A case of increased tolerance of Raltus tiomanicns (Miller) to brodifacoum and bromadiolone

C. H. Lee, K. A. Kamarudin, Y. P. Tan and C. V. Rajapadman

Abstract

Rattus tiomanicus were live-trapped from some cocoa-coconut fields in Kuala Bernam Estate, Hilir Perak with unsatisfactory bromadiolone or brodifacoum control programmes. The rats were brought back to the laboratory and conditioned for 2 weeks with food and water ad libitum. Six groups (20 males and 20 females in each group) were fed 0.005% bromadiolone in maize-based wax cubes for 1,2,3,4,5 and 6 days no-choice feeding; four groups were fed commercially prepared O.OO3% brodifacoum baits for l, 2, 3 and 4 days, and another group, as control, was fed non-poison wax baits for 6 days. No animal death was observed in the control while mortalities recorded in the bromadiolone tests were 30, 52.5,72.5,87.5,97.5 and 100% and for the brodifacoum tests, they were 57.5,82.5,90 and 100% respectively. Rats that succumbed to the bromadiolone and brodifacoum tests required a higher dose and a longer duration to death compared with that of susceptible rats reported previously. The mean lethal feeding period( LFP₅₀) was 1.74( 1.42-2.02) days for bromadiolone and 0.92 (0'56-1.18) day for brodifacoum. The average mean duration to death of the animals after having consumed a lethal dose was 8.1 days for bromadiolone and 8.4 days for brodifacoum. These findings showed increased tolerance of R. tiomanicus to brodifacoum and bromadiolone. Several of the animals that survived the bromadiolone and brodifacoum feeding tests consumed relatively high doses of the poisons. These rats would survive a pulse baiting programme using brodifacoum or bromadiolone which accounts for unsatisfactory rat control in the field. Total mortality in the 6 -day feeding period on 0.005% bromadi-olone baits or the 4-day feeding period on O.OO3% brodifacoum baits showed that these poisons are still effective against such problem rats.

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