A review of the interactions between multiple insecticide resistance loci

Insecticide resistance is an ever escalating problem worldwide in many pest populations and numerous cases of insecticide resistance are polygenic. Therefore, it is important to investigate the types of interactions that occur between insecticide resistance loci as this will dictate the level of resistance (and effectiveness of a chemical control strategy). Interactions also play a role in the evolution and/or maintenance of multigenic resistance in the field. Given that a limited number of mechanisms confer resistance, it might be possible to establish general rules for interactions between mechanisms. Several variables might dictate the type of interaction, such as the nature of the resistance mechanisms, genotype, etc. Interactions can be synergistic, antagonistic or additive. Based on this literature review, the most common interaction of multiple homozygous resistance loci is synergistic and additive when loci are heterozygous. When one locus is homozygous and the other locus is heterozygous the most common interaction was synergistic, although very few studies have examined this type of interaction. Possible factors that drive these interactions, exceptions to the trends, and future research needs are discussed.