Effects of Cypermethrin Selection on Expression of Insecticide Resistance Mechanisms in the German Cockroach (Blattaria: Blattellidae)

A cross-resistant strain of German cockroach, Blattella germanica (L.), (Marietta) expressing multiple resistance mechanisms was subjected to selection pressure with cypermethrin. Resistance to cypermethrin increased incrementally from 3.6-fold in the parental strain to 35-fold after 4 rounds of selection. No significant changes were observed in cytochrome P450 content, aldrin epoxidase activity, α-naphthyl acetate hydrolysis (cytosolic fraction), or glutathione S-transferase (CDNB conjugation) activities. Although no significant differences were observed in cypermethrin metabolism, a trend toward greater detoxification among each successive generation was observed. Furthermore, methoxyresorufin O-demethylase activity (often associated with pyrethroid resistance) increased incrementally with each successive selection iteration. The average knockdown time increased incrementally from 37 min (parental strain) to 177 min, and there was a corresponding increase in the kdr allele frequency from 19% to 99% after 4 rounds of selection. The data indicated that kdr-type nerve insensitivity and enhanced metabolism by cytochromes P450 and hydrolases were the principle mechanisms of resistance after selection with cypermethrin.

The Black-headed Gull's Adaptation to Polluted Environments: The Role of the Mixed-function Oxidase Detoxication System

This study was conducted to explore the role of the mixed-function oxidase (MFO) detoxication system in the ‘adaptation’ process of gulls to polluted environments. In two different populations of Black-headed Gull (Larus ridibundus), feeding in one case in a lagoon and in the other on an inland rubbish-dump, MFO hepatic activities (aldrin epoxidase, 7-ethoxyresorufin o-deethylase, NADPH-cytochrome c reductase, NADH-cytochrome c reductase, and NADH-ferrycianide reductase) and chlorinated hydrocarbon residues were determined. All the enzymatic activities detected, and the PCB residues, were higher in the Gulls feeding on the inland dump than in the gulls feeding in the lagoon.The results obtained suggest that the development of a strong detoxication system constitutes an important ‘survival mechanism’ for these birds when feeding customarily in polluted environments.

Aldrin epoxidase activity in liver microsomes from normal or streptozotocin-diabetic rats: Comparison with activity in isolated hepatocytes from normal rats incubated with glucagon

Aldrin epoxidase activity in liver microsomes from streptozotocin-diabetic rats is only 40% of that from normal rats. Epoxidation of aldrin has also been assayed in freshly isolated hepatocytes from normal rats. Addition of 10−7 M glucagon to the incubation medium leads to a decreased aldrin epoxidase activity. Owing to the previously reported phosphorylation of a purified cytochrome P-450 isozyme, it is postulated that the cytochrome P-450 dependent aldrin epoxidase may be regulated by a glucagon induced phosphorylation process.