Synergism and Antagonism in the Analysis of Insecticide Resistance

This review discusses the calculation of paramaters expressing synergism or antagonism of insecticide lethality, using examples of insecticide-resistant insects. Calculations of “percent synergism” (%S), “log-percent synergism” (L%S), and “relative percent synergism” (R%S) express hypotheses generated from biological assay data better than does the more usually cited synergist ratio. The calculations are discussed relative to detecting potentiation between resistance mechanisms, kdr gene effects, and enhanced metabolism. The LD 50 values with (sLD) or without (LD) synergism in susceptible (S) or resistant (R) strains are used as their logarithms (also LD + 1) in the following relationships describing synergism: L%S = 100[(LD + 1) − (sLD + 1)]/(LD + 1); R%S(R) = 100[LD(R) − sLD(R)]/[LD(R) − sLD(S)]; and R%S(S) = 100[LD(S) − sLD(S)]/[LD(R) / sLD(S)]. The %S is 100 [LD — sLD]/LD, but the LD 50 values are not used as their logarithms.