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Submitted to: Journal of Entomological Science
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 6/18/2003 Publication Date: 4/5/2004 Citation: Valles, S. M. 2004. Effects of Cypermethrin Selection on Expression of Insecticide Resistance Mechanisms in the German Cockroach (Blattaria: Blattellidae). Journal of Entomological Science. v. 39(1). p.84-93. Interpretive Summary: Insecticide resistance has been estimated to cost Americans $133 million annually 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. In an effort to understand the biochemical and molecular mechanisms responsible for insecticide resistance in the German cockroach, a scientist at the Center for Medical, Agricultural and Veterinary Entomology in Gainesville, Florida, exposed a population of German cockroaches to a widely used insecticide over several generations and followed the development of resistance. Several resistance mechanisms (including enhanced detoxification and target site insensitivity) were found to be expressed in the selected population. These data strongly indicate that multiple resistance (many mechanisms expressed simultaneously) is an inherent characteristic of the German cockroach and treatments will have to be tailored to achieve effective control. Technical Abstract: A cross resistant strain of German cockroach (Marietta) expressing multiple resistance mechanisms was subjected to intense cypermethrin selection pressure. Resistance to cypermethrin increased incrementally from 3.6-fold in the parental strain to 35-fold after 4 rounds of selection. Piperonyl butoxide (PBO) and S,S,S-tributyl phosphorotrithioate (DEF) had a diminished synergistic effect on each successive population. No significant changes were observed in cytochrome P450 content, aldrin epoxidase activity, -naphthyl acetate hydrolysis (cytosolic fraction), or glutatione S-transferase (CDNB conjugation) activities. Similarly, no significant differences were observed in cypermethrin metabolism by microsomal monooxygenases or hydrolases in the microsomal and cytosolic fractions. Conversely, methoxyresorufin O-demethylase activity 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. Although the data indicated that kdr-type resistance was the primary mechanism being selected, metabolic components (cytochromes P450 and hydrolases) continued to play a role in the overall resistance level. |
