Rearing and Treating Successive Generations of Boll Weevils

In studies of boll weevil ( Anthonomus grandis Boh.) resistance to chlorinated hydrocarbon insecticides, 10 generations were reared from September 1956 to September 1958 and 4 to 6 generations were treated topically with insecticides. There was no indication of reversion to susceptibility in the untreated strains when tested with endrin. Endrin applied to resistant and susceptible strains increased the LD-50 and LD-90, and gave some changes in slope of lines. A mixture of equal parts of endrin and Gut ion® ( O,O -diethyl S -(4-oxo-3 H -1,2,3-benzotriazine-3-methyl) phosphorodithioate) and Gut ion alone gave no changes in LD-50, LD-90, or slope. However, this does not prove that resistance will not develop with continued selection in large populations of boll weevils.