a metallic green and the rear wings are transparent with black or brown margins and veins. Wingspan is approximately 2.5 - 4 cm. The body is orange and black, often in a ringed pattern surrounding the abdomen.
The squash vine borer overwinters as a pupa. In Pennsylvania adults emerge in mid-to-late June. Moths will oviposit throughout July and August. Eggs are oviposited singularly or in small groups on the stem immediately above the ground surface. Eggs take a week to 10 days to hatch. Larvae enter the stem immediately, leaving a small hole surrounded by frass as the point of entry. The larvae will feed on the plant for approximately 4 weeks by continuing to tunnel through the stem of the plant. When they are ready to pupate the larvae will burrow into the soil and spin a cocoon. In Pennsylvania the squash vine borer will only have one generation a year. In many southern states two generations are common.
The squash vine borer injures plants by tunneling through their stem, which interferes with nutrient transfer in the plant. Borer feeding weakens plants providing the opportunity for secondary infection. Plants damaged by the squash vine borer will wilt. Examination often reveals shiny green-to yellow colored frass within the stem. Often frass will protrude from any damaged areas of the stem. If vine senescence occurs early, the borer may tunnel into the fruit.
Not all fields will have problems with squash vine borer. Fields that have been attacked in the past are most likely to have squash vine borer problems in the future.
When infestations of squash borer are caught early it is often possible to save the plant. Where squash borer entry holes are detected, split the vine lengthwise and remove any observed borers. Entry holes are frequently just above where the vine breaks the soil. Use caution not to split any farther than is necessary to remove the insects. After careful inspection and removal of insects, place a few centimeters of moist soil over the split vine.
Proper cultural control may kill many overwintering pupae reducing the following year's population. Soil should be disked after harvest then plowed the following spring. This combination produces mortality from both the cold and from difficulties escaping from the soil. Another cultural control is to destroy vines after harvest. This prevents borers still in the larval stage from completing their development.
As with all boring insects, sprays need to be timed to contact the insects before they bore into the plant. For this reason sprays on a weekly basis are not recommended.