The susceptibility to insecticides of laboratory cultures of an insect species

Adult Calandra of the same age but some reared from a wild strain and the others from a laboratory strain were used in tests with pyrethrins powders. The laboratory strain was found to be between three and a half and six and a half times as susceptible to pyrethrins as the wild strain, which was not appreciably less susceptible to synergized pyrethrins (pyrethrins and piperonyl butoxide) than was the laboratory strain. Several strains of adult Tribolium of the same age showed differences in susceptibility to γ‐BHC, pyrethrins and, to a lesser degree, to synergized pyrethrins. These strains were developed from cultures from different laboratories. γ‐BHC was found to be four times, and pyrethrins three and a half times, more effective against the most susceptible strain of Tribolium than against the least susceptible strain. Differences in susceptibility are believed to be due to differences in vigour.