Effect of warfarin and diphacinone baits to a warfarin-resistant colony of Rattus rattus

Abstract

The following information was obtained after feeding a warfarin-resistant colony (RR : 50%) of Rattus rattus with bait containing various concentrations of warfarin or diphacinone. 1. High lethal effect was obtained in a comparatively short period by higher concentrations of warfarin, 0.25 or 0.5%, though the rats are resistant to 0.025% warfarin bait. 2. The warfarin-resistant colony showed cross resistance to diphacinone. 3. The log day-probit mortality curve of the colony after feeding with 0.005% diphacinone formed a curve with one plateau. The RR ratio to diphacinone was estimated from the plateau to be around 25%, which was lower than the RR ratio to warfarin (50%). 4. The rats given diphacinone bait of higher concentrations, 0.015 or 0.025%, all died in a comparatively short period, thus showing no resistance to diphacinone. 5. The potency of bait with 0.025% warfarin seemed equivalent to that of bait with 0.005% diphacinone.