Susceptibility of the roof rat, Rattus rattus, captured in several places to warfarin and scilliroside

Abstract

Warfarin and scilliroside were administered orally to the wild roof rat, Rattus rattus, captured in Tokunoshima Island where the control with rodenticides was considered to have been scarcely done. Ten days' administration of warfarin resulted in LD50 of 35mg/kg and single administration of scilliroside resulted in that of 1.2mg/kg, suggesting the susceptible level to these chemicals of this species in Japan. On the other hand, the roof rats captured at several buildings in Tokyo where it has been difficult to control the species with these chemicals, were allowed to feed 0.025% warfarin powdered bait. One of the rats captured at Shinjuku survived for more than 70 days, suggesting that resistance to this rodenticide has developed in the urban area.