WARFARIN RESISTANCE IN RATTUS TIOMANICUS (MILLER)

LEE C.H., MUSTAFA MD. D., SOH K.G. AND MOHAN E.

SUMMARY

Rattus tiomanicus from cocoa-coconut fields in Hilir Perak under unsuccessful warfarin control programmes were live-trapped and brought back to the laboratory. They were conditioned and provided with food and water ad libitium. Subsequently two batches (10 males and 10 females each) were provided with 0.25% warfarin in wax maize base for 8 - and 14-days' no-choice feeding while two other batches were given 0.025% bromethalin and scilliroside baits respectively for 1-day. Five out of 20 rats survived the 8-days test while one survived the 14-day feeding period and none survived the bromethalin and scilliroside feeding tests. Animals that succumbed to the warfarin tests required a higher dose and a longer duration to death in contrast to that reported by LEE and MUSTAFA (1982)f or susceptible rats. Intermittent and irregular feeding on warfarin baits were noted in both rats that succumbed and survived the feeding tests. Survived rats consumed baits from half to almost the equivalent to their body weights. Totolerate such high doses, they would definitely survived any warfarin control programmes in the field. This showed that the animals have built up resistance to warfarin. Bromethalin and scilliroside at 0.25% were able to bring about 100% mortality of the rats with low bait consumption and in the case of bromethalin a short duration to death. Bait consumption for bromethalin could be enhanced with delayed death of 1-2 days by having a lower bait concentration. Being able to bring about total mortality, bromethalin with other 'second generation 'rodenticides and/or scilliroside with other acute poisons would be alternatives towards the control of rodents especially in areas with warfarin resistant rats.

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