In vitro insecticidal effects of fipronil and beta-cyfluthrin on larvae ofthe blowfly Lucilia sericata

The insecticidal effects of the phenylpyrazole, fipronil, and a pyrethroid, beta-cyfluthrin, on larvae of the blowfly Lucilia sericata were determined in laboratory assays; When first stage larvae of L. sericata were reared o n homogenized pig liver which had been treated with known amounts of test; compounds, both fipronil and beta-cyfluthrin induced significant levels of mortality compared to acetone and water controls. However, fipronil was app roximately 10 times more toxic than beta-cyfluthrin to L. sericata larvae f ollowing ingestion. beta-cyfluthrin had little effect on mortality until co ncentrations of approximately 0.5 ppm were reached. In contrast, fipronil e ffected L. sericata mortality at a concentration of 0.05 ppm and 100% morta lity was reached by 0.5 ppm. The lethal concentration (LC50) value for beta -cyfluthrin was 1.56 ppm as compared to 0.14 ppm for fipronil, Following co ntact of first and third stage larvae with cloth impregnated with known amo unts of test compound, the mortality profiles of fipronil and beta-cyfluthr in were similar. At short contact times, the LC50 values for fipronil were lower than those for beta-cyfluthrin. However, at the highest contact time evaluated for the first stage larvae, 300 s, there was a reversal in this t rend. The results suggest that the phenylpyrazole fipronil may represent a new potential insecticide for development against blowfly strike of sheep. (C) 2000 Elsevier Science B.V. All rights reserved.