The Insecticide Resistance Action Committee (IRAC) was formed in 1984 and is now part of the Stewardship Steering Committee of CropLife International. IRAC provides a coordinated crop protection industry response to prevent or delay the development of resistance in insect and mite pests.
Developing new insecticides is becoming increasingly difficult and costly, so it is vital to protect the available effective products in the market place from the development of resistance by following insecticide resistance management (IRM) strategies in conjunction with integrated pest management (IPM). This is an essential element of responsible product stewardship.
The postal address for IRAC, via CropLife International, is:
326 avenue Louise, box 35
1050 Brussels Belgium
Tel +32 2 542 04 10
Fax +32 2 542 04 19
The contact point for IRAC enquiries is Alan Porter, IRAC Coordinator: [email protected]
The MoA Classification Scheme, developed and endorsed by IRAC, is based on the best available evidence of the MoA of available insecticides. Details of the listing have been agreed by IRAC member companies and approved by internationally recognized industrial and academic insect toxicologists and biochemists.
The aim of the MoA Classification is to ensure that insecticide and acaricide users are aware of MoA groups and that they have a sound basis on which to implement season-long, sustainable resistance management through the effective use of alternations, sequences or rotations of insecticides with different modes of action. To help delay resistance, it is strongly recommended that growers also integrate other control methods into insect or mite control programmes. Inclusion of a compound in the MoA Classification Scheme does not necessarily signify regulatory approval.
Resistance to insecticides may be defined as ‘a heritable 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’ (IRAC definition). Resistance arises through the over-use or misuse of an insecticide or acaricide against a pest species and results from the selection of resistant forms of the pest and the consequent evolution of populations that are resistant to that insecticide or acaricide.
In the majority of cases, not only does resistance render the selecting compound ineffective, but it often also confers cross-resistance to other chemically related compounds. This is because compounds within a specific chemical group usually share a common target site within the pest, and thus share a common MoA. It is common for resistance to develop that is based on a genetic modification of this target site. When this happens, the interaction of the selecting compound with its target site is impaired and the compound loses its pesticidal efficacy. Because all compounds within the chemical sub-group share a common MoA, there is a high risk that the resistance that has developed will automatically confer cross-resistance to all compounds in the same sub-group. It is this concept of cross-resistance within a family of chemically related insecticides or acaricides that is the basis of the IRAC MoA classification.
All effective insecticide resistance management (IRM) strategies seek to minimise the selection of resistance to any one type of insecticide. In practice, alternations, sequences or rotations of compounds from different MoA groups provide sustainable and effective IRM for insect and mite pests. This ensures that selection from compounds in the same MoA group is minimised, and resistance less likely to evolve.
Applications are often arranged into MoA spray windows or blocks that are defined by the stage of crop development together with the biology and phenology of the species of concern. Local expert advice should always be followed with regard to spray windows and timing. Several sprays may be possible within each spray window, but it is generally essential that successive generations of the pest are not treated with compounds from the same MoA group.
Resistance of insects and mites to insecticides and acaricides can result from enhanced metabolism by enzymes within the pest. Such metabolic resistance mechanisms are not linked to any specific site of action classification and therefore they may confer resistance to insecticides in more than one IRAC MoA group. Where such metabolic resistance has been characterized and the cross-resistance spectrum is known, it is possible that certain alternations, sequences or rotations of MoA groups cannot be used. Similarly, mechanisms of reduced penetration of the pesticide into the pest, or behavioural changes of the pest may also confer resistance to multiple MoA groups. Where such mechanisms are known to give cross-resistance between MoA groups, the use of insecticides should be modified appropriately.
The IRAC phone application and IRAC website is made available for the purposes of dissemination information. Details are accurate to the best of our knowledge but the information presented is subject to change. IRAC and its member companies cannot accept responsibility for how this information is used or interpreted. Professional advice should always be sought from local experts or advisors and health and safety recommendations followed.