Duration of Fipronil and Imidacloprid Gel Baits Toxicity against Blattella germanica Strains of Iran

The current study was conducted to investigate the duration of fipronil and imidacloprid gel baits toxicity against Ger-man cockroach strains in Iran during 2003-2004. In order to conduct this study, nine German cockroach strains were used. Newly emerged adult male German cockroaches starved for one scotophase (12 h), and ingested fipronil and imidacloprid gel baits for 2 h. After the given time was over, the bait was removed and replaced with mouse pellet. Mortality was re-corded at 12 intervals for 144 h (6 days). Mortality data of the replicates were pooled and was tested using probit analysis. Both gel baits were toxic to adult male German cockroaches. In the ingested bait method, the susceptible strain showed LT50 of 47.1 and 11.3 h for fipronil and imidacloprid gel baits, respectively, and the average LT90 was 74.2 and 19.3 h, respec¬tively. LT50 of the feral German cockroach strains varied 14.9 h from 30.5 to 45.4 h and 4.4 h from 12.4 to 16.8 h for fipronil and imidacloprid gel baits, respectively. All German cockroach strains showed a similar susceptibility to fipronil and imidacloprid gel baits, compared with the susceptible laboratory strain. The steep slopes of ingested bait mortality curves indicated that the feral German cockroach strains were homogenous to fipronil and imidacloprid ingested gel baits. These results suggest that fipronil and imidacloprid gel baits appear to have considerable potential as a bait for insecticide-resistant strains of German cockroach.