Ambrosia beetles are tiny dark brown to black beetles, 1.4 - 4mm, which bore through the bark and into the sapwood of many of our local trees, such as beech, oak, sweet gum and magnolia. They are highly specialized and feed on fungi that they cultivate on the tunnel walls. Both the larvae and adults feed on the fungus. Some species begin feeding at the bottom of the trunk while others can attack near the base of twigs and branches. 1"to 2” long frass tubes the thickness of pencil lead are a dead giveaway. Being weak, they don't tend to last long before breaking off in the wind and rain. In cases of severe infestation sawdust, which is actually frass, will be found at the base of the tree.
These beetles work symbiotically with fungi such as Fusarium species and Ambrosiella species. The fungi that are consumed (sometimes referred to as “Ambrosia”) are grown in galleries created by the beetles. These fungi may be responsible for the death of the tree, though the beetles introduce multiple fungi species. Prevention is the most reliable method of treatment. The beetle does not feed on the host tree, so systemic insecticides are not effective. Basal bark sprays are the only way known to prevent trees from attack. Contact insecticides can be useful in managing this pest, but beetles need to be present for best control. Maintaining tree vigor can help. Most native species will not attack healthy trees, but attack weakened, dying, or dead trees with enough wood moisture to support their symbiotic fungal growth. Some exotic species will attack both weakened and healthy trees. Cultural practices such as watering and mulching are also helpful.
Contact Plant Health Solutions for proper diagnosis and development of a treatment plan.