Insect spotlight: Ambrosia Beetles

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By Laurie Reid

City of Charlotte Assistant City Arborist

Now that spring has sprung, a lot of insects are on the move.  One group of insects that tree huggers should be on the look out for are ambrosia beetles. These little fungus farmers use trees to make their homes, but they do not eat the wood – they eat fungus!

These beetles carry fungal spores on their bodies or in specialized pouches located under their wings, on their legs, or near their mouths.  They chew into the tree and create tunnels (called galleries) for the fungus to grow and for the female beetles to lay eggs.  As the fungus grows, it blocks the water and nutrient movement in the tree, causing leaves to wilt and the tree to die. If the tree is dying, ambrosia beetles will be one of many organisms that help to aid in quicker wood recycling.

Ambrosia beetles are small (some are as small as two millimeters!), so we may not see them.  The grubs and the adult beetles only eat fungus, so the beetles keep the galleries clear of chewed up wood and poop (called frass) by pushing it out of the tree.  Be on the look out for small protrusions of sawdust (called toothpicks or noodles) sticking out of holes on the tree trunk that are the size of the lead of a mechanical or #2 pencil, or piles of fine, flour-like sawdust at the base of a tree.

There are hundreds of ambrosia beetle species in the southeastern US; some attack dying trees and some attack living but stressed trees.  When trees are stressed or dying, they release ethylene, which attracts ambrosia beetles.  Tree that are overwatered, suffer from drought stress or are injured/topped/planted incorrectly are prone to attack by ambrosia beetles. Keeping your tree healthy through proper planting techniques, watering, mulching, and protecting them from injury is the best way to prevent them from being attacked by insects and diseases.  If you suspect your tree has been attacked by ambrosia beetles, contact an arborist for an evaluation.

For more information, please visit: https://content.ces.ncsu.edu/granulate-asian-ambrosia-beetle-1

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