Food-Base Flavor Additive Improves Bait Acceptance by Ricefield Rats

Philippine ricefield rats (Rattus rattus mindanensis) that were accustomed to eating rice grain showed greatly increased preference for granulated rice when it was enriched by the volatiles from ground unpolished rice. This was the best of 11 formulations involving 8 rice components that were tested with an automated brief-exposure preference tester. This formulation was also highly preferred (P < 0.005) over untreated granulated rice in an overnight paired preference test. In a similar test, rice volatiles significantly (P = 0.04) improved the acceptance of a marginally palatable bait. In a test with groups of rats in 3- × 3-m enclosures, the rice volatiles formulation was preferred (P < 0.05) over whole-grain rice, untreated granulated rice, and granulated rice with soybean oil. Finally, cage tests were conducted to determine if the rice volatiles would increase the acceptance of an acute toxicant bait. Rats given a choice between granulated rice with and without 0.2 percent zinc phosphide ate more of the untreated material and showed 50 percent mortality; rats given a choice between untreated granulated rice and the rice volatiles formulation with zinc phosphide ate more (> 2×) of the treated bait and showed 88 percent mortality. These results indicate that intensifying the flavor cues associated with a familiar or preferred food is a fruitful approach in the development of an effective bait enhancer.