The Asian ambrosia beetle, Xylosandrus crassiusculus (Motschulsky) is a minute ambrosia beetle that has been attacking pecans and ornamentals in east Texas since the mid 1980's. This insect was f1rst detected in the United states in South Carolina in 1974 and has since spread to North Carolina, Florida, Lousiana and Texas.

The range of host plants for this insect is very broad with 126 known host plants in the tropics. In the U.S., known hosts include pecan, peach, plum, cherry, persimmon, golden rain tree, sweet gumf Shumard oak Chinese elm, sweet potato and magnolia.

The Asian ambrosia beetle is very small but infestations can be quite obvious. Female beetles are 2.1 to 2.9 mm long, stout bodied and reddish brown. The males are much smaller, being 1.5 mm long and have a more hunch back appearance. Males are also flightless and much less numerous than females.

Infestations start with a female beetle boring in to a twig, branch or trunk of a host plant. Host material can range from 2 cm to 30 cm in diameter (approximately 0.8 inch to 11.8 inches). Unlike other wood infesting, beetles that seem to prefer trees under stress, the Asian ambrosia beetle will attack seemingly healthy trees.

Infestations by this beetle can be very obvious. When female beetles are excavating galleries they push out strings of boring dust which will resemble tooth picks. These protrusions can be up to an inch in length and are quite obYious, often with several hundred on an individual tree. After infestation, the beetles cultivate an ambrosia fungus which has been carried into the gallery by the adult.

The females then produce a brood and both the adults and the larvae feed on the fungus rather than the host plant.

Female beetles will remain with their brood until maturity. Upon maturity, females beetles will mate with their brothers before emerging. Unlike the shot hole borer where each individual emerges from a separate hole, Asian ambrosia beetles emerge from the tree via the-parental entrance hole.

Emergence and activity of these beetles seems to occur all year, but trapping and monitoring of adult beetle activity in east Texas shows a significantly higher activity in March.

Currently there are no effective control measures. Where infestations occur, infested plants should be removed and bumed. Any factor that may cause a tree stress should be eliminated. Trunk treatments with insecticides seem to reduce the amount of infestation, but are not 100 percent effective.

In a study in South Carolina peach orchards, nine insecticides were evaluated as trunk treatments for a related species of ambrosia beetle, Xylosandrus saxeseni.

Insecticides evaluated in the test were: cypermethrin, permethrin, fenvalerate, azinophosmethyl, phosmet, chlorpyrifos, parathion, methyl parathion and endosulfan. Because the insect spends most of its life in the host plant, insecticides with a longer residual seemed to provide the best control. The pyrethroids were not that effective and are not recommended for control.

The range and extent of damage caused by this insect is still being evaluated in Texas. If any infestations are noted outside the area indicated on the map, the author would like to be contacted.

The information given herein is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement by the Cooperative Extension Service is implied.

Educational programs conducted by the Texas Agricultural Extension Service are open to all people without regard to race, color, sex, disability, religion, age or national origin.

1993

Return to top of page

Return to Departmental Home Page

Last modified: March 18, 1997 by Edgar Cross