Abstract
The development of strains or races of insects that are resistant to insecticides is a serious obstacle to the progress of chemical pest control. In many cases recommendations at first viewed as offering a permanent solution for an entomological problem have had to be abandoned within a very few years. Until the general relationships governing insccticidnl resistance are reduced to an orderly and understandable basis, the permanent soIution nf an insect pest control problem by chemical treatment is largelv an unjustifiable expectation.