THE GRANULATE [ASIAN] AMBROSIA BEETLE
Prepared by Stephen Bambara & Christine Casey, Extension Specialists
CAUTION: This information was developed for North Carolina and may not apply to other areas.
THE GRANULATE AMBROSIA BEETLE Xylosandrus crassiusculus (Mot.), Coleoptera, Scolytidae [or Curculionidae Scolytini] Formerly known as the Asian ambrosia beetle.
This
tiny beetle is a pest of woody ornamental, fruit and nut trees throughout
North Carolina and can cause significant damage in nursery and orchard
settings. These beetles have many reported hosts. Among the most
common are styrax, ornamental cherry, Japanese maple, pecan, peach, plum, cherry,
persimmon, golden rain tree, dogwood, sweet gum, Shumard oak, Chinese
elm, magnolia, fig, and azalea. Mexican buckeye and sweetpotato are also
susceptible to attack.
This beetle was first detected in the U.S. in peach trees at Charleston, South Carolina in 1974. Since then it has become widespread, but localized in many North Carolina counties and most of the southeastern, Gulf coast, and surrounding states ranging from Texas through Oklahoma and east to Virginia. It has also been reported in coastal regions of Maryland.
It spreads by natural distribution and shipment of contaminated plant material.
DAMAGE:
Female beetles bore into the sapwood of stems and young trees. Though attracted
to damaged, stressed, or transplanted trees, this beetle also attacks seemingly
healthy, thin-barked hardwoods or branches from 1.0-2.5 inches in diameter.
Visible symptoms include wilted foliage and strands of boring dust protruding
from small holes. These insects make galleries directly into the heartwood of
the tree, which they inoculate with a fungus used as their food. The ambrosia
fungus that they use as food can block xylem vessels. In addition they can introduce
or create entry points for pathogenic fungi such as Fusarium spp. Infected
nursery trees often die, while landscape plants often seem to recover.
Serious attacks that result in tree death usually occur during leafing-out stage. Galleries into the sapwood may be observed by splitting a section of trunk or branch.
DESCRIPTION: These tiny blackish brown beetles somewhat resemble the Southern Pine Beetle. Infestations can be identified by toothpick-like strands protruding up to 1.5 inches from the host plant. The strands of boring dust are produced by the female beetle as she excavates her gallery. The strands are fragile and are easily broken off by wind or rain leaving only pencil-lead sized holes. Individual plants may contain from one to more than 50 individual beetles. (There are also some reports of Xylosandrus germanus producing toothpick strands.)
LIFE
HISTORY: NC records indicate they become active about the first of March
(it may be earlier) and peak about early April, however, they remain active
at low levels through the Summer and into the Fall. There may be two generations
in North Carolina. Females bore into twigs, branches, or small trunks of susceptible
hosts. They excavate tunnels in the wood, introduce a fungus and produce a brood.
A symbiotic ambrosial fungus is associated with this insect and may be partly
responsible for plant death. It is the growing fungus on which the beetles feed,
not the wood. Eggs, larvae and pupae are found together. There are no individual
egg niches, larval tunnels or pupal chambers. Attacks occur on stressed, transplanted,
freshly cut hosts, and even on apparently healthy trees. High humidity is required
for successful reproduction. Females remain with their brood until maturity.
Males are rare, small, and flightless and probably remain within the gallery.
New females mate with their "brothers", if present, before emerging to attack
a new host. Research at Tennessee nurseries determined that it took an average
of 55 days for the insect to complete one generation in that climate. Thus beetles
enter trees in early spring, oviposit, develop through to adulthood, and emerge
55 days later. Beetle flight is observed in the fall via traps, but tree entry
is typically not seen in the nursery. This provides strong anecdotal evidence
that they overwinter outside the nursery.
CONTROL: Heavily infested plants or plant parts should be removed and destroyed. It may be best for large growers to wait 3-4 weeks after trees are attacked before removal so as to concentrate and destroy the greatest number of beetles, possibly sparing some healthy trees. Once trees are infested, the beetle cannot be killed within the plant and fungicides are ineffective against the fungus. Protective sprays on trunks may be attempted on susceptible nearby plants. Earlier recommended sprays of lindane and dursban have shown to be largely ineffective and these chemicals are no longer available or registered for this use. Apply sprays after beetles are first detected in monitoring traps.
Any landscape borer spray containing a pyrethroid such as permethrin or cyfluthrin can be used but may have to be reapplied every two to three weeks while beetles are active. Keep trees healthy and avoid any unnecessary tree stress (drought, injury, nutrition, etc.). Check trees frequently beginning early March and treat accordingly. Organic products such as Pyrellin, Pyrenone or PyGanic may be used, but are expensive and may not be available in small amounts.
For commercial growers, Astro (permethrin) is registered for use on tree trunks in the landscape and may provide better protection. Tame + Orthene combination is another possibility if Astro is not available. For nursery sites Perm-Up and Permethrin Pro (permethrins) are still labeled. Multiple treatments may be needed during a season. (Note: Orthene has been phytotoxic to some crabapple varieties so it is best to confine spray to trunk and branches of crabapples.) Larger spacing in nurseries may help slow the spread from plant to plant. Plants that survive attack can often recover with age. Onyx (bifenthrin) is an often recommended trunk spray in landscape sites.
• Use traps to tell when beetles become active in your area.
• Use protective sprays of permethrin as soon as beetle activity
starts. Recent studies in VA indicate that applications of the highest labeled
rate of Astro (5.35 qt/100 gal) caused beetles to back out of galleries they
had already created. Although this is interesting, keep in mind that once beetles
are inside, pathogens may already be introduced.
• These insects do not consume plant material as they create their galleries,
so the systemic, Merit (imidicloprid), is not effective.
• Trees become less attractive to beetles once leaves are fully expanded,
so spray intervals can be extended or other pesticides may be used then. There
is no need to spray once flight stops, nor are sprays recommended in the Fall.
• Once a tree is attacked it becomes more attractive to further attack.
Use this to your advantage by leaving these trees in place to serve as trap
trees. So long as they are removed and burned before the 55-day life cycle
is completed, they should not be a source of beetle.
• Choose less prefered trees. In North Carolina, styrax and Yoshino cherry
are often heavily damaged. A Maryland study reported heavy damage to 'Stellar
Pink' dogwood.
ACTIVITY MONITORING
Some growers find ethyl alchohol based traps (Example 1) (Example 2) helpful to monitor for adult beetles in the Spring. These can be homemade soda bottle traps (Baker trap), Lindgren funnel traps, or modified Japanese beetle traps. Soda bottle traps are least expensive, but are less durable. The ethanol release strip purchased for use with the funnel trap tends to provide the most consistent lure release.
Useful References
Jason Oliver et al. "Comparison of Different Trap Types for Collection of Asian Ambrosia Beetles". SNA Research Conference, 2004, vol. 49
Russ Mizell and T. Riddle "Evaluation of Insecticides to Control the Asian Ambrosia Beetle, Xylosandrus crassiusculus". SNA Research Conference, 2004, vol. 49
Recommendations for the use of chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by the North Carolina Cooperative Extension Service nor discrimination against similar products or services not mentioned. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage and examine a current product label before applying any, chemical. For assistance, contact an agent of the North Carolina Cooperative Extension Service in your county.
Originally prepared by S. Bambara, K. Sorensen & J. R. Baker. Revised by Christine Casey & Stephen Bambara, March 2003. Some photos from www.bugwood.org/.
ENT/ort-111 August 2001, rev. March 2003
Web page last reviewed January, 2008 by the webperson.
