DDT-Resistance of the Colorado Potato Beetle1

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Abstract
Field observations in the Red River Valley of Minnesota and North Dakota indicated some resistance of the Colorado potato beetle (Leptinotarsa decemlineata (Say)) to DDT as early as 1952 and 1953. This indication of resistance has been supported by determining the toxicity levels of injected DDT to adult beetles collected from two widely separated areas. Beetles were taken from the Red River Valley where resistance is apparent and from Belleville, Ontario, Canada where no DDT or chlorinated hydrocarbons have been used. The Minnesota beetles tolerated large doses of DDT. The LD-50 value was greater than 3000 micrograms per gram of body weight. The Canadian beetles were more susceptible, and the LD-50 values were 322 and 435 micrograms per gram for males and females, respectively. Since Dimite used in combination with DDT did not produce any detectable difference from DDT used alone, the results did not provide any due as to the mechanism of the resistance.