Observations on Males and Females of Sitophilus granarius (L.), the Granary Weevil, GG Strain, Exposed for Six Generations to Allethrin and Piperonyl Butoxide

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Abstract
In a recent discussion of the subject of insect resistance to insecticides, Brown (1958) has claimed that true resistance is characterized by a five-fold to ten-fold decrease in susceptibility. It is a genetic phenomenon arising as a result of selection. There is no evidence that insecticides are mutagenic, nor can resistance be induced by exposing insects to sublethal doses. A decrease in susceptibility that cannot be regarded as resistance is regarded as a condition of tolerance. In addition, the term “vigour tolerance”, intioduced by Hoskins and Gordon (see Brown, 1958) defines instances of enhanced tolerance due to extra vigour: true specific resistance is marked by a change of slope in the dosage-mortality regression line, while “vigour tolerance” is suggested if the regression line shifts but does not change in slope.

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