The Pacific flatheaded borer (Chrysobothris mali Horn), a serious pest throughout the United States and Canada, is a dark bronze to reddish copper beetle with distinct copper spots on the elytra. . The eggs are circular and flattened whitish while the larvae vary from yellowish white to yellow. The head and thorax are almost as wide as the abdomen, forming a wedge shape. The female beetle lay their eggs on the bark, usually in sites exposed to the sun or weakened limbs. The newly emerged larvae bore through the bottom of the egg, directly into the bark. Their larval period is spent feeding in the cambium layer of the bark. Once the larva reaches maturity, it bores into the xylem and constructs an oval pupal chamber or pupates just under the bark where it stays in the prepupal stage until the following spring.
The beetle is a pest of stone fruit trees (apple, pear, peaches, apricots, cherry, plums…etc.), subtropical fruit trees such as mango and avocado as well as alder, birch, ash, ceanothus, oak, mahogany and maple.
The adult pacific flatheaded borer damage the weak, young, injured, stressed or newly transplanted trees by burrowing winding tunnels beneath the bark and girdling the trees. The larvae feed, forming long galleries (which are initially small but become larger as the larva grows) and leave behind them compressed frass. One larva can cause the death of a young tree while multiple larvae can cause the death of a strong tree. Some of the signs of pacific flatheaded borer infection are hard-packed sawdust under flaking bark, larvae beneathe the bark and oval or D-shaped emergence holes on the trees.
There are specific natural enemies for different species of beetles.
For more information contact your local BioBee field agent.