Japanese beetles are widely known to be one of the most destructive garden pests and one of the most difficult to eradicate. These insects feed on a variety of plants, trees and shrubs including maple trees, roses and pine trees. Not only do these insects eat the foliage of plants, the grubs feed on the roots, which can result in the death of an entire tree.
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What Are Japanese Beetles?
Japanese beetles are a type of insect belonging to the beetle family, which grow to about a half-inch long and are typically metallic green in color with copper wing covers. These insects were first discovered in the United States in 1916, somehow accidentally transported from Japan, their native habitat. Japanese beetles are extremely destructive, feeding on over 300 kinds of plants, trees and shrubs, and though a single adult beetle does little damage, they tend to feed in large groups that can destroy an entire tree.
Japanese Beetles and Pine Trees
Damage to pine trees by Japanese beetles comes from two directions. Adult Japanese beetles feed on the foliage of trees, typically working from the top of a tree downward. Because pine trees have needles rather than leaves, adult Japanese beetles do little damage to pine trees. The most damage done by these insects is actually perpetrated by the grubs laid in the soil at the base of the tree. Shortly after emerging, adult Japanese beetles lay their eggs in the soil beneath trees. As the eggs develop into grubs, the grubs begin to feed on the roots of the tree and other nearby vegetation. By damaging the roots of pine trees, Japanese beetles make the trees susceptible to further damage by wind, infection and parasites.
Damage to Other Types of Trees
Japanese beetles are particularly drawn to maple trees, roses, lindens and certain varieties of flowering crabapple. In addition to pine trees, these insects inhabit and feed on elms, poplars, birch, chestnut and walnut trees. Because these trees and plants have leaves rather than needles, adult Japanese beetles feed voraciously on the foliage, leaving them skeleton-like. While adult beetles work their way from the top to the bottom of a tree, the grubs in the soil feed on the roots of the tree and the surrounding grass, leaving wide patches of dead turf and damaged tree roots.
Japanese Beetle Control Methods
To protect your pine trees and to get rid of a population of Japanese beetles there are several things you can do. The first step in protecting your plants against Japanese beetles is to destroy the grubs that live in the soil and feed on the roots of trees. Soil insecticides and certain bacteria like Paenibacillus popilliae, also called milky spore, can be introduced into the soil to kill grubs. Traps and commercial pesticide sprays can be used to kill adult beetles that are already feeding on your plants. The best way to destroy a Japanese beetle infestation is to employ a combination of all of these methods in order to kill grubs and existing beetles.