Influence of Bait Type and Active Ingredient on Rodenticide Palatability and Efficacy

Abstract:
In a semi natural test system for efficacy evaluation of rodenticidal products according to the Infectious Diseases Protection Act of the Federal Republic of Germany, 80 choice tests with Mus musculus and 62 choice tests with Rattus norvegicus from 1984 to 2010 were evaluated. The tests were conducted with groups of wild strain M. musculus (15 – 27 mice per group), R. norvegicus and R. rattus (5–10 rats per group). Bromadiolone, warfarin and zinc phosphide caused a relatively low mortality in M. musculus (65% to 85%), although the palatability of baits with theses active ingredients was good with >25% bait consumption related to overall food consumption. All products with second generation anticoagulants as well as coumatetralyl as active ingredients caused high mortality rates in choice trials with M. musculus (92% to 98 %). In 72.5% of all choice tests with M. musculus, and in 56% of all choice tests with R. norvegicus a mortality of = 90% was observed. Bait type (bloc, paste or granular bait) had no significant influence on bait attractivity. In experiments with difenacoum (0.005%), a bait uptake of 35% in relation to overall food consumption (bait + challenge diet) was sufficient to achieve a 100% mortality in M. musculus, whereas a bait consumption of 24.5 % resulted in 100% mortality in R. norvegicus. Both values are higher than the recommended 20% given in the Technical Notes for Guidance for Rodenticide Efficacy Evaluation for European biocide product authorisation.