Hickory Bark Beetle (Scolytus quadripinosus (Say.))

L. Tucker, E. Czerwinski, T. Scarr

Ministry of Natural Resources, Forest Health and Silviculture Section

Background

Figure 1 - Hickory bark beetle larval galleries

The native hickory bark beetle is considered the most destructive pest of hickories. Like other bark beetles native to Ontario, it is attracted to trees previously weakened by other factors such as drought. Hickory is an important forest ecosystem component in southern Ontario. This insect attacks and kills hickory trees and has been a serious forest health issue in recent years.

Hosts

In Ontario, hosts are primarily bitternut hickory, Carya cordiformis (Wangenh.) and shagbark hickory, Carya ovata (Mill.). Elsewhere, pecans, Carya sp., and butternut, Juglans cinerea (L.) are also attacked.

Figure 2 - North American range of hickory species (Map courtesy of the USDA)

Current Situation

The recent population increase of hickory bark beetle in southern Ontario is likely linked to the drought conditions experienced in 2001, 2002 and 2005. The hickory bark beetle tunnels in the bark and sapwood of hickory trees which can cause rapid decline in tree health. Larval galleries (Figure 1) in the main stem and large branches disrupt the host tree’s ability to transport nutrients and water. Heavy shoot damage and foliage feeding by adults severs the leaves and twigs which hang or drop to the ground.

Range

Hickory bark beetle occurs throughout the natural range of hickory, Carya sp. (Figure 2).

Description

Figure 3 - Adult hickory bark beetle with exit holes

Adults are short (4 to 5mm long), stout, cylindrical, and dark brown to black (Figure 3). Larvae are short (5 to 8mm long), curved, and yellowish-white, legless with a wrinkled appearance. Pupae are compact and white. Eggs are not usually visible to the naked eye.

Life Cycle

Adult beetles emerge from tiny round exit holes, roughly 3mm in diameter (Figure 4), May to August and begin feeding in the crown at the base of leaf petioles and twigs. Once mature, adult females are attracted to weakened trees where they bore into the bark of the main stem and branches. Here they construct vertical galleries in the phloem and deposit between 20 to 60 eggs.

Figure 4 - Adult exit holes

Newly hatched larvae feed just beneath the bark, in individual feeding galleries radiating from the original egg gallery constructed by the adult female. Larvae overwinter under the bark at various stages of development.

Signs and Symptoms

Signs and symptoms include:

• thinning crown
• wilted leaves (Figure 5)
• dead twigs and limbs
• leaf yellowing and premature dropping of leaves
• epicormic shoots
• hanging (broken) twigs in crown
• tiny borer holes approximately 3mm in diameter (Figure 4)

  Figure 5 - Thinning hickory crown

• fine boring dust on bark and at base of tree
• presence of parasitic wasps around host tree and;
• an increase of woodpecker activity on host tree.

Foliage of heavily infested trees turns yellow then red within a few weeks.

Management and Control

Once infested with the hickory bark beetle, a tree usually dies rapidly. Preventative measures include maintaining healthy, vigorous woodlands by following Best Management Practices outlined in the Extension Note: Do You Have a Healthy Woodlot? It is available on-line as a pdf at the LandOwners Resource Centre.

For additional copies of this publication contact the Ontario Ministry of Natural Resources Information Centre at the number listed below.

FHA-1-2006