ASIAN AMBROSIA BEETLE

Xylosandrus crassiusculus

By Horticulture Program Assistant

Louise Weyer

Description:  Adult females are minute (2 to 3 mm), dark reddish brown, have stout bodies with a hunched-back appearance.  The males are slightly smaller, flightless, and less numerous than females.  They mate, lay eggs and rear their young within the galleries.  Larvae are white, legless, and C-shaped.  Mature females leave infested plants and fly to new hosts.  High humidity is required for successful reproduction.  The beetles are most active in March and April but remain active at low levels throughout summer and fall.  It takes an average of fifty-five days to complete a generational cycle.  There are two generations per year.

Host Plants:  The beetles attack various trees and shrubs, i.e., pecan, cherry, peach, plum, persimmon, oak, elm, sweet gum, magnolia, fig, buckeye, golden rain tree, redbud, hickory, Japanese maple, and crape myrtle.   Attacks on living plants usually are near the ground level on saplings or at bark wounds on larger trees.

Damage:  Females bore directly into the heartwood of twigs, branches or small trunks of woody host plants at the rate of one inch per day, excavating a system of tunnels or galleries and introducing an ambrosia fungus.  The adults and larvae feed on the fungus rather than the wood of the host plant.  The boring and fungus disrupt the host’s vascular system which results in the demise of part or all of the host.  They will attack healthy plants as well as those in stress. 

Symptoms:  Presence of beetles in a host can be identified by toothpick-like spines of boring dust protruding from holes bored in the plant by the females.  The spines may be 2 to 3 inches long, but are fragile and easily broken off by wind and rain.  A fine frass (comparable to talcum powder) may be seen at the base of the plant.  Sudden wilting of new foliage as the plants are leafing out and sap running from small holes are other signs of an ambrosia beetle attack.

Control:  If there are 25 to 200 holes in the trunk or limb, the plant should be removed and burned.  Do not leave it in your landscape.  Since almost the entire life cycle of the beetle is spent inside the plant, it is difficult to control them with insecticides.  Fungicides are ineffective against the fungus. 

Trees become less attractive to beetles once leaves are fully expanded.  Insecticide applications to susceptible plants during the time spring flush is developing may help reduce infestations.  Up to four applications of a pyrethroid spray repeated every ten to fourteen days is required.  Sprays are not recommended in the fall.  This is expensive and may not be necessary in most years.  Read the label and carefully follow the manufacturer’s instructions.

References:  Asian Ambrosia Beetles, Georgia IPM, University of Georgia   www.gaipm.org

                    Asian Ambrosia Beetles, University of Arkansas, www.uaex.edu

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