Bark beetle and shot hole borer are general terms used for a large group of small beetles that chew round holes, usually in dead or dying trees and woody ornamentals. These insects inhabit the phloem layer or where bark and sapwood meet. They create characteristic tunnels or galleries in the wood, which disrupt water and nutrient flow.
Ambrosia beetles are different in several respects.
- They bore deep into sapwood.
- Females carry fungal spores with them that germinate within the tree, providing food for larvae and adults.
- While most species attack stressed or dying plants; a few enter apparently healthy ones. This combination presents significant problems. A good example is Asian (granulate) ambrosia beetle, which can live in over 200 species of trees and shrubs.
- Preventive bark sprays with insecticides are not particularly effective in preventing infestations.
- Heavily infested trees/shrubs should be removed and destroyed.
- A sound plant health program that includes practices such as optimum fertility, reduction of environmental stress when practical, and watering as needed, will help to reduce problems with borers.
By Lee Townsend, Extension Entomologist