Since first being detected in the Chicago metropolitan area over two years ago, the Asian longhorned beetle (ALB) has been under steady attack by city, state, and federal officials hoping to eradicate this destructive new pest. Intensive surveys using bucket trucks and U.S. Forest Service tree climbers have helped define the boundaries of infestation, but to prevent the spread of ALB outside these areas, more than 1,300 infested trees have been destroyed. While this strategy appears to be working, aesthetic and financial losses have been mounting, while ongoing surveys continue to detect infested trees. Regulatory officials and homeowners have been somewhat frustrated by the limited arsenal of weapons to battle the spread of ALB. Currently, tree removal is the only available means of control.
However, recent developments could change the course of this battle. Field tests of various systemic insecticides conducted by USDA and Chinese researchers in the beetle’s homeland of China found that imidacloprid (commercially known in the United States as Merit or Imicide) may offer an effective means of protecting susceptible trees and help contain the spread of ALB. Preliminary results from tests in China showed both soil and trunk injections of imidacloprid readily transported the insecticide into stems, twigs, and foliage where newly emerged adult beetles feed before females deposit their eggs beneath the bark. This not only exposed many adult beetles to a lethal dose of insecticide but also produced some egg and early instar larvae mortality. This, of course, appears to be good news, but considerable testing in the United States will be necessary to determine the overall effectiveness of imidacloprid in the struggle against ALB. Will imidacloprid actually protect uninfested trees from future attack by ALB? If so, how long will it remain effective? What is the best application method? Will its effectiveness vary according to species of tree? Will imidacloprid help trees already infested with the beetle? All these and probably more questions must be answered before imidacloprid can be labeled and recommended for use against ALB.
To answer these questions, APHIS (Animal and Plant Health Inspection Service of the U.S. Department of Agriculture) scientists will be conducting a combined research and operational study on the usefulness of imidacloprid in the current eradication program. The research component will compare the effectiveness of soil injection to trunk injection at four different locations within the Ravenswood core infestation. At each location, researchers will select 60 susceptible, uninfested trees to receive the following treatments: (1) soil injection (15 trees), (2) trunk injection (15 trees), and (3) 30 untreated check trees. Each tree will be regularly monitored for signs of beetle infestation; and bark, twig, and leaf samples will be collected monthly for laboratory assays of imidacloprid presence, activity, and persistence. Results of this study should provide many answers to questions concerning the potential use of imidacloprid as a protective treatment.
The operational program can be viewed as a preemptive strike against the spread of ALB outside the known quarantine areas. Mass treatments of nearly 7,000 trees with trunk injections of imidacloprid are planned to create a “protected” buffer zone adjacent to the core infestation and at each of the outlying sites, including Addison and Summit. There is no guarantee that this approach will be effective, and infested trees will still be cut and chipped. But, based on results from the tests of imidacloprid in China and what we know about its use in the United States, there is reason for optimism. Imidacloprid is currently labeled for use against a wide range of sucking insect pests of trees and several soil and turf pests and has proved to be a safe, effective tool when properly used in sound integrated pest management programs. However, it is not yet legally approved for use against ALB; hence, the importance of the current studies. If it performs up to expectations, imidacloprid may prove to be another key weapon in the battle against this serious threat to our urban and national forests.