Ambrosia Beetle Diagnostic Guide
This insect has a broad range but is of particular concern in the southern and eastern regions of the US. The term Ambrosia beetle refers to a number of species of the insect. 40 or so are native, with several destructive non-native species as well. Native beetles prefer stressed and weakened trees, while exotic species will attack both stressed and healthy trees. The Persea genus is one the host plant groups and is important both industrially and ornamentally.
Trees at Risk
Avocado, redbay, swampbay, sassafras, pondspice, pondberry, camphor tree, pecan, peach, persimmon, golden raintree, sweet gum, oak, Chinese elm, magnolia, yellowwood, and others. Many ambrosia species will preferentially attack smaller trees, orchard trees or new plantings in particular.
Signs of Damage
- Yellowing of foliage.
- Entire branches can die.
- 1” to 2” long frass tubes the thickness of pencil lead are a dead giveaway. They are rare, though; being weak they will break in wind and rain. Some species begin feeding at the bottom of the trunk while others can attack near the base of twigs and branches.
- “Sawdust” that is actually frass can accumulate at the base of the tree.
- Pencil lead-sized holes called “shotholes” at the base twigs where the beetle has exited.
- 1.4mm – 4mm dark brown to black beetle.
- Eggs and larvae are smaller than a pencil tip and are rarely seen.
Prevention is the most reliable method available. The beetle does not feed on the host tree, so systemic insecticides are not effective. Bark sprays are the only way known to prevent trees from attack.
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.
Systemic insecticides do not work because these beetles do not actually feed on the trees. Contact insecticides can be useful in managing this pest, but beetles need to be present for best control.
A Diagnostic Guide is designed to help you identify a pest issue and management solutions. Always refer to product label for all rates and approved uses. Some images courtesy forestryimages.org. Use of the images does not imply endorsement of treatments by forestryimages.org