Asian Ambrosia Beetle

9 June 2008

Virginia Cooperative Extension, Charlottesville/Albemarle County Office
460 Stagecoach Road, Charlottesville, Virginia 22902
phone: 434.872.4580   fax: 434.872.4578

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As spring weather brings our plants back into action it also inspires insects to get back to work. Often we discover insects damaging plants in the spring when trees or shrubs fail to leaf out or wilt and drop their leaves soon after leafing out.

One striking example of this is the evidence seen from the feeding of the Asian ambrosia beetle. The toothpick-like tubes excavated by these beetles are diagnostic for their presence.

The Asian ambrosia beetle was first detected in the U.S. when it infested peach trees in Charleston, South Carolina in 1974. Since then it has spread to other parts including Virginia.

Toothpick-like spines protruding up to 1.5 inches from the host plant can identify infestations. The spines are strings of boring dust produced by the female beetle as she excavates her gallery. The spines are fragile and are easily broken off by wind or rain. Individual plants may host from one to more that 50 individual beetles. Although adults can be captured most of the year, trap data indicate they are most active during early spring.

The Asian ambrosia beetle is a small, but deadly-to-trees insect. It has a wide host range of trees, mainly infesting small diameter, smooth bark sections of trees. Peach, pecan and plum orchards have been attacked, as well as nursery tree stock. Other known hosts include cherry, persimmon, golden rain tree, sweet gum, Chinese elm, magnolia, fig, and Mexican buckeye. The ambrosia beetle is showing up in a wider range of plant material. We found them in London plane, river birch, zelkova, dogwood, sugar maple, sweet bay magnolia, and Styrax.

Females bore into twigs, branches, or small trunks of susceptible woody plants, excavate a system of tunnels in the wood or pith, introduce the symbiotic ambrosial fungus, and produce a brood. Like other ambrosia beetles, they feed on ectosymbiotic fungi which they introduce into their tunnels and cultivate and not the wood and pith of their hosts. Eggs, larvae, and pupae are found together in the tunnel system excavated by the female. There are no individual egg niches, larval tunnels, or pupal chambers. It breeds in host material from 2 to 30 cm in diameter, although small branches and stems are most commonly attacked. Attacks may occur on apparently healthy, stressed, or freshly cut host material. High humidity is required for successful reproduction. Attacks on living plants usually are near ground level on saplings or at bark wounds on larger trees. Females remain with their brood until maturity. Males are rare, reduced in size, and flightless. Females mate with their brother(s) before emerging to attack a new host.

The beetles of the first generation are in the larval stage at this time. You can apply Onyx or Astro now to try and control the second generation that will come out at the end of June. There will already be damage from the first generation of beetles.

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For more information about this and other landscape topics contact your local Virginia Cooperative Extension office. The local Virginia Cooperative Extension office numbers are Albemarle 872-4580, Fluvanna 591-1950, Greene 985-5236, Louisa 540-967-3422, and Nelson 263-4035.