of Rhode Island GreenShare Factsheets
Colorado potato beetle, originally native to Mexico, moved into
the Great Plains, east of the Rocky Mountains, following the spread
of its Mexican host plant, buffalo burr (Solanum rostratum).
About 40 years after settlers first moved potatoes into Iowa, the
potato beetle adapted to this new host, spreading as a serious pest
of potatoes through the USA and eastern Canada since 1860, as well
as into much of Europe and Asia (interestingly, in Mexico the beetle
still ignores potatoes). The Colorado potato beetle feeds on the
leaves of several solanaceous plants and is known as a serious pest
of potato and eggplant, as well as an occasional pest of tomatoes.
Many beetle populations have developed resistance to the pesticides
that have been widely used against them.
larva of the Colorado potato beetle is a red to orange soft grub
about 1/2 inch (12 mm) long when mature. It has a black head, black
legs and, when large, two rows of black spots on each side of the
body. The larvae are often found either on the underside of leaves
or at the top of the potato plant. The adult is a distinctive yellow
and black striped beetle. Ten black stripes run along the length
of the wing covers. The beetles are convex, about 1/8 inch (8 mm)
long. The eggs, orange-yellow in color, can be found in clusters
of about 20 on the undersides of leaves.
The beetle overwinters as an adult in the soil. It emerges early
in the spring and typically walks to find new host plants. After
feeding and mating, females begin laying up to 500 eggs over a 4-5
week period. Eggs hatch in 4-9 days and larvae begin to feed immediately
upon emergence. The larvae go through 4 molts over a period of 2-3
weeks before entering the soil to pupate in a spherical cocoon.
The new adults then emerge in 5-10 days and the cycle is repeated
through a second generation.
and larvae both feed on host plants. Adult damage is generally
considered less severe, except in cases where they "stem" young
host plants early in the season. These severed plants often
die. Moderate plant
defoliation, less than about 15%, has no impact on yield, particularly
if it is early in the season. However, potato beetles are frequently
sufficiently abundant to totally defoliate plants, often killing
them prematurely and severely reducing yield.
There are several
effective means of dealing with this pest, including cultural, biological,
physical and chemical techniques, several of which work best in
Cultural techniques include the use of early plantings of fast-maturing
potato varieties that can be harvested before beetle damage becomes
significant. Crop rotation often helps delay the arrival of beetles
if new plants are kept 200 yards or so from previous hosts. Rotations
can work well with early plantings. An alternative is to delay
so that potatoes emerge after populations of overwintered adults
have declined. This approach has been proven effective when using
a heat-tolerant variety such as "Caribe." Straw mulch can also
delay beetle development, as well as enhance biological control.
Biological controls include several native insects, both predators
and parasitoids, that can be important in controlling beetle populations,
particularly later in the season. The difficulty with biological
control is that in most cases there are so many beetles early in
the season that plants are either defoliated or treated with insecticides
before the biological control agents have a chance to work. In conjunction
with cultural techniques mentioned above, the blue-green ground
beetle Lebia grandis often plays a significant role in controlling
the beetle, as do two species of predatory stink bugs, a parasitic
fly, and at least two ladybug species. A native fungus, Beauveria
bassiana, often kills high numbers of beetles late in the season,
leaving a characteristic white cadaver of beetle adults and larvae.
Restraint in pesticide use will maximize the effectiveness of these
natural biological control agents. There is also a commercially
available biological control product, Bacillus thuringiensis,
var. tenebrionis, that is effective in killing the Colorado
potato beetle. Sold under many trade names, including Novodor, Foil,
and Trident, this bacterium is most effective when used against
young larvae and should be used starting when eggs begin hatching.
Physical controls such as flaming and ditching are old approaches
that have found renewed interest among commercial potato growers
who have difficulty controlling the Colorado potato beetle by chemical
means. Homeowners can also use ditches to keep beetles from their
crops. This involves digging a ditch with steep sides lined with
sheet plastic around the perimeter of a field. Beetles walking to
crops from overwintering sites fall into the ditch and are unable
to climb or fly out. With small numbers of plants, hand-picking
of adults and egg masses can be very effective.
Chemical controls have become difficult because the Colorado
potato beetle is now resistant to most common garden insecticides
such as Sevin and diazinon. Rotenone remains effective and is commonly
used against this pest, although it also kills the beetle's natural
enemies. A botanical insecticide based upon the extracts from the
Neem tree has also been shown to be effective against the beetle.
This pesticide, which has low human toxicity, has recently been
registered for food crops.
Engineering: Genetically engineered potatoes with resistance
to the Colorado potato beetle and several other key pests are now
available to both homeowners and commercial growers. Although some
consumers are concerned about potential effects on human health,
the scientific community is more concerned about environmental effects,
including accelerated development of pesticide resistance. It is
not likely that homeowner use of genetically modified potatoes will
have adverse environmental impacts.
Dr. Richard A. Casagrande, URI Department of Plant Sciences, 1999
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.
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.
of Rhode Island Cooperative Extension provides equal program