Illinois Natural History Survey - University of Illinois

Illinois Corn Cob a Weapon Against Insect Pests

Integrated pest management (IPM) in Illinois is faced with numerous challenges. New pests, like the Asian tiger mosquito, a potential vector of numerous mosquito-borne diseases, were introduced into the state. Also, the pests that have been around for awhile are adapting to pest management practices; for example, the western corn rootworm thrives despite crop rotation practices, and many insect pests develop genetic resistance to synthetic pesticides.

These problems and the commitment of society and government to the reduction of the amount of insecticides applied in urban and agricultural environments challenge our scientific capabilities to develop innovative pest management strategies that meet environmental goals while continuing the productivity of American agriculture. A potential weapon against insect pests of public health and agriculture includes the use of an abundant Illinois crop by-product--the corn cob.

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Corn cob granules can be formulated with small dosages of chemical and microbial insecticides, insect behavior-modifying chemicals (attractants and feeding stimulants), and a variety of insect pathogens (viruses, bacteria, fungi, and microsporidia). Granules can provide a variety of desirable characteristics, including a high degree of target specificity, short- or long-term persistence, delayed release of active ingredients, and a substantial reduction in the amount of insecticide used in the environment. 
The Asian tiger mosquito, an insect pest that corb cob granules are 
effective against.

In the mid-1970s, corn cob granules were appraised as a possible carrier of insecticides for mosquito control. Corn cobs were ground into particles ranging in size from 6 to 14 mesh that were able to penetrate both primary and secondary vegetative canopies. This was an important attribute because the aquatic habitats that produce mosquitoes include both wooded areas and open grassy sites. Efficiency of control, as well as the cost of application, are both optimized if as much of the insecticide as possible is delivered to the target organism with minimal environmental contamination or drift.

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Waste tire dumps are a major source of mosquito habitat for over a dozen pest and vector mosquito species. This includes the vectors of two mosquito-borne diseases that have plagued Illinois, St. Louis encephalitis and LaCrosse encephalitis. One of the main difficulties in treating large tire piles is the even dispersal of granules throughout the entire tire pile. Treatment of tires with liquid formulations is often problematic because of extensive runoff and poor penetration of interior tires. Cooperative experiments by the Medical Entomology Program of INHS, the Illinois and Chicago Departments of Public Health, and 
Western corn rootworm adult on corn leaf.

a commercial collaborator, Clarke Outdoor Spray Co., found that synthetic and microbial insecticides incorporated into the corn cob granules exhibited two important characteristics: a high degree of penetration into variously stacked tire piles and the slow release of toxicant, thus increasing efficacy and prolonging the period of activity. The corn cob was instrumental in providing not only a means of reaching "hidden" mosquito larval habitats but also provided environmentally safe, long-termcontrol.

The technology developed for mosquito control also has great potential to address a wide range of insect pest problems, such as the management of corn rootworms. Diabrotica barberi (the northern corn rootworm) and Diabrotica virgifera virgifera (the western corn rootworm) are the most expensive insect pests in Illinois with annual crop losses and treatment costs estimated at $100 million. Present control practices for corn rootworms based on crop rotations of corn and soybeans and the application of soil insecticides in continuous corn are frequently less than satisfactory. Changes in rootworm behavior threaten the use of crop rotation, and variable environmental factors, such as temperature and precipitation, can greatly reduce the efficacy of soil insecticides. Furthermore, the broad use of synthetic pesticides has introduced many new problems, including insecticide resistance, microbial degradation of insecticides, the elimination of beneficial insects, the emergence of secondary pests, acute toxicity to applicators, and environmental contamination resulting in pesticide residues in humans and wildlife. These are major reasons for exploring alternative pest management techniques that reduce the application rates of insecticide in the environment.

Extensive research is being focused on the use of baits directed at suppressing adult corn rootworm populations prior to mating and oviposition. The bait technology, combining rootworm feeding stimulants, volatile attractants, and insecticides with various carriers, was originally developed at the University of Illinois. Cucurbitacin and insecticide formulations on corn granules and dried hybrid squash produced high beetle mortalities when aerially applied at about 10 kg per ha. The total amount of insecticide applied was dramatically reduced by at least 90% over soil applications, about 30 grams of insecticide per ha, and the feeding stimulant content (cucurbitacins) was only about 1 gram per ha. Field tests in Illinois indicated the bait was highly specific for corn rootworms with little impact on predators.

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Aero-GunTM applicator mounted on trailer.

Research progress with granular technology has been hampered by the lack of a simple applicator to disperse the granules in relatively broad swaths. Aerial application is relatively costly and requires specialized equipment for bait application. Backpack sprayers are considerably more effective than hand distribution, but generally only disperse granules over 10 to 20 meters. Recently, a new application method, the Aero-GunTM, was developed that allows the precise, even coverage with corn cob granules of an area of over 30 meters and a lateral pattern varying from 5 to 10 meters. The entire unit is mounted on a trailer and granules can be applied while the vehicle is stationary or in motion.

Preliminary results on the distribution of granules from the Aero-Gun indicate this equipment may be used in a variety of future studies on the control of floodwater and container mosquitoes as well as corn rootworms and other agricultural pests.

Richard Lampman and Robert Novak, INHS Medical Entomology Program; Robert Metcalf, INHS and University of Illinois.



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