Flatheaded Appletree Borer

The Flatheaded Appletree Borer (Chrysobothris femorata) is a wood-boring beetle that belongs to the family Buprestidae. While its name suggests it primarily targets apple trees, it is an opportunistic pest that can infest a wide range of deciduous trees.

Host Plants

Despite its name, the Flatheaded Appletree Borer (Chrysobothris femorata) is not limited to apple trees. This pest has a broad host range and can infest various deciduous trees and shrubs. Some of the host plants commonly affected include:

• Apple trees (Malus spp.)
• Ash (Fraxinus spp.)
• Cherry trees (Prunus avium)
• Chestnut trees (Castanea spp.)
• Dogwood trees (Cornus spp.)
• Elm trees (Ulmus spp.)
• Maple (Acer spp.)
• Oak trees (Quercus spp.)
• Peach trees (Prunus persica)
• Pear trees (Pyrus spp.)
• Plum trees (Prunus domestic)
• Poplar trees (Populus spp.)
• Quince trees (Cydonia oblonga)
• Willow trees (Salix spp.)

The Flatheaded Appletree Borer may also infest ornamental and landscape plants, including some varieties of roses and woody shrubs. The range of host plants increases the borer’s opportunity to find suitable habitats, making it a pest of concern for a wide variety of landscapes.

Regions impacted

This borer is commonly found throughout most of Canada and the United States.

Description

Adult beetles are metallic, shiny gray to brown, and approximately 12 to 18 mm long. They have a flattened body and a somewhat elongated shape. The larvae are quite distinctive; they are legless and have a cream to white body with a broad, flat head, which gives the insect its name. The larvae’s flattened anterior region allows them to carve out shallow tunnels beneath the bark of host trees, causing damage to the wood and overall tree health.

Life Cycle

The life cycle of the Flatheaded Appletree Borer is a yearly cycle that encompasses four distinct stages: egg, larva, pupa, and adult.

Egg: The adult female beetle lays orange to reddish brown eggs in the crevices and cracks of tree bark, usually targeting weakened or stressed trees. Egg-laying generally occurs from late spring to early summer.

Larva: After hatching, the larva immediately begins to tunnel into the tree. It feeds on the cambial tissue between the bark and the wood, creating shallow, winding galleries filled with frass (a mixture of wood debris and excrement). The larval stage can last from several months to more than a year, depending on environmental conditions. It is during this phase that the most significant damage to the host tree occurs.

Pupa: When the larva has fully developed, it carves out a pupal chamber close to the surface of the bark. Inside this chamber, the larva transforms into a pupa. This stage generally takes place in late winter to early spring and lasts for a few weeks.

Adult: The adult emerges from the pupal chamber by chewing its way out of the bark, typically in late spring or early summer. The adults are relatively short-lived, surviving long enough to mate and lay eggs, thereby completing the life cycle.

This borer prefers weakened or stressed trees, meaning healthy trees are less likely to suffer severe infestations. However, if left unchecked, the flatheaded appletree borer can cause substantial damage, weakening trees and making them more susceptible to disease and other pests.

Damage and Detection

Damage

The Flatheaded Appletree Borer inflicts most of its damage during the larval stage. Larvae tunnel through the cambium layer, feeding on the nutrient-rich tissues between the bark and wood. These tunnels disrupt the tree’s ability to transport nutrients and water, thereby weakening it significantly. Over time, these feeding galleries can girdle a tree, potentially leading to its death.

The damage is often most apparent at the base of the trunk but can occur higher up as well. Sunken, discolored patches on the bark or oozing sap may also indicate an infestation. The holes created when adults emerge are another visible sign, usually about 1/8 to 1/4 inch in diameter. Severely infested trees may display general symptoms of decline like branch dieback, stunted growth, or increased susceptibility to diseases.

Detection

Early detection is crucial for effective management. Here are some methods to detect an infestation:

• Visual Inspection: Look for signs of damage on the bark, including cracks, small holes, or sunken areas. Fresh frass may also be visible near the entry/exit holes.
• Bark Tapping: Gently tap the bark with a mallet; a hollow sound may indicate a borer infestation below.
• Traps: Pheromone or bait traps can be used to capture adult borers, helping to confirm their presence.

Prevention and Control

Controlling the Flatheaded Appletree Borer requires a multi-pronged approach that includes cultural, mechanical, and chemical methods. Here are some strategies:

Cultural Methods

• Plant Health: Ensure your trees are healthy, as stressed trees are more susceptible. Water and fertilize appropriately. Prevention of wounds, sun scald, or drought stress can greatly reduce borer attacks.
• Weeding: Maintaining a clear area around the base of trees facilitates the detection and removal of borers and makes them more susceptible to their natural enemies. These include ants, various predatory insects, parasitic wasps, flies, as well as woodpeckers.
• Mulching: Apply mulch around the base of the tree but avoid contact with the trunk. This helps maintain soil moisture and temperature, reducing stress on the tree.
• Sanitation: Remove dead or dying branches and trees, as these can serve as breeding grounds.

Mechanical Methods

• Tree Wraps: In early spring, you can safeguard tree trunks by wrapping them up to the branch level to deter female flatheaded appletree borers from laying eggs. Utilize materials like mosquito netting, fine wire mesh, tree wrap, tar paper, cotton padding, or even multiple sheets of newspaper. Unwrap the barriers in the fall once the egg-laying season has concluded.
• Surface Deterrents: To further prevent egg-laying by female borers, consider brushing an inhibitory coating onto uninfested parts of the tree trunk. A thick paste made of insecticidal soap and caustic potash (lye) is advised. Depending on the amount of rainfall, reapply this mixture every two to four weeks from spring to late summer to discourage egg deposition.
• Sunscald Protection: Where sunscald injuries are likely, shade the lower trunk of young trees or use tree wrap to prevent this injury.
• Whitewashing: Whitewashing the trunks can also reduce attacks.
• Physical Removal: If the population is small, larvae can be killed by poking a wire into their galleries. This is often impractical for larger infestations.

Chemical Methods

• Insecticides: Insecticides can be applied to the tree’s trunk and branches. The timing of these treatments should align with the periods when eggs are being laid and hatching. Follow label directions precisely.

Professional Help

• Consult an Arborist: If the infestation is severe or if the tree has high value, professional treatment may be warranted.

Monitoring

Regularly inspect your trees for signs of borer activity. This could include:

• Sawdust-like frass: Found near entry holes or at the base of the tree.
• Cracked or sunken areas on the bark: This often indicates the galleries below.
• Branch dieback: Advanced infestations can cause this.

Prevention is always the best control method, so keep your trees healthy, monitor them regularly, and apply treatments as necessary.