• Topics: Fishel, Frederick M  |  Pesticide Information Office  | Pesticide Labeling 

IRAC's Insecticide Mode of Action Classification¹

This guide explains the rationale behind the Insecticide Resistance Action Committee's (IRAC) insecticide and acaricide mode-of-action classification and provides a listing of those insecticide common names with their groupings and primary modes of action for insecticides currently registered in Florida.

What is IRAC?

IRAC has groups in several countries, including the United States, Brazil, South Africa, Spain, India, and Australia. An IRAC group's purpose is to provide agricultural producers and crop-protection professionals with information on resistance management. Members of an IRAC group are generally professionals who are actively engaged in the insecticide and acaricide manufacturing industry. Some university researchers also participate.

Resistance to Pesticides

Resistance refers to an inheritable change in the sensitivity of a pest population that is reflected in the repeated failure of a product to achieve the expected level of control when used according to the label recommendation for that pest species. Resistance does not always occur, but has been documented with insecticides as early as 1914, and there are many known instances today where resistance is a problem.

Resistance has not only occurred with insecticides, but also with other pesticides, such as fungicides, herbicides, and rodenticides. Complicating the understanding and management of resistance is the problem of knowing which type of resistance is present in a given pest population. For example, some pest populations are known to have cross-resistance. That is, they are not effectively controlled with pesticides having the same mode of action which generally target the same site within the pest. For example, both the carbamate and organophosphate insecticides target acetylcholine esterase although each group of insecticides is chemically different from one another. The greatest resistance concern arises when multiple-resistance is confirmed. Multiple-resistance is the situation of a pest population that is resistant to pesticides having different modes of action. Multiple-resistance is the most difficult type of resistance to manage because the number of management options is reduced. For more information on resistance, see EDIS Publication ENY-624,2005 Florida Citrus Pest Management Guide: Pesticide Resistance and Resistance Management, http://edis.ifas.ufl.edu/cg026.

IRAC's Classification Scheme

IRAC's insecticide-classification scheme is based on mode of action. The goal of the scheme is to provide information to applicators of acaricides and insecticides so that they can make sound decisions on selecting insecticides to prevent or manage resistance. Besides selecting products that have different modes of action, growers are also encouraged to integrate other methods into programs for insect and mite control. Table 1 contains those acaricides and insecticides registered for use in Florida in 2008. Keep in mind, however, these registrations change constantly. The registered acaricides and insecticides are listed according to IRAC's classification scheme by their group and subgroup codes, primary target site of action, chemical sub-group or exemplifying active ingredient, and active ingredient, based on that appearing in The Pesticide Manual, 14^th edition, 2006, edited by C.D.S. Tomlin, published by The British Crop Protection Council.

Using the IRAC Classification Scheme with Product Labels

IRAC is encouraging manufacturers of pesticides to indicate the IRAC mode-of-action group number and description on their product labels, and some registrants are doing so, especially with newer products. Such information would be helpful in assisting pesticide applicators in the selection of acaricides and insecticides for use in resistance-management strategies. One example the manner which IRAC suggests registrants list this information follows below.

Figure 1. 

Additional Information

• IRAC: http://www.irac-online.org/groups/guide.

• McCoy, C.W., M.E. Rogers, and L.W. Timmer. 2004. 2005 Florida citrus pest management guide: pesticide resistance and resistance management, EDIS Publication ENY-624, http://edis.ifas.ufl.edu/CG026. Entomology and Nematology Department, University of Florida, Gainesville, FL.

• Tomlin, C.D.S., ed. 2003. The pesticide manual: a world compendium, 13^th edition. The British Crop Protection Council. 1250 pp., ISBN 1 901396 13 4.

Tables

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other extension publications, contact your county Cooperative Extension service.

U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Millie Ferrer-Chancy, Interim Dean.

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