Laboratory evaluation of germinated and non-germinated bait base for the management of the house rat, Rattus rattus†

Abstract

Germinated and non-germinated cereals (paddy, Oryza sativa; pearl millet,  Pennisetum typhoides; and ragi, Eleusine coracana) and pulses (green gram,  Phaseolus aureus; black gram, Phaseolus mungo; and Bengal gram, Cicer arietinum) were evaluated to determine their suitability as a bait base for zinc phosphide and bromadiolone for controlling Rattus rattus. Two-choice and multiple-choice experiments were conducted using 10 animals of mixed sex for each experiment to compare bait preference of germinated and non-germinated grains. The results of the two-choice tests revealed that both germinated cereals and pulses were preferred to non-germinated by the test animals. The differences between the quantities consumed were statistically significant (P < 0.01). The results of Duncan’s post hoc multiple comparison tests of germinated grain consumption by R. rattus were categorized into three subsets. The first subset consisted of pearl millet, Bengal gram, ragi and paddy. The second and third subsets consisted of green gram and black gram, respectively. It is concluded that by considering the cost of all four grains (in the first subset) any one of the cheapest among them in the germinated form could be recommended or used as a bait base for any of the two  rodenticides for the management of R. rattus. Based on these results, germinated paddy was chosen (as it is the cheapest among the grains) for the laboratory toxicity studies. The acute toxicity tests (2% zinc phosphide) resulted in 100% mortality of rats under both no-choice and two-choice (germinated paddy with poison versus plain non-germinated paddy bait) tests. A powder formulation of bromadiolone (0.005%)-treated bait yielded 100% mortality of rats in no-choice tests, but only 60% mortality in two-choice tests. These results suggest that the 2% zinc phosphide with germinated paddy as a bait base was preferred over a powder formulation of bromadiolone (0.005%). However, a field efficacy study is required before a final bait formulation recommendation is made.

Key words: bromadiolone, germinated grains, Rattus rattus, zinc phosphide.