Borer Beetles

Identification

Size: Adult borer beetles range in size from about 1/8 inch (3 mm) to 2.5 inches (6 cm) in length.

Color: Borer beetles tend to be metallic or have a metallic sheen, with colors ranging from copper, bronze, and green to black.

Description: Borer beetles are a diverse group of insects that infest and damage trees by boring into their trunks and branches. Commonly found in Ash, Aspen, and Poplar trees, these beetles create holes ranging from 1/8 to 1 inch in diameter. The holes can be sparse or clustered, often appearing near the tree’s base or on lower branches. A telltale sign of borer beetle infestation is the presence of frass, a mixture of sawdust and insect excrement, at the tree’s base.

The life cycle of borer beetles typically begins with adult females laying eggs on the bark of host trees. Upon hatching, the larvae bore into the tree and create tunnels as they feed on the wood, disrupting the tree’s ability to transport nutrients and water. This damage can lead to tree stress, weakening, and eventually death if left untreated. Signs of borer beetle infestation include holes in the bark, often ranging from 1/8 to 1 inch in diameter, and the presence of frass, a mixture of sawdust and insect excrement, at the base of the tree.

Identifying borer beetles involves observing the adult beetles, examining the host tree, and looking for signs of infestation.

Adult beetles: Observe size, colour, and body features. Examples include the metallic green Emerald Ash Borer, the black and white-spotted Asian Longhorned Beetle, and the metallic bronze Bronze Birch Borer.
Host tree: Certain beetles prefer specific tree species. Knowing the infested tree type can narrow down possible beetle species.
Infestation signs: Look for holes in the bark, frass (sawdust and insect excrement) at the tree base, and visible tunnels under the bark. Hole size, shape, and location provide clues about the beetle species.
Larval feeding patterns: Examine tunnel shapes and patterns created by larvae. Flatheaded borer larvae create wide, flat tunnels, while roundheaded borer larvae create rounded tunnels.
Consult an expert: If unsure about the beetle species, consult an arborist, entomologist, or pest control expert for accurate identification and management strategies.
Take photos: Capture clear, detailed images of the beetle, host tree, and infestation signs to share with an expert for identification.

Some signs that may indicate a borer beetle infestation include:

Holes in the bark: Borer beetles create round or oval-shaped holes in the tree’s bark as adults emerge or when they lay eggs. Hole sizes can range from 1/8 to 1 inch in diameter.
Frass: The presence of frass, a mixture of sawdust and insect excrement, at the base of the tree or around the holes in the bark is a sign of borer beetle activity.
Visible tunnels or galleries: Borer beetle larvae create tunnels (galleries) beneath the bark as they feed on the tree’s wood or inner bark. These tunnels disrupt the tree’s nutrient and water transportation, causing stress and damage.
Branch dieback and canopy thinning: As borer beetles weaken the tree, branches may die back, and the tree’s canopy may become thin or sparse.
Bark splitting or cracks: The tunnels created by borer beetle larvae can cause the bark to split or crack, exposing the inner wood and the galleries.
Sap leakage or oozing: In response to borer beetle damage, some trees may produce sap that leaks or oozes from the holes or bark cracks.
Unusual woodpecker activity: Woodpeckers often feed on borer beetle larvae, so increased woodpecker activity on a tree could indicate an infestation.
Decline in tree health: A tree infested with borer beetles may exhibit poor health, including yellowing leaves, wilting, or overall decline.

Preventing borer beetle infestations involves a combination of proactive measures to maintain tree health and deter beetles from laying eggs. Here are some steps you can take:

Tree health: A healthy tree is more resistant to borer beetle infestations. Ensure proper watering, fertilization, and mulching to maintain tree vigor.
Prune properly: Prune branches correctly, avoiding excessive or improper cuts that can stress the tree and attract borer beetles. Remove dead, dying, or infested branches to prevent the spread of beetles.
Monitor trees: Regularly inspect your trees for signs of borer beetle infestations, such as holes in the bark, frass, or tunneling under the bark. Early detection allows for prompt intervention.
Pheromone traps: Some borer beetle species, like the Emerald Ash Borer, can be monitored using pheromone traps. These traps help detect their presence and provide information on their population levels.
Physical barriers: Wrapping tree trunks with burlap, plastic, or other materials can deter adult beetles from laying eggs on the tree bark. This is particularly useful for young or vulnerable trees.
Chemical prevention: In some cases, applying a preventative insecticide to the bark and branches of susceptible trees can help deter borer beetles. However, use insecticides judiciously and consult an expert before application.
Choose resistant species: When planting new trees, consider selecting species that are less susceptible to borer beetle infestations or are known to have greater resistance.
Remove infested trees: If a tree is severely infested or has succumbed to borer beetles, remove it promptly to prevent the beetles from spreading to nearby trees.
Sanitation: Dispose of infested wood, fallen branches, or dead trees properly, as these can serve as breeding sites for borer beetles.