Cage Efficacy Trials with Cholecalciferol Plus Diphacinone and Cholecalciferol Plus Brodifacoum Baits Using Richardson’s Ground Squirrels

Abstract

There are many species of ground squirrels in North America and some species can cause substantial damage to agriculture and other resources. Traps and rodenticides are the most commonly used methods to reduce populations and damage. We tested the efficacy of three new formulations of rodenticides containing two active ingredients: cholecalciferol and diphacinone or cholecalciferol and brodifacoum using wild-caught Richardson's ground squirrels. All three formulations had an efficacy of ≥60% and one cholecalciferol and brodifacoum formulation had an efficacy of 90%. Additionally, all formulations had lower concentrations of one or both active ingredients than commercial rodenticides that contain only one of the active ingredients. We also noted that squirrels that died generally consumed much more bait than those that survived. Most of these formulations had high efficacies in previous trials with voles and pocket gophers. We recommend that a field efficacy trial be conducted in a ground squirrel colony.