Efficacy of fipronil-(S)-methoprene on fleas, flea egg collection, and flea egg development following transplantation of gravid fleas onto treated cats.

The goal of this study was to assess the insect growth regulator activity of the combination product fipronil-(S)-methoprene under a severe challenge model. Gravid fleas were allowed to feed on untreated donor cats for 48 hours before being transplanted onto untreated control cats and treated cats (treated once on day 0); 24 hours later, adult fleas were collected from all cats and counted to assess the 24-hour kill efficacy against the transplanted fleas, and flea eggs were collected and incubated to assess viability. The process was repeated weekly for 11 weeks. The 24-hour efficacy against transplanted adult fleas in the treated group was about 100% for the first 3 weeks and gradually declined to 93.4% by week 6. Egg production numbers were reduced on the treated cats compared with controls, with geometric mean egg counts on treated cats reduced from 76.9% to 96.3% during the initial 6 weeks of the study. The combination product was 100% ovicidal through day 56 and was still about 98% effective against eggs at the end of the study (day 76).