CHANGES IN RESISTANCE TO DDT IN MACROCENTRUS ANCYLIVORUS ROHW. (HYMENOPTERA: BRACONIDAE)

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Abstract
Exposure of the arrhenotokous parasite Macrocentrus ancylivorus Rohw. to 23 μg./cm.2 of DDT for 3 minutes in each of 10 successive generations increased the level of resistance to four times that of the original stock. When the concentration of DDT was increased to 96 μg./cm.2 of DDT for 3 minutes from the F11 generation on, the resistance reached a maximum of 12 times that of the initial stock at the F19 generation, and at the F29 generation was nine times the original level. In the F30 to F71 generations, when only females were exposed to DDT, the level of resistance fell to seven times its initial value. When, beginning with the F72 generation, the parasite was reared for 13 generations without exposure to DDT, resistance fell to its initial level. Females were more DDT-resistant than males.