Insecticide Resistance Strategy

Combating resistance remains a significant challenge:  the loss of a single compound or an entire pesticide group (through a shared resistance mechanism) can threaten the productivity and competitiveness of an agricultural system.

Attempts to predict and forestall resistance encounter two challenges. Firstly, the need to take account of the very large number of factors (‘traits’) that can potentially influence whether resistance occurs, and the speed at which it is selected. Secondly, it is usually very difficult to perform experiments to unravel these interactions or compare the outcome of alternative resistance management tactics in the field. To address this problem a modelling approach was used to compare the effectiveness of resistance management strategies for delaying the development of target-site resistance for groups of pest species sharing similar traits.

The conclusions were that in most scenarios tested, a higher dose of insecticide leads to faster selection for resistance resulting from a single target-site mutation.

The combination of two insecticides with different modes of action (MoA), to which resistance from two target-site mutations (one for each MoA) was developing, was also evaluated. The modelling approach indicated that when two insecticides were applied together at their label dose in a mixture, resistance developed considerably faster than when the two insecticides were alternated.

However, if the dose of each insecticide was reduced so that the mixture provided the same control of the insect population as a single label dose of either product alone, then mixtures were often the most effective resistance management tactic. Only when the resistance resulted in substantial fitness costs in the insect species did alternating two insecticides at their label dose lead to slower resistance development than reduced-dose mixtures.

The project final report can be accessed here

The findings from the project will be considered by the Insecticide Resistance Action Group (IRAG) and resistance management strategies adapted accordingly.

Regular monitoring of key pests for evidence of insecticide resistance is carried out by a team at Rothamsted with funding from AHDB and agrochemical and agronomy businesses and BBRO. Results from the project can be accessed here and are used to update the IRAG guidance documents.