["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 owing to the use of chemical treatments to back up biocontrol. The authors tested the response levels to spiromesifen, pymetrozine and imidacloprid in whiteflies collected from seven greenhouses within a 35\u2009km radius in western Finland.", '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 with the reference susceptible population. Resistance ratios to pymetrozine were highly variable (resistance ratio 0.5-39.7), even among closely located greenhouses, and higher than those for imidacloprid (resistance ratio 1.05-10.5) and spiromesifen (resistance ratio 0.8-11.5). LC50 values and application frequencies of pymetrozine correlated positively among the sampled populations.'] Is variation in mortality among populations higher for pymetrozine than for imidacloprid and spiromesifen in Trialeurodes vaporariorum in greenhouses in Finland?