Submitted to: Recent Research Developments in Entomology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/16/1996
Publication Date: N/A
Citation: Interpretive Summary: Prior work had demonstrated that younger stages of the German cockroach were more tolerant to various insecticides than adults. Pest control operators had also found that after insecticide applications, young German cockroaches seemed to survive the treatments better than adults (i.e. they were unable to kill younger stages). This phenomenon prevents effective control of German cockroaches. Scientists at the USDA, Agricultural Research Service, Center for Medical, Agricultural and Veterinary Entomology in Gainesville, Florida, identified the biochemical mechanisms responsible for this stage-dependent insecticide tolerance. Specifically, they showed that younger German cockroaches metabolize insecticide faster than adults. In addition, younger German cockroaches possess more detoxification enzymes than adults. Thus, they were able to make younger German cockroaches as susceptible as adults to insecticides with the addition of an insecticide synergist such as piperonyl butoxide. Therefore, these recommendations will reduce insecticide load in the urban environment by making them more effective and prevent unnecessary insecticide applications.
Technical Abstract: Differential insecticide susceptibility between developmental stages of the German cockroach was evaluated. Late-stage nymphs were consistently identified as the most tolerant developmental stage, reaching tolerance levels of up to 27-fold greater than adult males. Biochemical mechanisms responsible for conferring enhanced nymphal tolerance toward the carbamate insecticide, propoxur, were elucidated. Final instar male nymphs (mid-stadium) were 15-fold more tolerant of propoxur than adult males. Nymphal tolerance was reduced to 2-fold with piperonyl butoxide pretreatment. Final instar nymphs oxidatively metabolized propoxur (in vitro) 3-fold faster than adult males. Methoxyresorufin O-demethylase and ethoxyresorufin O-deethylase activities were significantly greater in final instar nymphs, as was total cytochrome P450 content. Altered acetylcholinesterase and decreased cuticular penetration did not contribute to the enhanced nymphal tolerance to propoxur. Therefore, the major mechanism of tolerance was attributed to the enhanced oxidative detoxification capacity of the nymphs. Further studies examined the tissue localization and developmental expression of cytochrome P450 monooxygenases in final instar nymphs and adult males.