Hydroxylation as a Factor in Resistance in House Flies and Blow Flies1

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Abstract
The hydroxylation of napthalene by microsomes prepared from the house fly, Musca domeatica L., and the black blow fly, Phormia regina (Meigen), has been measured in search of differences related to sex, age, insecticide susceptibility, and species. The results of these tests have been compared further with those obtained when the 2 species were exposed to naphthalene vapors. Correlation between in vitro hydroxylation and in vivo resistance has been found. P. regina is more susceptible to naphthalene vapors than M. domestica, while microsomes from P. regina are only 1/3 as active in the hydroxylation of naphthalene as those prepared from M. domestica. Older house flies contain microsomes of greater hydroxylating capacity than younger insects. House flies highly resistant to DDT and dieldrin are approximately twice as active in the in vitro hydroxylation of naphthalene as a strain only moderately resistant to these insecticides. A house fly strain, selected for resistance to naphthalene, is shown to have a correspondingly high capacity to hydroxylate naphthalene in vitro.