To illustrate what can be achieved in this area, we now consider two studies in more detail. In a classic study of insecticide detoxication in the aphid yzus persidae, Devonshire and Sawicki (1979) used strains that differed in their insecticide resistance. The strains were genetically different, and the mortality and growth rates of each strain were examined in a standard environment. More resistant strains con tained more detoxifying enzyme (phosphatase Ei, up to 1% of total protein) because they contained more duplications of a structural gene (figure 8.16A). LD os were measured for three of these strains, from which mortality rates could be obtained (figure 8.16B). Note that strains containing more copies of the structural gene, which presumably spent more on detoxication, achieved a reduction in mortality rate.