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University
of Rhode Island GreenShare Factsheets
Cucumber
Beetles Coleoptera:
Chrysomelidae
Both
the spotted cucumber beetle, Diabrotica undecimpunctata howardii
Barber, and the striped cucumber beetle, Acalymma vittata
(Fab.), are native insects ranging from Mexico to Canada, though
they tend to be most abundant and destructive in their southern
range. Striped and spotted cucumber beetle adults feed on foliage
and stems of young cucurbit seedlings all season long, causing reduced
stands. Adults also harbor the bacterial
wilt organism (Pseudomonas lachrymans) in the winter
and transmit it during the growing season. They also help spread
cucumber mosaic. Larvae injure plants by feeding on the roots and
tunneling through stems.
The adult spotted cucumber beetle is about 6mm (1/4 inch) long with
a bright yellowish-green body. The head, legs and antennae are black,
and 12 black spots appear on the wings. Adult striped cucumber beetles
are about 5mm (../images/16 inch) long, black and yellow in color,
and have three longitudinal black stripes on the wing covers. Both
have beaded antennae about 2 mm (1/16 inch) long. The eggs of both
cucumber beetles are oval, orange-yellow in color, and are found
in clusters of 25-50 on undersides of host leaves. The larva is
about 12 mm (1/2 inch) long with a yellow-white, somewhat wrinkled
body and six long, brownish-colored legs. Striped cucumber beetle
larvae are more flattened on the top of the abdomen. The pupa ranges
from white to yellow in color and is about 6 mm (1/4 inch) long.
Unmated
adults overwinter in neighboring woodlands under leaves and trash.
Adults leave their winter sites in late March and lay eggs from
late April to early June. Before cucurbits become available to adults,
they devour cotyledons and stems. Larvae feed in the soil on stems
and roots, become full grown in two to four weeks, and pupate in
the soil. First generation adults emerge from late June to early
July. A complete life cycle requires from six to nine weeks. There
are two and sometimes a partial third generation each year.
Cucumbers, cantaloupes, winter squash, pumpkins, gourds, summer
squash and watermelons are preferred by adult striped cucumber beetles.
They also feed on beans, peas, corn and blossoms of several wild
and cultivated plants. Larvae develop on these and related cucurbits.
The spotted cucumber beetle has a wider host range and, in addition
to cucurbits, may be found on beans, peas, potato, beet, tomato,
eggplant and cabbage. The larva is the well-known southern corn
rootworm which feeds on the roots of corn, peanuts, small grains
and many wild grasses. Adults
feed on young seedlings, causing poor stands and reduced yield.
They chew leaves and tender shoots, often girdling stems. They feed
on blossoms as well, and late in the season will gnaw holes in the
fruit. They are known carriers of bacterial wilt and vectors of
cucumber mosaic. Several cultural
measures discourage cucumber beetles. Early plowing-discing removes
vegetation and discourages egg laying. Delayed planting (more favorable
germinating conditions) and heavy seeding rates ensure a good stand.
These pests are usually not as troublesome in sandy soils. Wire
or cloth screen protectors shaped like cones or row covers will
keep beetles off of home plantings until plants are well-established.
A foliar insecticide applied at the cotyledon stage will retard
cucumber beetle feeding and encourage plant establishment. Where
insects are abundant, additional foliar applications may be needed
to prevent beetles from spreading bacterial wilt and cucumber mosaic.
Be sure to read and follow all label instructions, including intervals
between spraying and harvest. Some seed catalogs carry resistant
plants which are adequate for homeowner problems with cucumber beetles.
Adapted
from K.A. Sorensen, North Carolina Cooperative Extension Service,
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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