The major problem in the chemical control of arthropods of medical importance continues to be the development of resistance by these arthropods to the pesticides commonly employed against them. Each year the problem becomes more critical through an increase in (a) the number of resistant species, (b) the areas wherein the given species are resistant, and (c) the types of insecticides to which the species are resistant. Previous workers (Hess, 1952, 1953; Simmons, 1954; Pinotti, 1954; Brown, 1954) have discussed the general picture and significance of resistance in insects of public health importance. In this paper the present status of resistance will be considered with emphasis on the evaluation of the currently available experimental evidence for the confirmation of reported cases of resistance.
For the purpose of this discussion, resistance is defined as the ability of an arthropod population to survive exposure to dosages of a toxicant to which it formerly was highly susceptible.