Variation in mortality among populations is higher for pymetrozine than for imidacloprid and spiromesifen in Trialeurodes vaporariorum in greenhouses in Finland

Abstract

Abstract. BACKGROUND: Insecticide resistance in Trialeurodes vaporariorum W. is unknown in the species’ northern distribution range where it inhabits mainly commercial greenhouses. Resistance development in whiteflies feeding on year-round crops in greenhouses is possible due to use of chemical treatments to back up biocontrol. We tested the response levels to spiromesifen, pymetrozine and imidacloprid in whiteflies collected from seven greenhouses within a 35 km radius in Western Finland. RESULTS: All except one (PR) population had LC50 values below the recommended concentrations for the tested compounds. However, some populations showed reduced susceptibility to pymetrozine in comparison to reference susceptible population. Resistance ratios to pymetrozine were highly variable (RR 0.5-39.7) even among closely-located greenhouses and higher than those for imidacloprid (RR 1.05-10.5) and spiromesifen (RR 0.8-11.5). LC50 values and application frequencies of pymetrozine correlated positively among the sampled populations. CONCLUSION: High variation in resistance levels to pymetrozine among populations within natural whitefly dispersal limits reflects variation in the usage of this compound among individual greenhouse crop producers. Thus, resistance management is recommended on individual greenhouse crop producer level, even in a dense production cluster.