Pesticide resistance: Modes of action are important criteria in selecting insecticides so as to prevent the development of resistance to insecticides. Rotate chemicals with a different mode-of-action group number, and do not use products with the same mode-of-action group number more than twice per season. For example, pyrethroids have a group number of 3A; chemicals with a 3A group number should be alternated with chemicals that have a group number other than 3A. Mode of action groupings are assigned by IRAC (Insecticide Resistance Action Committee). For additional information, see their Web site at http://www.irac-online.org/.