House rats (Rattus rattus) which do not consume a lethal dose of zinc phosphide develop poison-shyness after a single exposure. The surviving poison-shy rats cannot be baited again with zinc phosphide for about three months. Poison-shy rats were separately given anticoagulant baits (brodifacoum 0.005%, coumatetralyl and warfarin 0.025%) in no-choice tests. The first two anticoagulants were found to be the most efficient ones. It was observed that those R. rattus which had consumed 56.7 mg/kg or more zinc phosphide died sooner (P < 0.05 to 0.1) after anticoagulant poisoning when compared with normal rats. It is conjectured that prothrombin inhibition is accelerated in the liver of poison-shy R. rattus due to the action of phosphine present in the earlier ingested sublethal dose of zinc phosphide.

Control operations at 6-month intervals, continued for four years in crop fields, reduced the rodent population to 5.08 percent losses to agricultural production. After eight crop seasons, a significant reduction in rodent density was observed in treated areas when compared with that of the control areas (P < 0.01). Correlation between pre-treatment population index (y) and number of seasons (log of x) was found to be 0.91 (P< 0.01). A relationship was established between y and x: y = 0.804.0-0.9621 log x. From this equation, it can be inferred that rodent population will reach zero level after treating crop fields continuously for 6.85 or say 7 .0 (seven) seasons. After control, the numbers of predominant rodents, Tatera indica, Meriones hurrianae, and Rattus meltada, were significantly reduced and the residual population was composed of Mus booduga, Gerbillus spp., Rattus gleadowi, Golunda ellioti, and Funambulus pennanti.