Carbon disulfide effects on pre-baited vs. non-pre-baited rats exposed to low dosage zinc phosphide rodenticide bait

Abstract

Control of rodents with rodenticides is frequently ineffective due to bait-shyness and neophobia. In an initial study, to increase bait acceptance, Wistar-strain laboratory rats were individually tested for attraction to 3 odors (rat urine, preputial gland extract, and carbon disulfide) and for repellence to a fourth odor (coyote urine) in a 2-compartment arena. Three measures of rat preference-amount of bait consumed, elapsed time to feeding, and time in each compartment suggested that carbon disulfide at 10 ppm was an attractant ( p=0.003). The other odors produced inconsistent results. In a second study, rats were offered pre-weighed quantities of USA Environmental Protection Agency (EPA) standard challenge bait containing a low level of 0.20% zinc phosphide (ZP) rodenticide. Two groups of rats ( n=28) were given either 0 or 3 days of pre-baiting prior to ZP bait exposure. Half the animals in each group received deionized water placebo odor and the others received the carbon disulfide odor in the presence of baits. EPA bait with carbon disulfide odor produced elevated consumption ( p=0.0099) with females showing a greater degree of effect ( p=0.046). Pre-baiting produced higher mortality (220%) and higher level ZP dosages (30%) during baiting. Although mortality was 11% higher in rats presented ZP bait with carbon disulfide, dosages were unchanged. Relative to pre-baiting, the attractant had a marginal effect on ZP bait acceptance and produced mortality changes in males only. Further development of controlled release of this attractant for rodenticide baits would be needed before field applications are attempted; implications for using attractants in baits, traps, tracking powders to optimally control both rat genders are discussed.