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Life Cycle of a Japanese Beetle

Priya Johnson Sep 30, 2018
A Japanese beetle's life cycle comprises the egg, grub, pupa and adult stage. The grub stage can further be sub-divided into three instar stages and is the longest of all stages in the life of a Japanese beetle.
The Japanese beetle (Popillia japonica Newman) is one of the most abundant pests in Ohio. Introduced for the first time to the United States in 1916, this beetle is one of the most destructive and devastating pests any region can have.
They devour lawns, golf courses and gardens, thus, reducing beautiful green landscapes to barren land. The larvae of this beetle feed on the roots of grasses, while the adults feed on leaves and fruits of plants. Together they leave no signs of greenery in the area. However, these beetles, like other insects, have an interesting life cycle.


Around mid-summer, adult beetles come out and begin mating. The female after mating moves away from the plant site by noon time. She goes and burrows her way into moist, grassy soil (mostly golf courses, lawns, etc.).
Once she has burrowed herself 2-3 inches in the soil, she lays her eggs (1-5 eggs) there. The female Japanese beetle life span is about 30-45 days, during which she can lay about 40-60 eggs.


The eggs hatch within the next 8-14 days and tiny grubs emerge out. This is called the first-instar larvae. The mid-summer rainfall keeps the newly-hatched grubs from drying out. These grubs feed on the roots of turf grasses and vegetable seedlings. Within the next 20 days, the first instar larvae molts to form the second instar larvae.
These second instars take another 20-45 days to feed and mature, after which they molt again to give way to the third instar larvae. By late August, the C-shaped grubs appear completely grown. These grubs live deep in the soil, which is why gardeners find it really difficult to get hold of them.
In this grub stage, the beetles overcome the winter months. As the temperature lowers in October, they dig deeper in the soil. Some even go as deep as 10 inches, when the temperature reaches 60°F. However, if the temperature goes below 50°F, they become inactive.


In spring (mid-April), when the temperature rises and the soil warms up, these grubs come out of their deep burrows and begin feeding on the roots of grasses. After feeding thoroughly for the next 4-5 weeks, the grubs enter the pupa stage in an earthen cell 1-3 inches in the soil. They remain in the soil until they finally emerge as adults.


Adult Japanese beetles emerge during the last week of June or in July. As soon as they emerge, these beetles begin looking around for luscious, green plants and fruits to devour. Now this is where its life facts gets annoying.
These adult beetles wipe out all greens from the vicinity. All the lovely flowers, fruits and plants, no matter how exotic they are, get wiped off! Tiny as they are, they are worse than vacuum cleaners.
Besides eating, these green cleaners release aggregation pheromone to attract newly emerged females. They mate and the female goes off to lay her eggs. These adults live for 30-45 days and then die off. The entire life span, right from egg stage to adult stage is about one year.
No matter how interesting the Japanese beetle's life cycle is, the devastation caused by them causes one to wish they didn't live as long as they do. Even if they did, it makes one wish they didn't eat as much as they do. If your garden is plagued by these nasty insects try some Japanese control measures, which will help get rid of them.