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One Nation's Beetle, Another Nation's Pest: The Japanese Beetle

  • Writer: HYUN SIM
    HYUN SIM
  • Jan 7
  • 3 min read
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The Japanese Beetle (Popillia Japonica) is widely known as an invasive species. The adults measure around 15mm in length and 10mm in width (Wikipedia). Its elytra, which is the part of the shell covering the wings, is an iridescent copper. The thorax and head are metallic green. The males are slightly smaller than the females (Wikipedia).

This beetle is native to Japan hence its name but can be found in North America and Europe. The Japanese Beetle is invasive in those areas except for Japan. This species can be controlled naturally in Japan thanks to an abundance of predators (Wikipedia).

There are many methods that are used to either attack or defend against these beetles. The types of large plants that are most susceptible to this species are trees and shrubs that suffer from regular, severe foliage damage (Wisconsin Horticulture). The Japanese Beetle feeds on these damaged trees and kills them. To counter this, people ensure that their shrubs and trees are well established with proper usage of mulch and water.

For smaller plants, nylon insect screens are an effective method of combating the potential damage inflicted by this species. These screens need to have a mesh size of a quarter inch. The edges of the screen need to be secured to the ground (Wisconsin Horticulture).

Insecticides are a viable option when handling an infestation. Suggested insecticides are Chlorantraniliprole and Bacillus thuringiensis subsp. galleriae because they get the job done while having minimal impact on non-targeted inhabitants. These non-targeted inhabitants can include pollinators or predators of pests (Wisconsin Horticulture).

Anyone can use the classic method of manually knocking off the insects and placing them in soapy water to neutralize them (Wisconsin Horticulture).

To avoid infestations in the first place, turf should not be watered between July and mid-August which is the time period of greatest activity. The dry environment will discourage females from laying eggs (Wisconsin Horticulture).

The eggs are laid on the soil surface individually or in small clusters. Within two weeks the eggs will hatch into the larvae (Wikipedia).

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The larvae will feed on roots and organic material, committing its first act that labels it as a pest. As they develop, the roots they feed on increase in coarseness (Wikipedia). This increases the detrimental impact on the plants and foliage. The larvae hibernate during the winter and awaken in the spring's warmer temperatures. Within 6 weeks of waking up, the pupa stage begins (Wikipedia). After 30-45 days, the adult will emerge and feed on leaves on the ground until their wings are capable of carrying them into the air. They release pheromones that attract more adults making the infestation a rapidly developing occurrence (Wikipedia).

There is another method of controlling this pest. Science has introduced many predators and parasites to counter this rapidly growing species. The Solitary Wasp does its job by digging up the larvae of the Japanese Beetle and paralyzing them with its stinger. The wasp then proceeds to lay its own eggs that will consume the Japanese Beetle larvae upon hatching (Wikipedia). Istocheta aldrichi is a parasite that targets the adults, specifically the female. Istocheta aldrichi will lay its eggs on the female Japanese Beetle's thorax. The eggs will burrow into the female's thorax and kill it (Wikipedia).

Despite this beetle being labeled as a pest that causes mass damage to foliage and grass, its uniqueness should not be downplayed. There is a reason it grew to such a threat and there can be something learned from this. In the beetle world, it is survival of the fittest and the Japanese Beetle may be one of the top contenders without being armed with horns or spikes! That is just incredible!


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