Granulate ambrosia beetle
Click for larger image Sawdust tubes (toothpicks) produced by granulate ambrosia beetles (Coleoptera) on redbay (Persea borboinia). A. (Bud) Mayfield, USFS, Bugwood.org

Introduced from China in the 1970’s, the granulate or Asian ambrosia beetle was first found in Missouri in 2002. Female beetles cause damage to fruit trees, nut trees and other woody ornamentals by boring extensive tunnels in the wood of their hosts and by introducing fungi. This aggressive pest is of concern because it has a wide variety of hosts and unlike many pests, will also attack apparently healthy plants.

Symptoms and Diagnosis

Granulate ambrosia beetles (Xylosandrus crassiusculus) infest over 100 different kinds of plants; common hosts include fruit trees, nut trees, golden rain tree, dogwood, magnolia and maples. Symptoms of infestation include 2 mm round entrance holes in trunks of young trees and in branches 1 to 2.5 inches in diameter. Toothpick-like strands up to 1.5 inches long made of frass and boring dust protrude from these holes. Tree species which produce large amounts of resin may also exhibit gummosis or oozing sap at the entrance holes. Ambrosia fungus and Fusarium spp. fungus, introduced by the beetle, may block water transport through the tree’s vascular tissue resulting in wilted foliage and fungal staining in infected wood. The infested plant may die from the boring damage or from the fungal infection, especially if it is attacked during the leafing out stage or if it is a younger plant such as nursery stock. The surface damage caused by these beetles is similar to that of the shot hole borer, however, shot hole borer damage only goes just past the bark.

Life Cycle

Female granulate ambrosia beetles are reddish to blackish brown, cylindrical in shape and 2 to 2.5 mm long. Male beetles are smaller than the females and remain in the host plant. In spring the female beetles mate and then fly to another host plant. There they excavate extensive galleries, inoculate the wood with ambrosia fungus for a food source and rear their young. Host plants may be infested by one to 50 or more beetles.

Integrated Pest Management Strategies

1. Practice good cultural techniques to keep plants healthy and free of drought, nutritional or injury-induced stress.

2. Monitor plantings for signs of beetles by setting out traps and looking for the toothpick–like frass and boring dust strands.

3. If beetles are detected in the traps, apply a preventative spray of a pyrethroid-based insecticideCyfluthrin , or Bifenthrin . Reapply every two to three weeks while beetles are active.

4. Destroy infested plants or plant parts. Insecticides are not effective once the beetles are inside the wood.

5. Many previously recommended insecticides such as lindane, dursban and systemic pesticides are no longer considered effective and are no longer available or registered for this use.

Organic Strategies

Strategies 1, 2, and 4 are strictly organic approaches.

More images:

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Sawdust tubes caused by the granulate ambrosia beetle in Japanese maple (Acer) trunk.
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Larvae of granulate ambrosia beetles (Coleoptera). W. Hudson, UGA, Bugwood.org
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Adult granulate ambrosia beetle (Coleoptera). N. Wright, FL-DACS, Bugwood.org