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University
of Rhode Island GreenShare Factsheets
Squash
Vine Borer
Melittia cucurbitae
Lepidoptera: Sesiidae
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
wilt infection.
Squash, zucchini, 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 not attacked.
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 inch) long.
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.
The squash 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 is possible.
The squash 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.
• Destroy vines soon after
harvest to destroy any larvae still inside stems.
• Disk or plow the soil in
fall or spring to destroy overwintering cocoons.
• Cover 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 injured.
• A trap crop of very early-planted
Hubbard squash can be used to alleviate pest pressure from
other cucurbits.
Physical:
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.
• Stems can be covered with
a barrier, such as strips of nylon stockings, to prevent
egg laying.
• Catch and destroy the moths,
especially at twilight or in early morning when they are
resting on the upper side
of leaf bases.
• Hand-pick the eggs before
they hatch.
Chemical: 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.
Adapted from the Ohio State
University Extension, 1999
Pesticides
are poisonous! Read and follow all safety precautions on labels.
Handle carefully and store in original containers out of reach
of children, pets or livestock. Dispose of empty containers
immediately, in a safe manner and place. Pesticides should never
be stored with foods or in areas where people eat.
When trade names are used for identification, no product endorsement
is implied, nor is discrimination intended against similar materials.
Be sure that the pesticide you intend to use is registered for
the state of use.
The user of this information assumes all risk for personal injury
or property damage.
For more
information, call the URI CE Gardening and Food Safety Hotline
at 1-800-448-1011 or (401)874-2929 from outside Rhode Island;
Monday-Thursday between 9 am and 2 pm.
University
of Rhode Island Cooperative Extension provides equal program
opportunities.
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