Cnestus mutilatus, Another Exotic Pest on the Move

Published: January 1, 2012

The camphor shot borer (also known as Xylosandrus mutilatus), is a species of ambrosia beetles that has been found in states close to Missouri. This shot borer is native to Southeast Asia and was first detected in Mississippi in 1999. Since then, it has been discovered in Hawaii, West Virginia, North Carolina, Georgia, Florida, Louisiana, Texas, Tennessee, Indiana, Ohio, and Arkansas. In early December, specimens believed to be the camphor shot borer were collected in East St. Louis, Illinois.

Figure 1. Camphor shot borer (Cnestus mutilatus) adult.

Figure 2. Cnestus mutilatus larva in a gallery.

Figure 3. Empty gallery following Cnestus mutilatus damage.

Adult shot borers are black (about 3.5 mm-long) with reddish-colored legs and antennae (Figure 1). They attack small diameter shoots of a wide range of hosts and excavate galleries in the wood. As the shot borers move between trees, they introduce fungal spores into gallery walls. Beetles deposit eggs in the fungus and larvae feed on the inoculum and can kill plant tissue. Larvae are white with a brownish head capsule and are legless (Figures 2 and 3).

In Asia, the camphor shot borer is a major pest attacking the trunk and branches of Chinese chestnut. This insect can attack over 200 plant species, including eastern black walnut, hickory, muscadine grape, sweetgum, flowering dogwood, red, sugar, and Japanese maple, yellow poplar, chinaberry, black cherry, winged elm, American beech, and hophornbeam. In a study conducted in Mississippi, shot borers were found on stressed trees including sugar maple with crown dieback, hophornbeam on a herbicide-sprayed right-of-way, flowering dogwood in a poorly drained soil, and sweetgum, hickory, winged elm, and muscadine grape seedlings after a prescribed burn. Camphor shot borers successfully attacked stems that were around 2 cm-diameter with a 2.2 m mean tree height. Reports from Tennessee indicate that the shoot borer not only infests stressed or dying trees, but also healthy, container-grown nursery stock. Symptoms of a shoot borer infestation include wilting foliage or twig dieback. When tissue is examined, pin-holes in the tree bark may bleed or light-colored boring dust is visible. Galleries in the xylem (wood) range from 1 to 4 cm-long with short brood chambers (Figure 2). Staining along galleries is also noticeable.

It is suspected that several of the exotic ambrosia beetle species were introduced into the United States in wood packing materials, crates or pallets. They may infest new sites with the movement of firewood, logs, lumber, or nursery stock. Female camphor shot borers can fly up to 3 miles to attack a host tree and they can also disperse by air currents. Alcohol traps are used to monitor these insects. For the granulate ambrosia beetle, pyrethroid insecticides can be used as a preventative control. However, once the beetles are inside trees, insecticides and fungicides are ineffective control measures. Additional information about various types of traps may be found at http://www.ces.ncsu.edu/depts/ent/notes/O&T/trees/note111/note111.html.

The camphor shot borer has not yet been found in Missouri. However, it is likely that may be found on nut or fruit trees, as well as ornamental landscape plants. If you suspect ambrosia beetle damage, please contact and/or send the insect to Doug LeDoux at the Missouri Department of Agriculture, 1616 Missouri Blvd., PO Box 630 Jefferson City, MO 65109 (email: Douglas.LeDoux@mda.mo.gov or by telephone at 573-751-5505).

Photos courtesy of Doug Stone, Mississippi State University