2003 Volume 18 Issue 1 Pages 1-6
Influence of the population density and feeding behavior of Blattella germanica on the lethal effect of toxic baits containing fipronil was evaluated in laboratory. Firstly, to determine the oral toxicity of fipronil, susceptibility of 2 strains of B. germanica, an insecticide-susceptible strain (Watarida) and a field-collected strain (Osanbashi), was estimated by oral administration. The Osanbashi whose LD50 was 6.99ng/♀, was 1.8 times more tolerant compared with the Watarida whose LD50 was 3.96ng/♀. Secondly, the influence of population density on the lethal efffect of the bait was examined. A hundred percent mortality was obtained by day 11 after placement of 6 or 12 spots of 30mg-bait for ca. 100 cockroaches (1.68 or 3.55mg bait/cockroach, respectively). The mortality due to the bait depended upon the amount of bait treated/cockroach. Furthermore, the lethal effect of 0.05% fipronil bait was compared with that of 0.03% fipronil bait. Both baits for 2 strains of B. germanica exibited >99% mortalities by day 2, except the 0.03% bait for the Osanbashi which gave only 60% mortality. The mortality of the Osanbashi by 0.03% bait was less than that by 0.05% bait. And bait consumption of the Osanbashi obserbed in 0.03% bait was less than a half amount in 0.05% bait. Consequently, an aversion of the Osanbashi to 0.03% bait was considered as a factor which caused the low mortality.
