SELECTION FOR DDT TOLERANCE IN A BENEFICIAL PARASITE, MACROCENTRUS ANCYLIVORUS ROH.: I. SOME SURVIVAL CHARACTERISTICS AND THE DDT RESISTANCE OF THE ORIGINAL LABORATORY STOCK

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Abstract
Macrocentrus ancylivorus Roh. is a short-lived insect, a fact which must be taken into account in any experimental work on this species. Well fed females have a mean life of about five days. In the absence of food, but in the presence of water, this period is reduced to one and one-half days. In the absence of water and in dry air it is not much further decreased; adequate nutrition seems to be the main survival factor. Exposure of young adults to films of crystalline DDT in celloidin, for a few minutes, results in a heavy initial mortality with the toxic action completed within 40 hr., subsequent deaths being due to natural mortality. In all experiments males were more susceptible than females. In view of the short life of the insect, the results can be conveniently expressed in survival, or longevity, curves; these show the quantitative effects of the DDT in destroying part of, and in affecting the natural decline of, the experimental populations. Examination of the death rate among the tail of survivors of such DDT treatments shows that destruction has been selective, and that these insects die more slowly than those in the controls.