Comparative efficacy of two methods of delivering an anticoagulant rodenticide to three species of South Asian rodents

The efficacy of two methods, namely contact poisoning (during which animals ingest poison during grooming of fur and feet) and poison baiting (during which animals ingest poison during feeding), of delivering a rodenticide, Racumin (coumatetralyl), to three species of South Asian rodents, Bandicota bengalensis, Tatera indica and Rattus rattus, was determined in laboratory and field experiments. Species-specific differences occurred between the efficacy of 0.75% Racumin tracking powder (RTP) used for contact poisoning, and 0.0187, 0.0375 and 0.075% Racumin baits (RB), prepared by mixing the concentrate with cracked wheat, powdered sugar and peanut oil (96:2:2), used for poison baiting. B. bengalensis was most susceptible to the toxic effects of Racumin as both RTP and RB caused 80–100% mortality after short exposures (15 min and 3 h) to a floor/runway treated with 1 g/rat of RTP in forced contact and simulated runway techniques and 1–2 days of choice feeding of 0.0187 and 0.0375% RB in feeding tests. These treatments were less effective against T. indica and least effective against R. rattus. In pen experiments, in which the runway was treated with 2g of RTP, 100 and 60% mortality from groups of 5 rats each of B. bengalensis and T. indica occurred, respectively.