Attack by the
squash vine borer is characterized by sudden wilt of the plant.
Larvae bore within stems, usually in the lower one meter (three
feet) of the stem. Stems can be girdled by borers, preventing water
and nutrients from circulating in the plant. The point where a borer
enters a stem is marked by a hole exuding yellow granular or sawdust-like
frass. Injured vines often decay and become wet and shiny. Infested
plants may be weakened or they can die; the ultimate effect on the
plant depends on the number of borers and their location. Over 100
larvae have been found in a single plant. If a plant wilts but there
is no evidence of borers, other possible causes include root feeding
by larval cucumber beetles and bacterial
pumpkins and gourds are attacked by the squash vine borer. Hubbard
squash is preferred over other hosts; butternut squash tends to
be less susceptible than others. Cucumbers and melons are usually
Eggs are oval,
flattened, dull-red in color, and 1 mm (1/25 inch) in diameter.
The larva is a fat, grub-like caterpillar with a white wrinkled
body and a brown head. A fully-grown larva is 25 mm (1 inch) long.
The pupa is brown and 16 mm (5/8 inch) long, and contained inside
a cocoon that is made of earth-covered black silk and is 19 mm (3/4
vine borer larva.
Photo from the University of Connecticut Cooperative Extension.
The adult is
a moth that looks like a wasp; the body is black with orangish-red
markings, and the hind legs are feathery with black and orange hairs.
The front wings are metallic green, and the hind wings are transparent;
the wingspan is 25 to 37 mm (1 to 1.5 inch). Male and female moths
are similar, although the male is more colorful, smaller, has a
narrower abdomen, and more feathery antennae.
vine borer overwinters as a fully-grown larva in cocoons in the
soil, 2 to 15 cm (1 to 6 inches) deep. It pupates in the spring
and the adult (a moth) emerges in June. These moths are distinct
in that they are active during the daytime, resting on leaves in
the evening; most moths are active at night. The moths fly slowly
in zig-zags around plants and lay eggs singly on stems; eggs are
usually found on the main stem near the base, but are also found
on leafstalks or on the undersides of leaves. Moths are active for
about one month. Eggs hatch in 9 to 14 days. Larvae enter the stem
at the plant base within a few hours after hatching from the eggs.
Larvae feed inside the stem for four to six weeks. Fully-grown larvae
leave the stems and crawl into the soil to pupate. There is usually
one generation per year, but a partial or complete second generation
vine borer is most susceptible to natural enemies in the egg stage.
The eggs are commonly attacked by parasitic wasps. Larval and adult
ground beetles can attack the larvae of the squash vine borer, but
do not appear to cause significant mortality.
vines soon after harvest to destroy any larvae still inside stems.
or plow the soil in fall or spring to destroy overwintering cocoons.
vines at leaf joints with moist soil, to promote formation of secondary
roots that will support the plant if the main root and stem are
crop of very early-planted Hubbard squash can be used to alleviate
pest pressure from other cucurbits.
For small gardens:
Borers can be removed from vines if detected before much damage
is done. Examine stems in early summer; once holes are detected,
slit the stem longitudinally with a fine sharp knife, remove the
borer, then cover the wounded stem with moist soil above the point
of injury to promote additional root formation.
can be covered with a barrier, such as strips of nylon stockings,
to prevent egg laying.
and destroy the moths, especially at twilight or in early morning
when they are resting on the upper side of leaf bases.
the eggs before they hatch.
The squash vine borer can be killed by chemicals, but appropriate
timing is crucial. An insecticide is effective when applied as eggs
are hatching. A preventive treatment regime consists of applying
an insecticide when vines begin to run, and re-applying every seven
to ten days for three to five weeks. The application should be directed
to the base of plants, at crowns and runners. Chemicals used for
borer control in gardens include pyrethrum, malathion or carbaryl
(Sevin), applied as sprays or dusts. The biological insecticide
B.t., in the forms currently available, is not effective because
it cannot be applied to the plant parts that are eaten by the borer.
from the Ohio State University Extension, 1999