The Japanese Beetle Life Cycle

Japanese Beetles (Popillia japonica Newman) are a non-native invasive pest that is found in every state east of the Mississippi River. Arriving in the US on imported plants from Japan in 1916, the Japanese beetle has no natural enemies in the United States. Knowing the Japanese beetle life cycle might give you a better chance to fight these pests.

Japanese beetles are about half an inch long and have copper colored wings over a metallic green body. These beetles eat the leave of many plant species, leaving only a leaf skeleton behind. The grubs of Japanese beetles eat the roots of grass and can cause wide spread turf damage.

The Beetle Or The Egg?
Japanese beetles mature and come out of the ground in late June. Mature beetles will rest on plants low to the ground to gain strength. The early beetles will fly off to find food. Once the first beetles find suitable plants to eat, they begin emitting a congregation pheromone (scent) that attracts other beetles to the target plant.

In this part of the Japanese beetle life cycle, mating will begin as soon as females come up out of the ground. After feeding and mating, a female will burrow two to four inches back into the ground to lay one to five eggs. She will repeat the feeding, mating and egg laying cycle until she has produced between 40 and 60 eggs.

Life Underground
For 10 months of the year, the Japanese beetle life cycle takes place underground.

In evenly moist soil, Japanese beetle eggs will grow from a flat white oval into a more rounded form in a few days. Egg development will take from 30 days in cool weather to as few as 10 days in warm weather.

Larvae are produced from the eggs that will dig their way back near the surface in August. Japanese beetle larva will feed on the roots of turf grass. Beetle larva may tunnel horizontally in search of food and this some times gives the ground a spongy feel.

Around mid-October, Japanese beetle grubs will begin digging deeper underground and become dormant for the winter. The grubs will dig four to eight inches deep and sometimes deeper in harsh winters.

Spring Feeding
As the soil warms in the spring, the Japanese beetle life cycle continues as the grubs dig their way toward the surface to feed on turf grass roots. Typically, Japanese beetle grubs are active near the surface when the soil temperature reaches 60 degrees. In late May the grubs enter a pupa stage. The pupa will soon produce mature beetles that will emerge in June to begin the cycle again.

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