Historically, the roundheaded apple tree borer was a significant pest of fruit trees and orchard crops. However, most recently, it has become a more significant pest of certain ornamental plants, including those in the host list above. This insect is found throughout the Northeast. As with most wood boring beetles, the larvae (immatures) do the most feeding damage, whereas the adults do very little - with only a comparatively small amount of feeding conducted on the fruit, bark, and foliage of the trees. The life cycle of the roundheaded apple tree borer takes 2-3 years to complete. Once the adult beetle is ready to emerge from the host plant, this happens by approximately June during the growing season. Adult females are capable of living for roughly 40 days, using this time to lay their eggs. Eggs are often laid during the night in young, healthy trees, at or near the ground. Eggs are 3-4 mm long, a light cream color which eventually turns a rusty brown color as they develop. The adult female creates a slit in the bark of the host plant, roughly 1/2 long, into which she inserts an egg between the bark and the xylem. On average, approximately 40 eggs can be laid per female (Becker, 1918). Eggs hatch, and the newly hatched larvae are 3-4 mm long and bore into the sapwood where they feed. Depending on the time of year, the larvae move upward and downward in the trunk as they feed. During this time of feeding, their tunnels (galleries) are enlarged which causes the most damage to the host. In the spring of the third year of development, the larva prepares to pupate in a chamber it creates approximately 1/2 inch beneath the bark before emerging as an adult by June. Adults are approximately 3/4 inch in length with white and dark brown striped bodies (3 broad, longitudinal brown stripes) with long antennae and may be seen June through August. Adults typically only fly short distances. Fully developed larvae can be up to 1-1.25 inches long, cream-colored, legless, with dark colored mouthparts. Larvae may pass through 6 instars. Historically, it was common to find 6-10 individual borers in a single tree (Becker, 1918). The roundheaded apple tree borer is an example of a native North American insect that has been introduced as an invasive elsewhere (ex. 2008 in Europe in Germany) (Kehlenbeck et al., 2009).
Foliage of host plants stressed by this insect may become yellowed, sparse, or pale. Reddish-brown colored frass (sawdust like excrement) may be found at the base of infested host plants. Look for 1/4 inch holes in the bark at the base of the trunk. Branch dieback may occur as the infestation progresses. Large tunnels occur in the sapwood. Darkened areas on the bark may be present due to sap flow. One or two borers can kill a young tree. The roundheaded apple tree borer may feed on both healthy and stressed trees. May be more of a problem in ornamental hosts than in orchard production. Neglected backyard apple trees may be severely impacted. Trees damaged by this insect may be more prone to wind breakage. Borers create most of their damage on the trunk of the tree, near the ground, within roughly 6 inches above and 4 inches below the soil. They may be found in the suckers or exposed roots of older trees. Trees 3-10 years of age are most often impacted (Becker, 1918).
Adult emergence occurs by June, with egg laying continuing through August. Visually scouting for adults may be difficult because activity occurs at night. Monitor susceptible hosts for signs of damage from newly hatched larvae near the base of the tree. Look for darkened areas stained with sap flow. If found, conduct the "worming" procedures described in the cultural management section. Look for reddish-brown sawdust-like frass that has been expelled by larger larvae through the bark of the tree and may pile up at the base of the trunk or ground nearby.
In August and September, it is possible to find where young larvae are beginning to feed by looking for sap staining on the surface of the bark. At the point of the staining, use a sharp knife to slice a shallow line vertically in the bark. This may be effective at killing the young larva, without seriously damaging the tree. At the same time of year, second year borers can be found by probing a flexibly wire (such as bailing wire) into an exposed tunnel to kill the slightly older larva. This cultural management, sometimes called "worming", can be done each year to prevent damage on individual trees. Removing weeds from the base of the trunk of host trees, as well as covering the base of the trunk with mosquito netting at the time of egg laying, are additional methods of discouraging borer activity that have been suggested.
Golden and downy woodpeckers are predators of the roundheaded apple tree borer and do at times have an impact on their populations. Information about insect natural enemies, including parasitoids, is greatly lacking in the scientific literature. An undetermined species of Carabid beetle may prey on the roundheaded apple tree borer larvae (Felt and Joutel, 1904) and Cenocoelius populator (Braconidae) was reared from beetles caught in Indiana (Riley and Howard, 1890).
Acetamiprid (L)
Beauveria bassiana (NL)
Bifenthrin (NL)
Chlorpyrifos (N)
Cyantraniliprole (NL)
Emamectin benzoate (L)
Flonicamid+cyclaniliprole (N)
Tau-fluvalinate (NL)
Imidacloprid (L)
Neem oil (NL)
Permethrin (L)
Spinosad (NL)
Active ingredients that may be applied systemically include: acetamiprid (injection), azadirachtin (injection, soil drench), cyantraniliprole (soil drench, soil injection), emamectin benzoate (injection), imidacloprid (soil drench), and neem oil (soil drench).
When used in a nursery setting, chlorpyrifos is for quarantine use only.
Make insecticide applications after bloom to protect pollinators. Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.
Note: Beginning July 1, 2022, neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.
