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Asian Ambrosia Beetle
If you own a cherry tree or a Japanese Maple, be vigilant! There is an insect pest out there stalking your prized landscape tree. It is very tiny but it can bring even large trees down. The insect is a beetle and it is an illegal immigrant known as the Asian ambrosia beetle.
The Asian ambrosia beetle was accidentally imported to the United States in some peach trees in North Carolina that had arrived from China in 1974. Since then, this insect has spread all over the U.S. and has caused millions of dollars in plant loss. Every year, nursery owners spend money to prevent its damage in the southeast.
The female Asian ambrosia beetle emerges in spring from her winter habitat inside an infested tree and travels to a suitable nearby shrub or tree. She looks for a small plant or limb 1 to 2 inches thick, and begins to bore into it. She moves fast eating her way through an inch of wood per day.
As the insect eats her way through the tree, she ejects sawdust out of the entrance hole. The sawdust exiting the hole forms toothpick-like protrusions. This is the key diagnostic feature of Asian ambrosia beetle damage. Scout for this sawdust in early spring on trees and shrubs.
The insect doesn’t actually eat the wood but excavates tunnels that serve as habitat. She introduces a fungus into the tunnel, which is carried on her back from her last home. When her eggs hatch, the larvae feed on the fungus. It is this fungus that kills the tree eventually. It clogs the vascular system of the plant causing it to wilt and eventually die.
Many species of trees and shrubs are susceptible to this beetle. I have observed them attacking Tulip poplars, oaks, ornamental cherry, crape myrtle, redbud, hickory and Japanese maple. Asian ambrosia beetle will attack almost any broadleaf tree or shrub and that is a suitable size healthy or not.
Almost the entire life cycle of the insect is spent inside the plant, making the beetles hard to control with insecticides. The only time out of the tree is when it emerges in early spring to either reinfect the same tree or to seek out a new one. There are traps that can be used to monitor the insect's emergence in February.
Asian ambrosia beetles must be controlled but how? There are no systemic insecticides that will kill the beetles in the trees. Once in the tree, the beetle itself is harmless. It is the fungus that actually kills the tree. Infested trees will most likely die eventually.
The best way to control AAB damage is by prevention. Trunk sprays using pyrethroid insecticides applied in late February or when the first beetle is trapped offers protection. Products available to commercial pesticide applicators such as Pounce, Astro and Onyx all show great promise in controlling this pest. Homeowners should use outdoor tree and shrub insecticides containing imidacloprid or bifenthrin. Homeowners should remove affected plants or plant parts and they should be burned. The trunks of remaining plants should be treated with an appropriate insecticide and monitored.