RODENTICIDAL ACTIVITY OF BROMADIOLONEâ•flA NEW ANTICOAGULANT

Bromadiolone, a new anticoagulant rodenticide, has been evaluated against laboratory rats and mice. Kill of both species was excellent, even when bromadiolone was offered for only one day in the presence of alternative food. Effectiveness against homozygous warfarin resistant rats was also demonstrated. Limited field trials on farms showed that after baiting for seven days with bromadiolone, warfarin resistant rat populations were substantially reduced although subsequent re-infestation occurred. Longer or continuous periods of baiting with bromadiolone would almost certainly prevent population increase, but government restrictions on the amount of bait approved for the trials did not allow this to be demonstrated. INTRODUCTION The introduction of anticoagulants stands out as the major development in rodent control in the last twenty-five years. But in 1958, a population of Rattus norvegicus, in Scotland, became resistant to the most commonly used anticoagulant, warfarin (Boyle 1960) a problem which was subsequently recognized in other parts of Britain. Since then anticoagulant resistance has been found in a number of rodent species in various parts of the world, including the U.S.A. This has been well-documented and Kaukeinen (1977) has produced an extensive bibliography. Generally there has been cross-resistance, to a greater or lesser degree, to all of the more established anticoagulants. Recently, however, new anticoagulants with the ability to control these resistant animals have been synthesized. The first to be marketed was difenacoum and Bull (1976) has reviewed the properties of this anticoagulant. More recently, Rennison and Dubock (1978) have field tested brodifacoum, an analogue of difenacoum. Bromadiolone, is another similar type compound, which is also capable of controlling warfarin resistant rats and mice. Marsh (1976) and Grand (1976) have shown that bromadiolone has activity against a wide range of rodents, including gophers, ground squirrels, various "field" mice and voles. Bromadiolone is a hydroxy coumarin with the full chemical name: 4 hydroxy 3 coumarinyl 3 phenyl 3, 4 bromo 4 biphenyl, 1 proponal 1 (Fig. 1). Fig. 1. Structure of bromadiolone. Bromadiolone acts as a classical indirect anticoagulant, i.e. it interferes with Vitamin K activity, but its potency is about 10 times greater than that of warfarin in rabbits (Grand loc. cit.). This author also describes laboratory and field tests with bromadiolone against rats carried out in France. The present paper gives details of tests with bromadiolone against laboratory strains of Rattus norvegicus and Mus musculus particularly in feeding tests. Preliminary results from field trials in England against warfarin resistant R. norvegicus are also given. MATERIALS AND METHODS Laboratory Studies T.O. mice and Wistar rats were used for both the oral dosing and feeding studies. Mice weighed approximately 24-26g and rats 150-200g and equal numbers of males and females were used in all tests.