Illinois Natural History Survey - University of Illinois

Insect Invaders Infest Chicago Trees

The Forest Preserve Districts of Cook and DuPage counties afford Chicago residents and visitors alike a touch of wilderness amid the towering skyline and bustling thoroughfares of the city. In fact, last year more people used Cook County's forest preserves than visited Yellowstone National Park. But a most unwanted visitor, the Asian longhorned beetle, also finds these 90,000 acres of preserve and the 500,000 trees lining the streets of the city of Chicago quite appealing.

The first Illinois infestation of the Asian longhorned beetle was discovered in the Ravenswood neighborhood of Chicago in July 1998. Soon to follow were detections of much smaller infestations in Addison (DuPage County) and Summit (southern Cook County). Illinois' battle with the Asian longhorned beetle had begun.

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Trees in the Ravenswood neighborhood of Chicago were cut down as a result of damage by invading Asian longhorned beetles.

Survey crews armed with binoculars were quickly dispatched throughout the neighborhoods in search of infested trees, but authorities soon learned that ground searches alone were inadequate. The telltale signs of infestation, dime-sized adult exit holes or the much smaller egg-laying sites, were often well concealed and high in the tree canopies. In March 1999, bucket trucks and tree climbers (mostly U.S. Forest Service smoke jumpers) were added to the arsenal of survey tools and many more infested trees were identified. Regrettably, removal and destruction of infested trees are currently the best tools available to eliminate and control the Asian longhorned beetle. Since the damaging larval stage lives deep inside infested trees during most of the year, conventional insecticide sprays are not an option, and lures are not available to attract adults.

Tree-cutting operations began in the Ravenswood community in February 1999. Within a matter of days, 837 trees were felled, chipped, and burned. Portions of the once tree-lined streets of Ravenswood were suddenly barren and the onslaught continues. An additional 314 infested trees were discovered during intensive survey efforts in 1999, while 54 trees were felled in Addison and 24 succumbed in Summit.

Although residents were not held responsible for the cost of tree removal, their losses were immeasurable. What is the value of a tree in the city? A mature city tree not only provides beauty but also offers many practical benefits such as summer shade; winter wind protection; reductions of air, water, and noise pollution; natural habitats; and increased property values. But to many, the emotional loss was perhaps the most profound; an old friend was no longer there to greet them each day.

Even so, residents agreed to these heroic measures in hope of preventing a similar fate for other neighborhoods or the beloved parks and forest preserves of the city. More than 11% of Cook County is a forest preserve and the majority of trees are acceptable hosts for Asian longhorned beetle. According to city foresters, 50% of Chicago's trees are maples, which happen to be one of the beetle's favorite foods, and overall 70% of the city's trees are susceptible. Clearly, the potential for a replay of the Dutch elm disease disaster of the 1950s (which coincidentally also struck the Ravenswood neighborhood) is a possibility.

With this in mind, the selection of trees for replanting has been done with extreme care. A variety of oaks and lindens, catalpa, Kentucky coffeetree, Turkish filbert, gingko, tulip tree, and honey locust have been chosen to replace those sacrificed to the Asian longhorned beetle. Our current knowledge of the beetle's host range suggests that these replacement trees are resistant to Asian longhorned beetle attack. City foresters began replanting operations during summer 1999 with balled and burlapped trees up to 18 feet tall, again at no cost to homeowners. Still, it will take many years of tender care before the replacements can hope to once again rise above the rooftops. Throughout this process of regrowth, landscapes may well dramatically change--an ecological succession of sorts. For instance, shade-tolerant shrubs, flowers, groundcovers, and vines that once thrived in canopied yards will face much stronger summer sun and may not survive. In some cases, this may require periodic replacement of understory plantings as the tree canopies gradually grow denser.

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More devastion in the Chicago area caused by infestation of Asian longhorned beetles.

The city's struggle with the Asian longhorned beetle continues. Although adult beetles were difficult to find in 1999 and far fewer infested trees were located, regulatory officials are far from saying the battle is won. Fortunately, the Asian longhorned beetle is not a particularly strong flier and does not appear to be rapidly expanding its range; however, several new spot infestations were found outside the quarantine boundaries, including four trees in a forest preserve. Intensive surveys and tree removal will likely continue for five or more years at a cost of several million dollars before we will know with certainty if eradication attempts are successful and the Asian longhorned beetle becomes a distant memory. But residents of affected neighborhoods will get a daily reminder of the impact of this conflict for many years to come--just by looking out their windows.

Charles Helm, Center for Economic Entomology

Charlie Warwick, editor



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