Life history and habits

All beetles undergo complete metamorphosis, and have four life stages: egg, larva, pupa, adult. The larvae overwinter in the sapwood or heartwood of host trees. Adults typically emerge the following spring by burrowing a D-shaped exit hole through the bark. Females are fertilized within a week after emerging and live about 30 days. After mating, a single adult female will lay around 100 eggs singly or in small groups over her lifetime. Eggs are laid under or in between cracks of bark on the sun-exposed areas of trunks. Although peak egg laying occurs in late May through June, eggs can be laid any time during the growing season.

After 8-16 days, the eggs hatch and young larvae bore a hole directly through the egg into the tree bark where they feed within the host for several months. Larvae can develop more quickly and tunnel more extensively in trees with low vigor. In healthy trees, larvae are more likely to be killed by plant defense mechanisms such as the production of sap. Full grown larvae bore deeper into the tree where they overwinter and pupate in early spring. This species produces one generation per year, although some larvae require more than one year to complete their development.

Monitoring

Surveying can be done in spring with purple traps coated with an adhesive paste. This trap targets a wide range of buprestids, so accurate identification depends on knowing which pests are problematic in the area. Trees can also be assessed for injury by flatheaded appletree borer; this is best done in the early spring before adults emerge and begin reproducing. Visual indicators of infestation on the host tree include sap oozing from gaps in the bark, the presence of “galleries” under bark, dieback of twigs and branches, and the presence of D-shaped holes. Sometimes adults can be found on patches of bark exposed to the sun.

Prevention

The best strategy is to prevent infestations in the first place by keeping trees healthy. Planting new trees near flowering crab apples (Malus baccata), hawthorn (Crataegus spp.), or service berries (Amelanchier spp.), should be avoided since these serve as wild host plants for this insect pest. Farmers should consider removing wild host plants within 300 yards of the orchard. However, research suggests that the presence of weeds or cover crops may protect trees from infestation at the expense of tree growth.

Other considerations that can affect tree health include soil quality, site selection, planting practices, pruning practices, irrigation, and of mechanical injuries. When selecting sites, some factors to consider are the amount of sun exposure, wind, and whether the site is prone to late or early season frosts. Planting trees in turf should be avoided since it can compete with trees for irrigation and nutrients and is likely to contribute to damage to tree trunks during mowing. Planting new trees too deeply should be avoided, and root girdling should be prevented. More information on effective planting practices is available here. Regarding irrigation practices, a general rule is to irrigate deeply every two to four weeks by allowing the water to saturate 0.6 m (2 feet) into the soil. While the exact irrigation needs depend on the type of tree and rainfall, allowing the soil to dry moderately between watering is generally regarded as a good practice for maintaining tree health. Care should also be taken to correctly prune trees – more information on proper pruning practices is available here. Since damaged bark is attractive to egg-laying females, young trees with thin and dark bark can be wrapped with white tree wrap in late fall from the lowest limbs down to the base of the tree in late fall. This will help prevent winter sunscald, which occurs when sun-exposed bark is heated during the daytime and exposed to freezing temperatures at night. The wrap can be removed the following spring. Whitewashing can also help prevent sunscald, which involves applying a white reflective paint to trunks.

Cultural control

Heavily infested trees should be removed and destroyed by burning. Deadwood should also be removed and sanitized. The use of trap logs can help mitigate the severity of infestations. Freshly cut posts or fallen logs can be placed in the exposed sun and coated with an adhesive or left alone until after the egg laying period. Trap logs should then be removed and burned. In the spring, tree trunks can be covered up to the branches. This provides a physical barrier between pregnant females and their preferred sites on bark for egg laying. However, this method can result in unfavorable growth of sprouts when all cut surfaces are covered, giving the tree a knotted appearance.

Removing larvae by hand is a labor-intensive but effective strategy. Bark should be assessed for pinholes exuding sawdust. Using a knife, the bark in this area can be cut while using care to avoid further damage to the tree. A hooked wire can be used to impale and remove individual larvae from the tree.

Biological control

Natural enemies of flatheaded appletree borer include ants, woodpeckers, and parasitic wasps. Removing vegetation from the base of trees so the trunk is exposed helps provide these natural enemies with greater access to the pest.

Chemical control

Long-term chemical control of this pest is impractical and costly and should be used as a temporary solution in conjunction with the management practices described above. Insecticides can be applied in different ways and target different life stages of the pest. Spraying foliage with contact insecticides targets adult beetles before they have a chance to lay eggs. This should be done after adults emerge and again after three weeks for a repeat application. These insecticides can also be applied shortly after the tree’s blooming period, although this should be avoided, when possible, to minimize adverse impacts on pollinators. Lastly, intentional cuts made for grafting and bud growth should be covered with one of these contact insecticides in order to kill egg laying females.

Systemic insecticides can be applied to the soil in the early spring, fall, or after budbreak. This method targets eggs and larvae. The timing of application is important, as the toxins must be absorbed into the tree where they can act on juvenile stages. It is important to check pesticide labels before purchasing and applying.

References

Addesso, K., J. Oliver, N. Youssef, and D. Fare. 2020. Evaluation of Systemic Imidacloprid and Herbicide Treatments on Flatheaded Borer (Coleoptera: Buprestidae) Management in Field Nursery Production. Journal of Economic Entomology. 113(6): 2808-2819. Available https://academic.oup.com/jee/article/113/6/2808/5932791

Beddes, T., and M. Caron. 2014. Pacific Flatheaded Borer and Flatheaded Appletree Borer. Utah State University – Extension. Available https://extension.usu.edu/pests/uppdl/files/factsheet/flatheaded-borers.pdf

Cranshaw, W. 2016. Flatheaded Appletree Borer. High Plains Integrated Pest Management. Available https://wiki.bugwood.org/HPIPM:Flatheaded_Appletree_Borer

Mississippi State University. 2020. Flatheaded Appletree Borer, Vol. 6, No. 28. Mississippi State University Extension Service. Available http://extension.msstate.edu/newsletters/bug%E2%80%99s-eye-view/2020/flatheaded-appletree-borer-vol-6-no-28

Texas A&M University (n.d.). Managing the Flatheaded Appletree Borer. Texas A&M University: Extension Entomology. Available https://extensionentomology.tamu.edu/publications/managing-the-flatheaded-appletree-borer/

University of Tennessee. (n.d.). Flatheaded Appletree Borer (Chrysobothris femorata) and Related Species. University of Tennessee: Institute of Agriculture. Available https://www.tnstate.edu/faculty/ablalock/documents/Flatheaded%20Apple%20Tree%20Borer.pdf