Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/17/1997
Publication Date: N/A
Citation: Interpretive Summary: Insecticide resistant German cockroach populations maintain the need for the development of new pesticides to provide control. Scientists at the Center for Medical, Agricultural and Veterinary Entomology, USDA-ARS and the University of Florida evaluated the effectiveness of a new pesticide (fipronil) against the German cockroach. Fipronil effectively killed laboratory-reared German cockroaches when applied in nanogram quantities. Unfortunately, field-collected strains were significantly more tolerant of fipronil than the laboratory strains suggesting that an insecticide resistance mechanism may already be present in German cockroach field populations. Furthermore, it was determined that German cockroaches metabolically activate (make more toxic) fipronil in their bodies. The apparent cross resistance exhibited by field populations toward fipronil question its long-term utility for use against German cockroaches.
Technical Abstract: Toxicity of the phenylpyrazole insecticide, fipronil, was determined in laboratory and field strains of the German cockroach, Blattella germanica (L.). Fipronil effectively killed German cockroaches when applied in nanogram quantities. Orlando (insecticide-susceptible), HRDC (carbamate and organophosphorus resistant), and Village Green (pyrethroid resistant) strains were equally susceptible to fipronil with LD50 values between 4.6 and 5 ng/insect. The Marietta strain (pyrethroid, organophosphorus, and carbamate resistant) was 1.6-fold more tolerant of fipronil compared with the Orlando susceptible strain. Five German cockroach strains collected from the field were considerably more tolerant of fipronil than Marietta cockroaches. Piperonyl butoxide (PBO) and S,S,S-tributyl phosphorotrithioate (DEF) strongly antagonized the toxicity of fipronil in all strains evaluated. Fipronil was 2.2 to 3-fold less toxic when cockroaches were pretreated with PBO or DEF as compared with fipronil alone. These data suggest that fipronil is metabolically activated in German cockroaches possibly via sulfone formation catalyzed by microsomal oxidases.