Role of DDT-hydroxylation in Resistance

Abstract

To prove the rate of enzymatic detoxication in resistance, a direct correlation between the degree of insecticide resistance with the enzyme system concentration within the insect must be shown. Thus, in the housefly, DDT^* is readily converted to DDE by cell-free preparations and the resistance appears to be proportional to the DDT-dehydrochlorinase activity¹. DDT is also metabolized to a ‘Kelthane’-like material by a microsomal enzyme system, in several insect species, including Triatoma infestans^2,3. However, no significant data are available on the possible relation of DDT-hydroxylation to resistance. Correlation between the level of enzymatic detoxication and resistance can be shown by in vivo specific inhibition or stimulation of the enzymatic process, resulting in decreased or increased resistance, respectively. In this respect, it is known that SKF 525–A and other compounds, such as iproniazid, block microsomal hydroxylation reactions⁴, while 3-methylcholanthrene acts like an activator⁵. By using this last approach, it has been possible to show that the degree of tolerance to DDT by nymph T. infestans can be modified by the foregoing inhibitors and activators, suggesting that DDT-hydroxylation plays indeed a part in resistance.