Popillia japonica (soybean)
Authors: Buyung Hadi, Jeffrey Bradshaw and Ken Ostlie
As the name implies, the Japanese beetle, Popillia japonica, is native to Japan. The beetle was introduced into the United States in 1916. First detected in New Jersey, the Japanese beetle currently occurs in all states east of the Mississippi river. The beetle is a generalist, capable to feed on over 300 plants including various ornamentals, grasses and row crops.
The adult Japanese beetle, the damaging stage on soybean, has metallic green or greenish head and thorax. The wing covers are shiny copper brown. Few spots of white hair tufts are visible near the end tip of the abdomen. Adult Japanese beetle is sometimes confused with false Japanese beetle, Stigoderma arbicola. Adult false Japanese beetle has dull green or greenish head and thorax with brown wing covers. The white hair tufts are absent in adult false Japanese beetle.
The larvae of Japanese beetle are C-shaped, white to cream colored grubs between 0.5 to 1.2 inches (12.7-30.5 mm) long depending on the developmental stage.
Life Cycle and Seasonal History
The japanese beetle survives the winter as third instar white grub about 5 inches (13 cm) under the soil surface. The grubs typically infest grassy areas, but some may be found within soybean fields. As the soil temperatures increase in the spring, the white grub move closer to soil surface, where it pupate within an earthen cell. The adults emerge from the soil in late May and early June. Peak emergence usually happen around 4 to 5 weeks after the initial emergence. The adults readily feed on the foliage of nearby host plants. The Japanese beetle are naturally gregarious and, thus, often seen feeding in groups. Soybean are exposed to Japanese beetle feeding from June through early September, with the highest defoliation rate occurring in July and August.
Mated females of adult Japanese beetle start to lay their eggs in mid June. To lay their eggs, females leave the host plants during the day, burrow into the soil and deposit 1 to 4 eggs at a time anywhere between 0.5 to 1.2 inches (12.7 - 30.5 mm) in the soil. A female lay 40-60 eggs during its lifetime. It takes an egg about two weeks to hatch. The larvae feed on host plant roots.
In most places in the United States, the Japanese beetle produce one generation per year. It is possible that two years are needed to complete the cycle for one generation during excessively cold weather in the northernmost part of the country.
Plant Injury and Damage
The white grubs of Japanese beetle may feed on soybean roots, but they are not considered as economically damaging pest. The adult beetle feed on the soft tissue of soybean leaves, leaving the leaf veins intact, producing a lacy appearance on defoliated leaves. The economic impact of injuries due to Japanese beetle feeding should be considered together with injuries inflicted by other defoliating pests of soybean (e.g. green cloverworm, grasshoppers, Mexican bean beetles and bean leaf beetles).
Scouting and Threshold
Feeding by the Japanese beetle alone rarely warrant management action. Considered together with other defoliating pests, management action is warranted if defoliation reaches 40% in pre-bloom, 20% during bloom and pod-fill and 35% from pod-fill to harvest.
Other Online Resources
For information regarding labels of chemical control options, please visit Agrian.com