Squash Vine Borer
Ohio State
University Extension Fact Sheet HYG-2153-92
Entomology
Celeste Welty
Damage
Attack by 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, which prevents
water and nutrients from
circulating in the plant. The point where a borer
enters a stem is marked by a
hole with yellow granular or sawdust-like frass
exuding from it. 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 are
root feeding by larval cucumber
beetles, or a bacterial wilt infection.
Hosts
Squash, zucchini, pumpkins, and gourds are attcaked. The
borer prefers hubbard
squashes over other hosts. Butternut squash is less
susceptible than other
squashes. Cucumbers and melons are usually not
attacked.
Classification
Melittia cucurbitae (Harris); Order
Lepidoptera, Family Sesiidae.
Appearance
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
marked with
orangish-red, 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.
Life Cycle and Behavior
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. Moths are active during the
daytime and in the evening they
rest on leaves. This is different than the
behavior of most moths, which 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 4 to 6
weeks. Fully grown larvae leave the stems and
crawl into the soil to pupate.
There is usually one generation per year in
Ohio, but a partial or complete
second generation is possible.
Life stages of squash vine
borer; adult male (a), adult female (b), egg
(c), larva (d), earthen cell (f), pupa (g).
A trap baited with the squash vine borer's sex pheromone
would be a useful tool
in determining when the moths are active. This
pheromone has been identified but
is not yet commercially available.
Natural Enemies
The stage most susceptible to natural enemies is the egg
stage, which is
attacked by parasitic wasps. Larval and adult ground beetles
(Family Carabidae)
can attack larvae of squash vine borer, but do not appear
to cause significant
mortality.
Cultural Control
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 Control
The following are suitable in small plantings:
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 Control
Squash vine borer can be killed by chemicals but the trick is
in the timing of
the application. An insecticide is effective when applied
at the time that eggs
are hatching. A preventive treatment regime is to
apply an insecticide when
vines begin to run, and re-apply every 7 to 10
days for 3 to 5 weeks. The
application should be directed to the base of
plants, at crowns and runners.
Chemicals used for borer control in gardens are methoxychlor,
rotenone,
pyrethrum, malathion, or carbaryl (Sevin), applied as sprays or
dusts.
Restricted-use insecticides used for borer control by commercial
growers include
endosulfan (Thiodan) and pyrethroids (Ambush, Asana,
Pounce). 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.
NOTE: Disclaimer - This publication may contain pesticide
recommendations that
are subject to change at any time. These
recommendations are provided only as a
guide. It is always the pesticide
applicator's responsibility, by law, to read
and follow all current label
directions for the specific pesticide being used.
Due to constantly changing
labels and product registrations, some of the
recommendations given in this
writing may no longer be legal by the time you
read them. If any information
in these recommendations disagrees with the label,
the recommendation must
be disregarded. No endorsement is intended for products
mentioned, nor is
criticism meant for products not mentioned. The author and
Ohio State
University Extension assume no liability resulting from the use of
these
recommendations.
All educational programs conducted by Ohio State
University Extension are
available to clientele on a
nondiscriminatory basis without regard to race,
color, creed,
religion, sexual orientation, national origin, gender, age,
disability or Vietnam-era veteran status.
Keith L. Smith, Associate
Vice President for Ag. Adm. and Director, OSU
Extension.
TDD No. 800-589-8292 (Ohio only) or 614-292-1868