Submitted to: Pesticide Biochemistry and Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 4, 2001
Publication Date: N/A
Interpretive Summary: Insecticide resistance has been estimated to cost $133 million annually in the U.S. and perhaps $1 billion worldwide. The German cockroach has developed resistance to all of the traditional insecticides and cross resistance has been reported among many new insecticides. Elucidation of the biochemical and molecular mechanisms responsible for insecticide resistance in the German cockroach may provide new methods to prevent or delay its development. Scientists at the Center for Medical, Agricultural and Veterinary Entomology in Gainesville, Florida have identified a key mechanism responsible for cypermethrin resistance in the German cockroach, a variant of an enzyme an esterase isozyme. The esterase was purified and indeed found to metabolize cypermethrin faster in the resistant strain. This unique isozyme may provide a method to detect cypermethrin resistance in field strains of the German cockroach which would ultimately reduce insecticide use and improve control effectiveness.
Technical Abstract: Adult male German cockroaches of the Marietta strain exhibited a 5-fold level of resistance to cypermethrin compared with the insecticide susceptible Orlando strain. The cypermethrin resistance level decreased to 2.9-fold when cockroaches were pretreated with DEF indicating that esterases played a role in the resistance. Cypermethrin was metabolized faster by microsomal esterases from the Marietta strain (15.4 ñ1.1 pmol/h/mg) compared with Orlando (12.5 ñ0.2 pmol/h/mg). Partial purification of microsomal esterases from the Marietta and Orlando strains was accomplished by anion exchange and hydrophobic interaction chromatography (HIC) and native-PAGE. HIC partitioned the single anion exchange peak of à-naphthyl acetate esterase activity into 3 fractions, HIC I, HIC II, and HIC III. All three HIC fractions metabolized cypermethrin significantly faster than microsomes. Native PAGE analysis of each of these efractions revealed a unique band in Marietta HIC II and III. The unique esterase in Marietta, referred to as Microsomal Esterase Marietta (MEmar), was isolated by native-PAGE and found to hydrolyze à-naphthyl acetate at a rate of 25.5 æmol/min/mg protein, representing a purification of 54-fold over microsomes. Furthermore, Marietta strain HIC II and III fractions (which contained MEmar) metabolized cypermethrin significantly faster than the corresponding fractions from the Orlando strain. MEmar metabolized cypermethrin at 3,461 pmol/min/mg protein, representing a 225-fold increase over microsomes. MEmar was found to exhibit a molecular weight of 57 kDa by SDS-PAGE and 64 kDa by gel filtration chromatography indicating that the esterase was a monomer. Also, the MEmar isozyme was inhibited by paraoxon and PMSF indicating that the esterase was a "B" type serine esterase.