Bark and ambrosia beetles are some of the most destructive insect pests attacking woody trees.
Distribution and Hosts
The fruit-tree pinhole borer, also called Asian ambrosia beetle, was first described from southern Germany (Cognato 2005); it is commonly found in the forests of Europe, Africa, and Asia. It is also now present as an introduced species in North America (United States and Canada), Australia, and New Zealand (since 1957 ) (Walker, 2008; Cognato 2005).
It has a wide host range that includes ornamental trees, stone fruits and timber. Almost all conifers and hardwoods are susceptible (Walker, 2008). Economic damage to stone fruits, including apricots and plums has been particularly devastating (Steiner, 2003).
Description of Damage
The adults are cylindrical, dark brown with yellowish hairs, and about 2.5 mm (approximately 0.1 inches). The head appears to be hidden under the thorax when viewing the insect's top surface or dorsum. These beetles are reported to have three generations per year in Australia (Steiner, 2003).
It usually attacks diseased, unhealthy or stressed trees. Adult mated females bore tunnels through the bark, and lay eggs or oviposit in the heartwood. Tunneling causes yeast-like ambrosia fungal infections within the tree (Walker, 2008). Adults and larvae bore and feed on this fungus that is found growing on the larval faeces and tunnel walls. As the beetles bore into the trunk they leave frass that sticks out of the trunk like tooth picks (Steiner, 2003).
Affected trees will show various stages of decline. First leaves will turn yellow, then brown and finally tree death will occur (Walker, 2008).
Due to their small size and the abundance of possible scolytinae beetle pests, confirming identification is difficult. The adult beetles are yellow-brown to black. The outer wing covers or elytra are rounded with a pointed marginal granule at each side. Antennae are clubbed and have a squared, short appearance (i.e. obliquely truncate) (Walker, 2008).
Fruit-tree pinhole borers usually over winter as mature larvae or newly emerged adults. After over wintering, females lay their eggs within the tunnels. When larvae hatch, they continue to tunnel and feed from the ambrosia fungus that grows on the tunnel walls. Under ideal conditions, their life cycle is completed in approximately 2 months. Usually these beetles emerge on warm days that follow cool periods. When temperatures reach 21°C females start flying in search of new hosts (Steiner, 2003).
Chemical control may not be possible, but contact your local cooperative extension service for further management recommendations http://www.csrees.usda.gov/Extension/index.html. Prevention by keeping the trees healthy is generally the best management option (Steiner, 2003).
- Cognato, A. (2005). Monographic research of tropical bark beetles (Scolytinae: Xyleborinii): preservations and modernization of taxonomic expertise.
- Steiner, E. (2003). Common Pests of Summer Fruit in Western Australia. Western Australian Department of Agriculture. Found at: http://www.agric.wa.gov.au/pls/portal30/docs/FOLDER/IKMP/PW/INS/PP/HORT/BULLETIN4585.PDF
- Walker, K. (2008). Fruit-tree pinhole borer (Xyleborinus saxeseni) Pest and Diseases Image Library. Updated on 9/17/2008. Found at: http://www.padil.gov.au