Proceedings of the Vertebrate Pest Conference

The use of warfarin in commensal rodenticides has been avoided by the pest control industry for many years because of concerns with low palatability, resistance, and its chronic toxicity requirements. It has been all but forgotten by the industry. Genesis Laboratories, Inc. evaluated warfarin in a currently-marketed commensal rodenticide, Kaput Rat and Mouse Bait (0.025% warfarin), in comparison to Maki pellets (0.005% bromadiolone) and Talon G pellets (0.005% brodifacoum) in a simulated field study design using warfarin-resistant wild Norway rats. Approximately 20 wild rats of varying ages and weights were randomly added to each of 3 study rooms, one for each product. After a 7-day acclimation period, the respective rodenticide baits were presented to the rats along with the EPA field rodent challenge diet or another alternate diet. The first death in each study room was recorded on Day 3 for Kaput, Day 13 for Maki, and Day 5 for Talon. Kaput acceptance was high, causing 9 deaths in the first 14 days. Again, because of poor acceptance of the Maki and Talon baits, the alternate diet was changed to milo on Day 22 and again to a no-choice regime on Day 28. At this point (Day 28), efficacy of the Kaput, Maki, and Talon rooms were at 85%, 20%, and 10%, respectively. 100% efficacy was achieved on Day 36 by Kaput, Day 38 by Maki, and Day 42 by Talon during the no-choice phase of the study. To investigate the warfarin toxicology profile further, we initiated another study with laboratory Norway rats and house mice in a no-choice regime with varying exposure periods (1, 2, 3, 4, and 5 days). At least two days of exposure was required to produce 100% mortality with the rats and 5 days of exposure was necessary for 100% mortality of house mice.