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There are a number of definitions of control of a pest. One of the competing definitions, and probably the most common even if not accepted in advanced circles, is to kill off the pest. Translated, this says: to increase the mortality rate, preferably to an extreme degree. I am going to talk here about survival rates. A survival rate is just the complement of the mortality rate - if survival is 80 percent, then mortality is 20 percent. It happens to be more generally useful in studying populations to deal with survival rates, so I hope I may be excused not having translated everything to mortality rates as I might have done. All animals are mortal, so left to themselves their populations would dwindle to nothing except for their rates of reproduction. It is necessary to know what the natural rates of survival are in order to avoid confusing the natural decline of populations during periods of low reproduction with the supposed effect of some control measure. The trials described here are simple in concept. We have measured survival both with and without control measures with the primary purpose of comparing rates under the two conditions and then judging the efficacy of treatment from the changes in survival rates.