Chlorinated Hydrocarbon Resistant Northern Corn Rootworm in Wisconsin1

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Abstract
The first evidence in Wisconsin of chlorinated hydrocarbon resistance in the northern corn rootworm, Diabrolica longicornis (Say), occurred in 1963. This phenomenon appeared after the use of aldrin at the rate of ½ to 1 lb per acre in starter-fertilizer during 8 of 10 years (1954-63). Beetles from this field showed a 228-fold resistance to aldrin in 1963. Adults collected at random from 6 fields in southern Wsiconsin during the same year were classified as susceptible with LD50s ranging from 0.03 to 0.13μg of aldrin per beetle. Beetles from farms in the neighborhood of the first problem field were tested in the laboratory during 1964. No evidence of dispersion was noted west of the problem field, but definite movement to a farm on the south was detected. Numerous complaints of rootworm control failure were received in 1965. Beetles from 4 such fields had LD50s ranging from 15.5 to 20.7 μg per beetle. These evidences of high resistance occurred in fields where aldrin or heptachlor had been used for 8 to 11 years. Response of beetles to diazinon was the same whether beetles were resistant to aldrin or not. The 2 hour LD50s for this insecticide ranged from 0.23 to 0.35 μg per beetle.