Wood-boring Insects Threatening Indiana Hardwoods

  By Nicole VanDerLaan-Hannon and Matthew Ginzel

Indiana has over 9 million acres of forest and timberland combined, and approximately 87% of the timberland in the state is in private ownership. Unfortunately, the sustainability of this resource is threatened by a litany of native and exotic insect pests, and increases in global trade will only further jeopardize the quality and productivity of Indiana’s forests. These insects are capable of reducing tree growth, causing stem deformities or a reduction in timber grade, affecting seed production, and ultimately killing a tree. This article is intended to provide landowners and forest managers with a brief overview of four invasive wood-boring beetles that are either currently found in Indiana or have the potential to enter the state.

Emerald Ash Borer (EAB, Agrilus planipennis); native to Asia and currently found in northeastern U.S. and spreading throughout Indiana. Hosts: Ash, attacks crown first then moves down trunk of tree, can colonize trees greater than 1” in diameter. Life Cycle: Adults are metallic-green (1/3” long) and emerge in late April (Fig.1), leaving D-shapedexit holes in the bark. Larvae are creamy-white and have a flattened body with bell-shaped segments (Fig. 2). They feed in the phloem creating S-shaped galleries. It can take up to three years for symptoms to appear following initial colonization.

Signs of Infestation: D-shaped exit holes, vertical splits in the bark, crown dieback, epicormic shoots, flagging and yellowing leaves. More information on EAB can be found at www.extension.entm.purdue.edu/EAB/.

Asian Longhorned Beetle (Anoplophora glabripennis); native to Asia and currently found in New York, New Jersey, Massachusetts and was recently eradicated in Illinois.

Hosts: Primarily maple and capable of attacking a variety of hardwoods.

Life Cycle: Adults (1-1 ½” long) emerge from July to August. They are primarily black in color with white spots on their backs and white bands on their elongate antennae (Fig. 3). Adults feed on leaves and twigs of host plants. Mated females chew oval depressions in the bark where they deposit eggs. Young larvae are creamy-white with dark brown mouthparts and feed on phloem. As the larvae grow, they bore deeper in the heartwood. It may take 1-2 years for larvae to develop into adults.

Signs of Infestation: Oval depressions chewed in the bark, sap exuding from 1/4” or larger round exit holes, “frass” or coarse sawdust near exit holes and at the base of trees, crown dieback, yellowing leaves and weakened branches. For more information, visit www.beetlebusters.info.

Black Stem Borer (Xylosandrus germanus); an ambrosia beetle from Asia, presently found throughout the eastern US including Indiana.

Hosts: Capable of infesting over 200 tree species including chestnut, black walnut, butternut, oak, black cherry, hickory and birch.

Life Cycle: Adults are dark brown (approx. 1/10” long) and emerge in May (Fig. 4).

Fertilized eggs become females and  unfertilized eggs become males. Flightless males remain inside the host and females mate with either male siblings or male offspring in order to produce fertilized eggs. After locating a host, females chew brood chambers in the heartwood and introduce a symbiotic fungus or “ambrosia” which grows on the walls of the chamber. Larvae feed solely on the fungus. This borer is capable of colonizing healthy trees.

 Signs of Infestation: Entrance holes 1/10” in diameter, epicormic shoots and long strands of sawdust or “frass” protruding from holes resembling toothpicks (Fig. 5). For more information, please visit www.extension. purdue.edu/extmedia/FNR/FNR-227-W.pdf.

Walnut Twig Beetle (Pityophthorus j uglandis); a bark beetle native to the western U.S. where it has killed large numbers of black walnuts. The beetle has recently been found in Tennessee.

Hosts: Prefers black walnut, but capable of infesting other walnuts.

Life Cycle: Adults emerge in May and are present throughout October. They are yellowish-brown and are  1/10” long (Fig. 6). Larvae are creamy white and feed under the surrounding bark. Adults introduce a Geosmithia fungus that stains the wood and creates multiple cankers in the bark – a condition called “Thousand Cankers Disease”.

Signs of Infestation: Entrance holes approx. 1/10” in diameter, dark amber stains in the wood and cracks of the bark, multiple brownish-black cankers, early signs of flagging and crown dieback (Fig. 7). For more information, please visit www.ppdl.purdue.edu/PPD/pubs/walnutthousandcankersdisease/pdf.

Control: Chemical control is rather ineffective against wood-boring insects because they spend the majority of their lives concealed beneath the bark of trees, physically protected from sprayed insecticides. Nevertheless, damage by many of these insects can be minimized by maintaining a healthy tree stand through proper sanitation, such as removing dying and diseased trees, and thinning to reduce stress. If landowners or forest managers find one of these insect pests or signs of infestation they are encouraged to consult their local Department of Natural Resources or University Extension personnel to confirm the identity of the insect and for current management tactics and control measures.

Nicole VanDerLaan-Hannon is a graduate student in the Department of Forestry & Natural Resources at Purdue University. Matthew Ginzel is an Assistant Professor of Forest Entomology in the Departments of Entomology and Forestry & Natural Resources at Purdue University.

Barnd, B. D., Pijut, P. M. and Ginzel, M. D. (2008) Insects Affecting Hardwood Tree Plants. Purdue University Extension. FNR- 227-W. (http://www.extension.purdue.edu/extmedia/FNR/FNR-227-W.pdf).

Cranshaw, W. and Tisserat, N. (2010) Pest Alert: Walnut Twig Beetle and Thousand Cankers Disease of Black Walnut. Colorado State University. (http://www.ext.colostate.edu/pubs/insect/0812_alert.pdf).

United States Department of Agriculture (2006) Invasive Species and Forest Health Factsheet. Animal and Plant Health Inspection Service. (http://www.aphis.usda.gov/publications/ plant_health/content/printable_version/fs_invspec_forest_health.pdf).