Boring Insects

Identification And Treatment For Insects That Tunnel And Feed Under The Bark Of Trees

Many insects have the potential to devastate a single specimen tree or whole stands of trees. However, insects that bore into a tree to feed on living wood tissue are at the top of the list. Almost all trees and shrubs are subject to attack from boring insects. Healthy trees can fend off initial attacks by forming callus tissue or by creating toxic compounds that will kill young insect larvae. Trees that are under some form of environmental stress are more attractive to attack and are less able to respond defensively.

Most damage by borers is caused by the larvae or immature stage of the insect. In Minnesota the primary borer pests are the larvae of beetles and moths. Eggs are typically laid in bark crevices, branch junctions or near wounds. When the eggs hatch the small larvae chew their way through the bark to the point where the wood and bark meet. This section of wood contains the living nutritious tissues on which most borer larvae feed. These tissues, called xylem and phloem, serve as the trees’ transport system to move water and nutrients up from the roots to the leaves, and sugars from the leaves down to the roots.

When these tissues are damaged by borers the tree loses it’s ability to transport and also reduces it’s ability to respond to the borer. It is incredibly important to keep a trees’ vigor up to reduce both its attractiveness and it’s susceptibility to borers. In many cases, borers also carry diseases, such as Dutch Elm Disease that can infect the tissues in the tree and increase the rate of decline.

Flat Headed Borers

Two-Lined Chestnut Borer (Agrilus bilineatus) Attacks all oak species, prefers red and pin oak. Avoid drought stress and root damage.	Emerald Ash Borer (Agrilus planipennis) Attacks all ash species. Healthy trees are also attacked. Not in Minnesota yet... [more info]
Bronze Birch Borer (Agrilus anxious) Attacks all birch species. European and Asian hybrids are very susceptible, the North American hybrids are more resistant.	Flatheaded Apple Tree Borer (Chrysobothris femorata) Attacks many deciduous trees including apple, beech, dogwood, elm, linden, maple, oak, and willow.

 

Round Headed Borers

Pine Sawyer Beetle (Monochamus spp.) Attacks mainly non-native pine species such as Austrian, Scotch and Japanese red and black pines. Native species are less susceptible.	Red-Headed Ash Borer (Neoclytus acuminatus) Attacks all species of dying or stressed hard woods. Especially attracted to oak, ash, hickory and hackberry.
Asian Long-Horned Beetle (Anoplophora glabripennis) Attacks all hardwood trees, prefers maples, willow, poplar and elm. Not present in Minnesota, yet...	Linden Borer (Saperda vestita) Attacks linden, basswood and poplar. Attracted to stressed or healthy trees whether mature or young.

 

Wood Boring Moths

Zimmerman Pine Moth (Dioryctria Zimmermani) Attacks all pines except white pines, prefers Austrian and Scotch pines.	Dogwood Borer (Synanthedon scitula) Attacks dogwood, elm, hickory, pecan and willow.
Peach Tree Borers (Synanthedon exitiosa & Synanthedon pictipes) Attacks peach, plum, cherry, apricot, and other stone fruit trees.	Ash Borers (Podosesia syringae & Podosesia aureocincta) Attacks mainly ash and lilac

 

Bark Beetles

Pine Bark Beetles (multiple species found in our area) Attacks all species of pine. May affect other conifers as well. Attracted to stressed trees.	Spruce Bark Beetles (multiple species affect our area) Attacks all species of spruce. Attracted to stressed trees.
Smaller Oak Bark Beetle (Pseudopituophthorus minutissimus) Attacks all oak species. White oaks are more resistant. The adult oak bark beetle contributes to the transmission of oak wilt.	Elm Bark Beetles (Scolytus multistriatus, Hylurgopinus rufipes) Attacks all elms. The American elm is particularly susceptible. Carrier of Dutch elm disease.

 

Borer Management

Unfortunately, most borer infestations go unnoticed until external signs of damage begin. Damage is not usually visible until after at least one year of infestation, when exit holes of the adult are seen in bark and when dieback occurs in the tree due to the disruption of the transport system. At this point a tree needs help to recover from the damage.

Two approaches can be taken to reduce the impact of the borer and increase the chance for the tree to overcome the situation. The first approach is to increase the vigor of the tree. This is done by identifying the stress factor(s) that contributed to the initial decline of the tree and take action to fix it. The second is to use prescription Arborceuticals™ to treat the borer infestation. Rainbow Treecare uses two forms of Arborceuticals to treat for borers. Systemic control is initiated using a botanically-based product (Xytect™ ) that is applied to the soil and is taken up through the roots and distributed throughout the tree by the xylem tissue. This treatment is very effective if the damage to the living wood tissue is not too severe. The other product (Permethrin), also botanically-based, is used as a barrier spray on the trunks of the trees to prevent larvae from borer eggs from entering the tree.

As with any tree pest or disease problem the best approach is to prevent the problem from happening. Keep your trees healthy and make sure that they get an annual check up. If decline or other evidence of insects is observed, contact your Consulting Arborist mmediately to diagnose the condition. A healthy tree is the best defense.

 

Photo credits:
Robert A. Haack, Bugwood.org, Joseph O'Brien, Bugwood.org, David Cappaert, Bugwood.org, Pennsylvania Department of Conservation and Natural Resources - Forestry Archive, David G. Nielsen, Bugwood.org, Whitney Cranshaw, Bugwood.org, Joseph Berger, Bugwood.org, James Solomon, USDA Forest Service, Erich G. Vallery, USDA Forest Service - SRS-4552, Minnesota Department of Natural Resources Archive, US Fish and Wildlife Service's Digital Library System, Clemson University - USDA Cooperative Extension Slide Series, Carroll E. Younce, USDA Agricultural Research Service, Ohio State University, 2004, Ronald F. Billings, Texas Forest Service, William M. Ciesla, Forestryimages, Stanislaw Kinelski, Entomology Dept., Univ. of Minnesota, J.R. Baker & S.B. Bambara, North Carolina State University, Darren Blackford, USDA Forest Service