Laboratory evaluation of WBA 8119 as a rodenticide for use against warfarin-resistant and non-resistant rats and mice.

Feeding tests were carried out in the laboratory to evaluate WBA 8119 as a potential new rodenticide against wild common rats (Rattus 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-resistnat 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 0-0005% 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 known 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.

Laboratory evaluation of difenacoum as a rodenticide.

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.

Field trials of difenacoum against warfarin-resistant infestations of Rattus norvegicus.

The anticoagulant difenacoum was tested at two concentrations, 0-005 and 0-01%, in bait against warfarin-resistant rat infestations in farm buildings. Twelve out of the 14 treatments in which the lower concentration of the anticoagulant was used resulted in complete control. One of the remaining two treatments was probably also completely successful, but in the other a few rats, that were not eating the poisoned baits, were still active after 30 days of baiting. All six treatments done using the stronger concentration of poison were completely effective. Since it took as long to control infestations with 0.01% as with 0.005% difenacoum in treatments carried out under similar conditions, the lower concentration is recommended for use against warfarin-resistant rats.