To make it easy to recognize different classes or modes of action, the Insecticide Resistance Action Committee (IRAC) has created a classification scheme that distinguishes modes of action by group numbers. IRAC is an industry-organized group of pest management specialists that develops resistance management guidelines for global implementation. The U.S. Environmental Protection Agency requested agricultural chemical companies to voluntarily include the IRAC MOA group number in a standard format on the insecticide label (example below). Products sharing the same group number have the same MOA. When a premix label displays the group number(s), the user can easily determine the modes of action included in the premix.
The complete IRAC MOA classification scheme (browse, download PDF, or get the App here) has an alphabetized listing of active ingredients with MOA group number and letter designations. Nearly half of the MOA groups have subgroups specified by a letter (e.g., 1A and 1B). Insecticides in a subgroup (e.g., 1A Carbamates) have the same MOA as others in the main group (e.g., 1B Organophosphates), but differ from them in chemical structure. Because of this structural difference, insecticides in one subgroup are likely to be metabolized by different enzymes and may bind differently to the target site of action than members of another subgroup(s). In the absence of other alternatives, it may be possible to rotate insecticides between subgroups if it is clear that cross resistance mechanisms do not exist in the target populations. Consult local expertise or see the IRAC MoA Structure Poster for more information.
Resistance management strategies can differ for a specific combination of crop, insect, insecticide, and geographical area. In addition to citing MOA group numbers for a rotation scheme, remember to always follow the resistance management recommendations printed on the insecticide label. Labeling information will indicate how to reduce the potential development of resistant pests and the conditions under which product rotation to a different MOA is needed. Contact your local Extension educator, certified crop advisor and/or manufacturer for resistance management recommendations for specific crops and insects.
Compiled by Dr. Wayne Buhler, PhD
Topics Included in this Module
- Introduction to Insecticide Resistance
- Is Resistance to Blame? — Resistance is not the only reason for insect control failure.
- Raised Resistance Risks — Conditions that favor increased potential for resistance to develop and spread.
- Insecticide Resistance Mechanisms — There are several ways that insect populations can become resistant to insecticides.
- Take Steps to Avoid Insecticide Resistance — Ways to slow and prevent insecticide resistance from developing.
- Insecticide Spraying by the Numbers — Insecticide classification scheme that distinguishes modes of action by group numbers.
- What can you do about Resistant Insects? — What you can do if resistance is already present.
- Resources and Suggested Reading — Additional information about insecticide resistance.