Pest Information
Japanese Beetle
Popillia japonica Newman
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.
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.
Defoliation on soybeans
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
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
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.
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.
