Laboratory and field evaluation of three odorant compounds for improving attraction of the lesser bandicoot rat, Bandicota bengalensis (Gray) to 0.0375% coumatetralyl bait

For improving the acceptance of rodenticide bait containing 0.0375% coumatetralyl to control the lesser bandicoot rat, Bandicota bengalensis, a predominant pest in rice and wheat cropping in South Asia, three odorant compounds were tested in bi- and multi-choice laboratory feeding tests and under field conditions. The synthetic form of dimethyl sulphoxide (DMSO), carbon disulphide (CS2) and phenyl acetic acid (PAA), which are considered to be artificial semiochemicals involved in mediating socially induced food choices, were used to amend 0.0375% coumatetralyl baits at the rate of 1.5, 1.0 and 1.0%, respectively. The baits, WSO and RSO, were prepared as mixtures of respectively wheat and rice semolina (particle size 0.000216-0.001 mm3), sugar and groundnut oil in the ratio 93:5:2. DMSO and CS2 improved acceptance of WSO bait by approx. 39% and 65%, respectively, and of RSO bait by approx. 39% and 45% in bi-choice feeding tests. However, PAA-amended WSO bait was avoided by B. bengalensis. These results were confirmed by analysis of behavioural acts relating to attraction and feeding of baits. Plain RSO baits amended with the odorant compounds were preferred to unamended RSO and traditional wheat bait (cracked wheat/sugar/groundnut oil, 96:2:2), but amended 0.0375% coumatetralyl RSO baits were the least preferred in multi-choice feeding tests, so indicating that the rats discriminated against the poison, even in the most preferred bait base, i.e. the plain RSO. The acceptance of both poison baits, WSO and RSO, was not significantly enhanced in wheat fields but significantly enhanced in rice fields by DMSO. PAA significantly increased bait take of RSO poison bait by rodents in both crops, while CS2 non-significantly enhanced take of poison in both bait bases in rice crops, although only in WSO poison bait in a wheat field. In mature rice crops, RSO poison bait treated with DMSO or CS2 was consumed in 2-3 times greater quantities than the alternative wheat bait, thus clearly indicating the usefulness of these odorant chemicals in the control of field rodents.