No abstract

SUMMARYFeeding tests were carried out in the laboratory to evaluate VVBA 8119 as a potential new rodenticide against wild common rats (Rattws norvegicus), ship rats (R. rattus) and house mice (Mus musculus). The results obtained are compared with data previously obtained for difenacoum, another member of the same series of 4-hydroxycoumarin anticoagulants.With warfarin-resistant and non-resistant common rats, complete kills were obtained using a concentration of 0.0005% for 2 days, or 0 001 % for 1 day: a 1-day test at 0.0005% killed 6 out of 10 and 17 out of 20 of the two types respectively. At 0.005% complete kills of resistant ship rats were obtained after 2 days exposure and of resistant house mice after 1 day, but at 0.002% for 2 days there was some survival. Non-resistant ship rats and house mice were all killed after 2 days feeding on 0.002% bait. In 2-day palatability tests, R. norvegicus showed no significant aversion to the poison at 0.002% and 100% mortality was obtained. The poison was significantly unpalatable to R. rattus at 0.005% and to M. musculus at 0.005% and 0*002 %, although with the last species these concentrations gave complete kills.It is concluded that WBA 8119 has greater activity than other know-n anticoagulants against the three commensal species examined. The laboratory results suggest that concentrations between 0.0005% and 0 002% would be suitable for field use against common rats, and between 0.002% and 0.005% for ship rats and house mice.

No abstract

SummaryThe 2-stage determination is based on changes in blood coagulation activity brought about both by the administration of warfarin in conjunction with vitamin KJ epoxide and by feeding a vitamin K-free diet for 4 days. When it was applied to laboratory-bred rats of known warfarin-resistance genotype, 35/35 homozygous susceptible, 44/44 homozygous resistant and 131/133 heterozygous rats were correctly classified. This method was equally effective in identifying the genotype of wild rats carrying the warfarin-resistance gene, Rw 2 • The procedure is rapid and accurate.

The efficacy of difenacoum as a new anticoagulant rodenticide was evaluated by blood coagulation studies and laboratory feeding tests using warfarin-resistant and non-resistant common rats (Rattus norvegicus), ship rats (R. rattus) and house mice (Mus musculus). Prothrombin assays indicated that the compound had as marked an activity with warfarin-resistant common rats as coumatetralyl had with non-resistant animals. Feeding tests confirmed that 0-005% would be a near-optimal concentration for field use, although there was some evidence of unpalatability. Results with ship rats and house mice were less favourable. Trials with enclosed colonies of warfarin-resistant mice confirmed the laboratory finding that although difenacoum was more effective than all other currently used anticoagulants, it was unlikely to give complete control. It is concluded that difenacoum is a valuable new rodenticide, especiaaly for controlling warfarin-resistant common rats.

Laboratory feeding tests were carried out to determine the efficacy of the anticoagulant rodenticide bromadiolone against Rattus norvegicus, R. rattus and Mus musculus. Using 0.005% bromadiolone, complete kills of R. norvegicus and R. rattus not resistant to warfarin were obtained after exposure to the poison for 1 and 5 days respectively. Warfarin-resistant R. norvegicus were all killed in 4 days, and resistant M. musculus in 12 days. In general, the results resembled those obtained with difenacoum. Acceptance of bromadiolone was very good.

The frequency of monogenic resistance to anticoagulant rodenticides in Rattus norvegicus in an area straddling the England-Wales border was monitored from 1967 until 1975. Rats were trapped on farms and tested in the laboratory by administering a dose of warfarin lethal to susceptibles. The mean incidence of resistance was 44 % and did not change significantly, despite the extensive use of anticoagulants by farmers during the 9-year period. In 1975 more refined techniques showed that the frequencies of susceptible (SS) and resistant (RR) homozygotes were significantly below the Hardy-Weinberg expectations and simple estimates of the relative fitness ratios for the RR, RS and SS phenotypes were 0-37, 1-0 and 0-68 respectively. In two relatively isolated valleys, where selection with anticoagulants was minimal, the frequency of resistance decreased significantly from 57 % to 39 % during 1973-5. The results are consistent with the hypothesis that a balanced polymorphism is being maintained. Selection against susceptible homozygotes by the use of anticoagulant rodenticides, and against the resistant homozygote due to its high susceptibility to a primary deficiency of vitamin K gives the heterozygotes a selective advantage. A number of ecological factors that influence the incidence of the resistance are discussed briefly.

S U M M A R YAggressive behaviour was observed to be rare in small family groups of confined wild house mice, Mus musculus L. Unrelated mice were attacked