Induction of detoxication enzymes in insects.

Most of the known enzyme systems involved in the degradation of insecticides, other xenobiotics, and hormones of insects, appear to be inducible by various dietary chemicals, both plant-based and man-made. Although the understanding of the mechanism of this phenomenon comes almost entirely from studies of higher animals, there are good reasons to believe that the insect system is similar in most respects. If so, it involves a recognition system wherein exogenous chemicals in the insect's environment can stimulate the production of the enzymes that degrade them. Evidence is presented that some plant species and some plant allelochemicals are capable of such enhancement and that this is sufficient to increase the tolerance of an insect to various insecticides. It is also suggested that induction by plant chemicals may be involved in the insect's adaptation to its plant diet. Further understanding of the phenomenon, especially in regard to the cyclic nature of the process in plants and insects, may be of value in organizing pest management programs.

Abnormalities in the microsomal oxidases of the WHO standard reference strain of Musca domestica.

Observations made during biochemical and toxicological studies of the housefly, in which the WHO standard reference (SR) strain was used as a standard, indicated that this strain differs from other strains in certain physiological and toxicological aspects. Experiments are described in which microsomal oxidases prepared from the standard reference strain and several other housefly strains, both susceptible and resistant to insecticides, were compared for heat stability, sensitivity to ionic strength, pH optima, and the spectral characteristics of their cytochrome P-450. In a comparison with 8 strains the SR strain microsomes were more stable at high incubation temperatures (40-47.5 degrees C). Compared to two other strains (NAIDM, susceptible, and Isolan-B, resistant) SR was more stable at low pH and more sensitive to high ionic strength. In spectral comparisons with NAIDM and Isolan-B, SR was found to contain microsomal cytochrome P-450 that differed slightly in its carbon monoxide or octylamine binding spectra. The results suggest that this strain may not provide a suitable reference in studies involving the microsomal oxidases. However, these apparent differences should not reduce the value of the SR stain as a reference in insecticide resistance studies.

Induction of microsomal oxidase in F1 hybrids of a high and a low oxidase housefly strain.

Microsomal oxidase activity is increased up to sixfold in dieldrin-resistant houseflies exposed to sublethal doses of dieldrin. The net increase in enzyme activity is greater in a strain initially high in oxidase activity than in a strain low in this respect, and this tendency is carried into the F(1) hybrids of the strains.