SOME ASPECTS OF RESPIRATORY METABOLISM DURING METAMORPHOSIS OF NORMAL AND DDT-RESISTANT HOUSE FLIES, MUSCA DOMESTICA L

¹ Chemical Corps Medical Laboratories, Army Chemical Center, Maryland

1. Oxygen consumption follows a U-shaped curve during metamorphosis of normal and DDT-resistant strains of house flies. It is of the same order of magnitude in both strains.

2. Cytochrome oxidase activity during metamorphosis also follows a U-shaped curve. There is evidence that changes in oxygen consumption during this process are, in some respects, related to the activity of the oxidase.

3. A cyanide insensitive system, possibly flavin, and another cyanide sensitive system, probably tyrosinase, contribute to the total oxygen consumption. The latter system apparently contributes mainly during the early stages of metamorphosis.

4. The cyanide insensitive respiration of both strains remains relatively constant throughout development. The resistant strain has twice the cyanide insensitive respiration of the normal strain.

5. The DDT-resistant pupae have less cytochrome oxidase activity than normal pupae at all stages except immediately prior to emergence of the adult.

6. The pupae of DDT-resistant flies exhibit resistance to cyanide.

7. The effects of cyanide vary, depending on the developmental stage of the pupae. A given concentration of the inhibitor produces different degrees of inhibition and mortality in pupae of different age. One of the possible explanations may be a change in the substrate being metabolized. Other possibilities are mentioned.

8. The possible mechanisms of resistance of pupae to cyanide are discussed. These may be: (a) a by-pass of the cytochrome system; (b) a difference in reversibility of enzyme-inhibitor complex or; (c) a detoxification of inhibitor. It is suggested that DDT-resistance may depend, in part, on similar factors.

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