| Native to Japan, the Japanese beetle was first introduced
into the United States in 1916. The Japanese beetle occurs in all
states east of the Mississippi River, with sporadic infestations reported
in California, Iowa, Missouri, and Nebraska. The host range of this
insect is very large, over 300 species of plants. Adult Japanese beetles
feed on and damage some field crops, ornamental plants, shrubs, and
garden plants. The larvae feed on roots of many turfgrasses, field
crops, ornamental plants, and vegetables including Kentucky bluegrass,
ryegrass, bentgrass, corn, soybeans, tomatoes, and strawberries. This
insect is generally considered an infrequent pest of soybeans due
to the defoliation it causes. Japanese beetle adults also may feed
on silks of corn plants reducing pollination and kernel set.
Description
Japanese beetle adults, approximately ½ inch in length, are
metallic green with bronze-colored elytra (wing covers). Just below
the elytra, on each side of the abdomen are six tufts of white hair.
Both the sexes of the adult beetles have the same markings, but the
males are usually smaller in size than the females. Eggs of the Japanese
beetle vary in color from translucent to creamy white. Under highmagnification,
tiny hexagonal punctures appear on the surface ofthe egg. Newly laid
eggs are about 1/20 to 1/16 inch in diameter and ellipsoidal. As the
eggs mature, they double in size, and take amore spherical shape.
The larvae, or grubs, are about 1 inch inlength. The C-shaped grubs
are creamy white with a brown head capsule. The immatures possess
chewing mouthparts and have three pair of legs onthe thorax. The grubs
are similar in appearance to other commonly found white grubs in the
soil. Japanese beetle grubs can be identified by the V-shaped pattern
of bristles on the raster. Pupae of Japanese beetles resemble the
adult, except the legs, antennae, and wings areclosely folded into
the body. As the pupal stage nears its end, the color of the pupa
changes from a pale tan color to metallic green.
Click each image for a larger
picture. |
Life
Cycle
Japanese beetles have a univoltine life cycle (one generation per
year). They overwinter as third instar larvae in the soil below the
frost line. As soil temperatures warm in the spring, the larvae move
closer to the soil surface. They complete pupation and emergence beginsin
late May and early June. Peak emergence generally occurs 4 to 5 weeksafter
initial emergence. At that time, emerging beetles crawl or fly in
search of host plants to feed and mate. Japanese beetles are naturally
gregarious and tend to aggregate on host plants.
In mid-June, female beetles begin laying eggs in the soil. During
the day, females will leave host plants, burrow into the soil, and
lay between 1 and 4 eggs at a time. Mating and egg laying occurs throughout
the entire life of the adult beetle which lasts from 30 to 60 days.
a female may lay between 40 and 60 eggs during her lifetime. Depending
ontemperature, eggs hatch in about 10 to14 days after they are laid.
Larvae complete three instars, while feeding on plant roots and decaying
plant material.
Injury
Japanese beetle adults feed on more than 300 plant varieties.
These insects exhibit a preference for some plants over others,
thus damage to preferred plants is more severe. The beetles
defoliate host plants, chewing tissue between the leaf veins,
leaving a lace-like skeleton. They generally feed on foliage
on the upper and outermost parts of the plant, working their
way down the plant. Severely injured leaves turn brown and drop
off the plant.
In corn, Japanese beetles cause injury both as grubs and adults.As
grubs, they feed on root hairs, interfering with the uptake
of water and nutrients. Injury caused by grubs will often go
unnoticed until plant growth and development is affected. Nutrient
deficiencies such as phosphorous may cause the purpling of corn
stems. Heavily infested fields may have significantly reduced
plant stands and may result in replanting. Japanese beetles
feed on corn silks as adults, interfering with thepollination
process. Extensive silk clipping may lead to incomplete ear
fill and yield loss. |
Silk clipping on corn
M. Montgomery,UI Extension
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Defoliation on soybeans
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In soybeans, grubs also feed on the root hairs of seedling plants,
though the injury is generally not of economic importance. The
main threat of Japanese beetle adults in soybeans is the defoliation
of soybean plants. Much of the defoliation of soybeans occursduring
the reproductive stages of plant development. Feeding on flowers
may interfere with pollination. Japanese beetles are part of a
complex of insects that feed on soybeans. Individually, Japanese
beetles may not cause sufficient injury to warranttreatment, but
when combined with the feeding of other soybean defoliators, treatment
may be needed occasionally. |
Scouting
Procedure
| In soybeans: It's important to scout flowering soybean
fields for the presence of the Japanese beetle and the extent
of defoliation. Estimate the number of beetles per foot of row
and examine the plants to determine if any blooms are being destroyed.
Estimate the percent defoliation in at least five different areas
of the field. Insecticidal treatments should be considered when
defoliation reaches 30% before bloom and 20% before bloom &
pod fill. |
Estimating soybean defoliation
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In corn: Estimate the number of beetles per ear and the
examine ears todetermine the extent of silk clipping. Be sure to look
at a representative portion of the field. Populations of Japanese
beetles are usually clumped together as a result of the pheromones
they emit that cause them to aggregate. There are usually clumps of
Japanese beetles near field edges, probably due to beetles moving
from areas of emergence to host plants within the area. If sampling
only occurs near areas where these clumps of Japanese beetles occur,
densities across the field may be over estimated.Even though densities
may appear to be extremely high, the average density of beetles may
be below levels of economic concern. An insecticidal treatment is
should be considered during the silking period if:
1.) there are 3 or more beetles per ear,
2.) silks have been clipped to less than ½ inch, AND
3.) pollination is less than 50% complete
*Note* When scouting for Japanese beetles, be cautious of falseJapanese
beetles. False Japanese beetles are usually found in areas with sandy
soils. False Japanese beetle rarely cause economic injury to crops,
but it is important to correctly identify them. About the same size
as Japanese beetles, false Japanese beetles are similar in appearance
to Japanese beetles, but are more dull in color whereas Japanese beetles
are shiny and more brightly colored. False Japanese beetles do not
have the characteristic arrangement of the six white tufts along their
abdomen as do Japanese beetles. Control of false Japanese beetles
is not recommended in agricultural crops in Illinois.
Management
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Japanese beetles aggregating
on corn silks
|
Management of the Japanese beetle in corn and soybeans is very
challenging. Both the adults and larvae have the potential to
cause injury to these crops in different ways. It is difficult
to predict where grubs will be present from year to year. Heavily
infested areas with grubs do not guarantee the crop planted in
that same area will suffer severe injury due to adult feeding.
Eventhough adults tend to aggregate, theyare very mobile. Therefore,
controlling one life stage will notnecessarily eliminate problems
with the other. |
| Management of adult beetles focuses on the prevention of defoliation
in soybeans and silk clipping in corn from exceeding economic
levels. Scouting entire fields is essential in determining the
extent of injury of a crop. Japanese beetle injury to either corn
or soybeans will add to other stresses that the crop is experiencing
(such as moisture stress). Consider adjusting the economic thresholds
accordingly. A reduction in economic thresholds for insect injury
when plants are suffering from other stresses may be warranted.
The potential for lower yields usually results in an increase
of economic thresholds. There are many insecticides labeled for
use oncorn and soybeans to control Japanese beetles. When making
a decision on regarding the use of an insecticide, take into account
several factors: the density of Japanese beetles, amount of injury
(silk clipping in corn, defoliation in soybeans), level of crop
stress, yield potential, and cost of control. |
Pheromone bucket trap
R. Hines, University of Illinois
|
Japanese beetle traps are most useful for detecting Japanese beetle
emergence and monitoring population fluctuations. Since the trapping
of adult beetles involves the use of pheromones, traps generally attract
beetles from surrounding areas. Their use as a tool for control is
not recommended.
Predicting future infestations of Japanese beetles would most likely
be frustrating and often futile. However, one can generally anticipate
economic densities of Japanese beetles after mild winters, followed
by early planting (the first 2 weeks of April). Infestations also
are the greatest in east-central Illinois where there is a history
of repeated problems with this insect.
More
Information
Japanese
Beetle Watch, North Central Integrated Pest Management Center.
Japanese Beetle.
Ohio State University Extension Fact Sheet.
Japanese
Beetle in Kentucky Soybean, University of Kentucky.
NAPIS
Cooperative Agricultural Pest Survey Program, Japanese Beetle. |
Authors:
Kelly A. Cook (kcook8@uiuc.edu)
Michael E. Gray (megray@uiuc.edu)
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