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Currently, zinc phosphide is the only toxicant registered in bait formulations for controlling prairie dogs (Cynomys spp.). Zinc phosphide-treated oats has been registered as a rodenticide for control of black-tailed prairie dogs (C. ludovicianus) for decades. However, its efficacy and weatherability have been questioned in recent years (Marsh 1987). In contrast, bromethalin is a relatively new acute rodenticide that has been used as an alternative method of control for anticoagulant-resistant commensal rodents (Spaulding and Jackson 1982). Its activity involves the uncoupling of the oxidative phosphorylation process in the central nervous system mitochondria (Van Lier and Ottosen 1981). Both acute and chronic toxicity of bromethalin result in visible signs, such as lethargy and weakness in the hind legs, that have been observed in field studies (Jackson et al 1982). Black-tailed prairie dogs populations have increased recently in Nebraska: aerial coverage of prairie dog towns has increased from 6,000 in 1975 ha to 35,200 ha in 1988 (F. Andelt, pers. commun.). It is possible that the significant limitations on the use of the relatively few prairie dog toxicants available has reduced their use and precipitated a recent increase in prairie dog populations. There is a need for new, environmentally-safe, and cost-effective methods of prairie dog control. We tested the relative efficacy of 2% zinc phosphide-treated oats and 0.008% bromethalin-treated oats for controlling black-tailed prairie dogs.