Repellents to Reduce Cable Gnawing by Wild Norway Rats

Rodents gnaw communications and power cables, resulting in service interruptions, fires, and other safety concerns. Commensal rodents such as the Norway rat (Rattus norvegicus) have been implicated in many of these situations. Two chemical repellents (capsicum oleoresin-capsaicin and denatonium benzoate) at 2.0% mass/mass concentrations in a polybutene carrier (Indopol®-control) were evaluated for repellent efficacy compared to a plastic mesh physical barrier material (Vexar®) and the polybutene carrier (placebo) alone using groups of individually caged wild Norway rats. The materials were applied to short lengths of communications cable (RG-8U) with the repellents enclosed in electrical shrink tubing around the samples and the plastic mesh attached to the samples for 7 days of continuous rat exposure. Measures of damage taken after rat exposure included mass of cable material damaged, volume loss to gnawing, depth of gnaw penetration, width of gnawing, and a qualitative index of damage based upon visual appearance. Using a stepwise discriminant analysis, we found less damage (P < 0.05) using the volume loss measure (cc) for the capsaicin and for the denatonium groups than for the polybutane-carrier (placebo) group. Other measures of gnawing damage did not improve statistical comparisons of the repellents. For all 5 measures of damage, there was a consistent rank order pattern among the means with capsaicin < denatonium < Vexar® < Indopol®-control.