Threat of Exotic Beetles


Plant Science Day 2000 Short Talk

Dr. Chris Maier
Department of Entomology
The Connecticut Agricultural Experiment Station
123 Huntington Street, P.O. Box 1106
New Haven, CT 06504

Phone: (203) 974-8476
Fax: (203) 974-8502


Biodiversity is declining around the world. We humans are largely responsible for decreasing biodiversity because we constantly alter our surroundings in our quest for a better way of life. Our intentional and accidental introduction of non-native organisms plays a large role in reducing biodiversity. Lately, the actual and potential negative impacts of exotic animals and plants increasingly have been featured in the popular and scientific publications. Who hasn’t heard of at least one of the nasty exotics?—the Zebra mussel, which has invaded our lakes and rivers; the gypsy moth, which has defoliated our forests, the hemlock woolly adelgid, which kills our hemlock trees; the codling moth, which bores through our fruit; West Nile virus, which threatens avian and human health; purple loosestrife, which now dominates many of our wetlands; and chestnut blight and Dutch elm disease, which have killed some our most valued forest or shade trees.

I do not want to give you the impression that all exotic plants and animals are bad. Obviously, many intentionally introduced plants have become valuable sources of food and fiber—just look around Lockwood Farm. Many of these plants do not become invasive—that is, they do not sweep through habitats and soon dominate the vegetation. Certain exotic species have helped to control pest species. In classical biological control, exotic herbivorous, predaceous, or parasitic insects are imported and released to control exotic pests. But, increasingly, scientists are concerned about how released animals affect non-target native animals and plants that are not pests. Some beneficial insects, such as the Halloween beetle, a ladybird beetle, have now become nuisance pests in homes.

Within the past 10 years, many new harmful exotic insects have been found within 100 miles of New York City—in our neighborhood! You have probably heard of one or more of these insects—the Asian longhorn, a beetle that bores into and kills many trees, but especially maples in urban areas; the small Japanese cedar longhorn, a beetle that tunnels into arborvitae and other woody landscape plants; the apple tortrix, a Japanese caterpillar that eats apple leaves; the green pug, a Eurasian caterpillar that eats apple and pear blossoms; and, the list goes on and on.

Today I’ll briefly profile two exotic beetles—the Asian longhorned beetle, Anoplophora glabripennis, and the small Japanese cedar longhorned beetle, Callidiellum rufipenne (Poster with common and scientific name of the two beetles). I encourage you to visit my field plot # to see specimens of these beetles and to learn more about their biology. These beetles are but two examples of the many exotic wood-boring beetles that relatively recently have been introduced into our country from eastern Asia. Why the influx of beetles of eastern Asia? First, imports from eastern Asia, especially China, have increased dramatically during the last two decades. Between 1975 and 1995, the value of imports from China increased more than 100 times—or about 10,000%. Second, boring beetles are particularly difficult to detect in imported wood. Larval beetles commonly are concealed in wooden packing or shipping materials, such as pallets, crates, and dunnage. Between 1985 and 1996, the Animal and Plant Health Inspection Service or APHIS of the United States Department of Agriculture found about 5,900 infestations of exotic insects in imported wood articles. Of these interceptions, nearly 94% were beetles. Thus, many have concluded that exotic wood-boring beetles pose a major threat to our forests, nurseries, and farms. Old and new regulations that require debarking, fumigation, or heat-treatment of wood should help to reduce the number of future introductions.

The Asian longhorned beetle has been in the headlines lately. This exotic wood-boring beetle probably reached our shores in wood articles shipped from China. The first infestation was detected in the Brooklyn area of New York in 1996, and soon the beetle was found in other nearby communities. In 1998, the beetle was also found in Chicago. Fortunately, based on surveys, especially near ports, the Asian longhorned beetle has not been found in Connecticut. The situation in Chicago was summarized in an article in Time titled "Naked City: How an Alien Ate the Shade." This beetle strikes fear into the hearts of city residents and officials, foresters, maple syrup producers, and others because it can kill healthy trees. Regrettably, at present, the only effective control method is to remove and to destroy infested trees.

In the few years since its introduction, much has been learned about the biology of this beetle (Photograph of beetle and damage). Adults are handsome black-and-white beetles that are 1 to 1-1/2 inches in length. Adult activity usually extends from May to October, with most activity in summer and early fall. After adults emerge from the wood, they mate on host trees. Then females munch on twigs for a while before they lay eggs in small pits that they have excavated in the bark of maples and other preferred hosts. After the larvae hatch, they bore into the cambium and then the sapwood and heartwood, creating tunnels 6 to 12 inches long. Larvae feed into the fall and sometimes into the following spring before they form pupae. When full-grown, the larvae approach 2 inches in length. When many larvae bore into the same tree, they can kill it.

Because of the risk that this beetle poses to urban trees and forests in the United States, experts decided to attempt to eradicate it by destroying all infested trees in New York and later in Chicago. Imagine convincing homeowners, park officials, city officials, and others that you want to remove their trees, some up to 6 feet in diameter. The campaign to convince the public had to be well-organized and funded. Flyers on the appearance, biology, and destructive potential of the beetle had to be prepared in many languages and distributed. A few are shown here (Poster of USDA and state publications). Many public meetings had to be held. And, perhaps most importantly, officials had to promise to replace the destroyed trees.

Once eradication had been endorsed publicly, officials began their enormous task. Infested trees had to be located by finding egg-laying scars or emergence holes or by using infrared photography (Infrared photograph used to detect infested trees). Then, the trees had to be cut down, removed, chipped, and burned. New trees, hopefully ones not susceptible to beetle attack, had to be planted. The grand plan is to survey for 5 years after the last infested tree is found. To date, the New York operation has cost $5-8 million dollars, and over 4,800 trees have been destroyed. In Chicago, about 1,400 trees have been cut down. The success of the eradication effort is questionable. Every year new, usually smaller, infestations are found farther from the sites of initial infestation. The battle probably will continue for years to come.

Our second problem beetle is the small Japanese cedar longhorned beetle that was found in North Carolina in 1997 and in Connecticut in 1998. In Connecticut, larval beetles had bored into the wood of live arborvitae in garden centers. By contrast, in its native Japan, the beetle mainly is found in the dead and dying wood of Japanese cedar and cypress. Once the beetle was discovered in Connecticut, The Experiment Station took quick and decisive action to protect the thriving nursery industry in the state. To decrease the spread of the beetle, the infested coastal counties were quarantined by the state, and inspections were intensified. Any trees shipped out of infested counties had to be certified to be beetle-free. Infested plant material was confiscated and destroyed. Unfortunately, as with the Asian longhorn, at present the only proven method to control the beetle is to destroy infested plant material.

We suspect that this cedar beetle has been here for a minimum of 5-10 years. How did the beetle get here? Much like the Asian longhorned beetle, it probably arrived in imported wood. Port inspectors have intercepted the small Japanese cedar longhorned beetle over one thousand times. Most finds are in cedar wood, particularly dunnage, from eastern Asia. Dunnage is material used to protect and support cargo in a ship’s hold. Dunnage could easily be knocked overboard during the unloading of cargo, or adult beetles could emerge from the wood and fly to the nearby shore where trees in the cedar family are sometimes plentiful.

We have learned much since the small Japanese cedar longhorn was discovered in Fairfield and New Haven Counties in 1998. We know that the adults, which live about 20 days, are active between late March and early June. The adult beetles are about 1/2-inch in length (Photograph of adults). The male is mostly iridescent bluish black with red at the corners of the wing covers, and the female is mostly reddish brown. Adults mate on their host plants, and then females lay eggs under bark, apparently without feeding. After hatching, the larvae bore under the bark to feed on the cambium and phloem. By the end of summer, larvae are full-grown (Photograph of full-grown larva). It is at this time that infested arborvitae often show obvious injury (First photograph of larval damage). The channels bored by the larvae may be seen on the branches and trunks. Larval tunnels are usually filled with a combination of excrement and chewed wood, giving them a "salt-and-pepper" look (Second photograph of larval damage). Once the larvae have stopped their feeding, they bore into the sapwood and carve an elongate pupal cell. Here they pupate, and then emerge as adults in about 2 weeks. The adults, however, are destined to stay in their pupal cell until the following spring. This species has just one generation per year.

This wood-boring beetle infests wild native coniferous trees, especially eastern red cedars. These trees may be the source of beetles that start new infestations in garden centers and yards. In the past 2 years, we have used cedar trap-logs and recently-cut trees to determine where the beetle is established in Connecticut and in nearby states. Trap-logs are merely sections of cedar trees that have sticky material on a plastic band placed around the center (Example of trap-log). Adult beetles become entangled in the adhesive material when they arrive to seek mates or to lay eggs. Based on our extensive sampling and other information, we know that this beetle is established in the wild in coastal states from North Carolina to Massachusetts. In Connecticut, the beetle has been trapped on logs or reared from dead trees in 33 towns in the 4 counties along the coast (Poster of distribution in the state).

Based on our field and laboratory studies, this exotic beetle can infest many coniferous plants. In the wild, it develops in the wood of Atlantic white cedar, eastern red cedar, and northern white cedar (arborvitae). In garden centers and yards, it also develops on false cypresses and junipers. The known hosts in Connecticut are American arborvitae, Atlantic white cedar, eastern red cedar, Hinoki false cypress, Sawara false cypress, and yellow cedar (List of known hosts). In the laboratory, the beetle completes development on all of the aforementioned plants and on bald cypress, Japanese cedar, firs, pines, and spruces. However, the trees in the cedar family, which includes true cedars, cypresses, false cypresses, and junipers, are probably preferred.

Plants that are stressed appear to be the most susceptible. Burlaped and bagged arborvitae imported from the western North America are particularly susceptible. These plants probably suffer from inadequate watering and from root and branch breakage before, during, and after shipment. Perhaps, the best defense against this beetle is to maintain good plant health.

Both the Asian longhorned beetle and the small Japanese cedar longhorned beetle bear close watching. Scientists are trying to develop monitoring traps with chemical attractants to improve detection, but much remains to be done. Chemical controls are being investigated. I have every reason to believe that soon we will know how to cope effectively with these pests. In the meantime, keep your plants healthy and let us know if you see any beetles matching the description of these dreaded wood-borers.