repellents to reduce cable gnawing

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Wildlife Damage Management, Internet Center for

USDA National Wildlife Research Center -

Staff Publications

University of Nebraska - Lincoln Year

REPELLENTS TO REDUCE CABLE

GNAWING BY WILD NORWAY RATS

Stephen A. Shumake Ray T. Sterner

Stanley E. Gaddis

National Wildlfe Research Center, Fort Collins, CONational Wildlfe Research Center, Fort Collins, CONational Wildlfe Research Center, Fort Collins, CO

This paper is p osted at DigitalCommons@University of Nebraska - Lincoln.

http://digitalcommons.unl.edu/icwdm usdanwrc/838


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REPELLENTS TO REDUCE CABLE GNAWING BY WILDNORWAY RATSSTEPHEN A. SHUMAKE,' U.S. Department of Agriculture, Animal and Plant Health lnspect~onService, National Wildl~fe

Research Center, Fort Collins, CO 80521, USARAY T. STERNER, U.S. Department of Agriculture, Animal and Plant Health lnspection Service, National Wildlife ResearchCenter, Fort Collins, CO 80521, USASTANLEY E. GADDIS, U.S Departmentof Agriculture, Animal and Plant Health lnspection Service, National W~ldlifeResearchCenter, Fort Coll~ns,CO 80521, USAAbstract: Rodents gnaw communications and power cables, resulting in service interruptions, fires, and othersafety concerns. Commensal rodents such as the Norway rat (Rattus noruegicus)have been implicated in manyof these situations. Two chemical repellents (capsicum oleoresin+apsaicin and denatonium benzoate) at 2.0%mass/mass concentrations in a polybutene carrier (Indopol@-control)were evaluated for repellent efficacy com-pared to a plastic mesh physical barrier material (VexaF) and the polybutene carrier (placebo) alone usinggroups of individually caged wild Norway rats. The materials were applied to short lengths of communicationscable (RG-8U) with the repellents enclosed in electrical shrink tubing around the samples and the plastic meshattached to the samples for 7 days of continuous rat exposure. Measures of damage taken after rat exposureincluded 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, wefound less damage (P < 0.05) using the volume loss measure (cc) for the capsaicin and for the denatoniumgroups than for the polybutane-carrier (placebo) group. Other measures of gnawing damage did not improvestatistical comparisons of the repellents. For all 5 measures of damage, there was a consistent rank orderpattern among the means with capsaicin < denatonium < VexarB < Indopol@-control.

JOURNAL OF WILDLIFE MANAGEMENT 64(4):100*1013Key words: gnawing, rat, Rattus noruegicus, repellent, rodent.

Wild Nonvay rats cause extensive damage toagricultural crops and structures, as well as towire and cable system installations (Cogelia etal. 1976, Colvin et al. 1998). Their primarydamage to communications and power cable in-stallations results from their habit of gnawingon objects to maintain and clear burrows andrunways. As a result, they keep their incisorsground and sharpened.A few reports have been~ublisheddealing with gnawing in wild Norwayrats and pocket gophers (Thomomys talpoides,Geomys bursarius) from the standpoint of cabledamage (Howard 1953, Ramey and McCann1997, Shumake et al. 1999), but the objectivesof most rodent control studies are to definetheir negative economic impacts and to rec-ommend a means for ridding the premises ofall rodents. Certainly, wild rats cannot be tol-erated inside buildings for health and safety rea-sons, and reducing local populations remainsthe main method for dealing with this species.However, the presence of rodents often goesundetected in structures for a considerable time

' E-mail: [email protected]

and repellent chemicals that would protect ca-bling inside of building walls or under crawlspaces would be useful.

Several published reports are also availablethat describe gnawing by gophers and the test-ing of repellent materials to reduce gnawing tounderground cables. Ramey and McCann(1997) reviewed research and development ef-forts to develop cable-gnawing repellents overthe past 3 decades. A few of their cited pub-lished reports describe and define the gnawingdamage incurred by gophers, the chemicals thatproduce repellent effects, and the cable cover-ing materials that ensure physical resistance torodent gnawing. One report (Welch 1954) de-scribed similar problems related to wild Norwayrat gnawing behavior, protection of cables, andprotection of food packaging materials. Recent-ly, Shumake et al (1999) reported the develop-ment of an improved method for deliveringchemical repellents to northern pocket gophersas they attempt to gnaw communications cableby using a plastic shrink tubing material for con-taining the chemicals. We evaluated the efficacyof 2 chemical repellents using plastic shrink

This article is a U.S. government work, and is not subject to copyright in the United States.


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1010 NORWAYRAT REPELLENTS Shumake et al.

tubing with wild Norway rats to deter theirgnawing of communications cables in laboratoryevaluations.MATERIALS AND METHODSAnimalsWild Norway rats (n = 45) were captured inlive traps 2 km north of Loveland, Colorado, in1997. Animals (17 M and 28 F ) were kept un-der quarantine for 2 weeks after capture at theNational Wildlife Research Center (NWRC)Animal Research Building (ARB). They weremaintained individually in wire mesh cages ona diet of Purina Laboratory Rodent Chow (Pur-ina Mills, St. Louis, Missouri, USA) with wateravailable ad libitum throughout quarantine andtesting. Animal colony room temperatures weremaintained at 20-25 " C, but relative humihtylevel was not controlled (generally


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J. Wildl. Manage. 64(4):2000

quantitative cable-damage measures were thentaken for each cable sample: cable mass loss,depth of penetration, width of gnawing, andvolume of material gnawed. We also qualitative-ly assessed cable damage.Analysis

The utility of the 4 quantitative dependentvariables to discriminate repellent effectivenesswas explored using stepwise &scriminant func-tion analyses. Separate discriminant analyses ofthe measures were computed for the stepwiseselection, forward selection, and backward elim-ination options of the STEPDISC Program(SAS Institute 1992). For 1animal in the Vexar@group, width and volume measures were notobtained due to sample loss. Mean group esti-mates were used for these 2 missing values.When 1 measure was found to reliably dis-criminate the gnaw damage amounts among the4 treatments, a 1-way analysis of variance (AN-OVA; Winer 1971) for that measure was usedto compare treatments using a PROC-GLM-ANOVA and Type 3 sums of squares (SAS In-stitute 1992). significant main effects were thenanalyzed using a Student-Newrnan-Keuls pro-cedure (SAS Institute 1992) to compare (a pos-teriori) pairs of treatments at the P < 0.05 level.RESULTSScreen for Cable Gnawing

Of the 45 animals tested for cable gnawing,7 animals severed the samples within 7 days ofexposure. A considerable number of the animals(n = 8) failed to show any gnawing on the RG-8U cable, but the majority of animals (n = 25)showed a Level 3 or higher gnawing intensitythat involved at least penetration of the outercovering without damage to inner cable wires.During screening, 20 animals showed a mod-erate degree of gnawing; for these 20 animals,the measured effects in terms of a f SD wereas follows: cable mass loss of 2.82 C 2.85 g,gnaw depth of 3.00 + 3.03 mm, gnaw width of7.26 + 3.03 mm, gnaw volume of 4.01 f 3.34cc, and a final gnaw rating of 3.00 + 1.45.Repellent Tests

With the chemical repellents added to cablesamples (Fig. I), there were noticeable reduc-tions in the measured mean damage levelswhen gnawing on the Indopol@H-1900 (pla-cebo sample) cable segments was used for acomparison. The 5-point rating scores for the

NORWAYRAT REPELLENTS Shumake et al. 1011

124 CapsaicinDenatonium benzoate

Mass Depth Width VolumeLoss (g) (mm) (cm) (mL)

GNAWING MEASUREFig. 1. Means for quantitative measures of wild Norway ratcable-gnawing damage for 3 repellent treatments versus a pla-cebo control material (Indopola) on samples of commercialRG-8 coaxial cable exposed over 7 days.

placebo, Vexar@, capsaicin, and denatoniumgroups were 3.67 + 0.75, 3.00 + 1.29, 2.30 C1.89, and 2.50 + 1.38, respectively.

Results of the 3 STEPDISC analyses wereessentially identical; analyses of the dependentmeasures showed that volume (cc) of cable lossalone was most discriminative of gnawing dam-age by the rats. Inclusion of this variable intothe function accounted for a maximum 69% ofthe variance.

The volume measure, when used in a univar-iate ANOVA, indicated treatment effects (F3,19= 5.50, P = 0.007). Mean separation tests onthe volume data indicated that both capsaicinand denatonium benzoate treatments producedrelatively lower damage levels (P < 0.05) whencompared to the Indopol@(placebo) treatment.Neither chemical repellent, however, achievedstatistically more damage reduction than Vexar@treatment. For the volume measure, a 5 SD(CC) damage levels were: capsaicin at 1.27 f1.80, denatonium at 1.57 1.46, Vexarm at 4.14+ 3.57, and Indopol@at 6.27 ? 1.75. The orderof damage levels based on means was found tobe consistent for all 5 damage measures withcapsaicin < denatonium < Vexar@< [email protected]

Avery (1997) has previously reported that bymahng the presence of a repellent more de-


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1012 NORWAYRAT REPELLENTSShumake et al . J. Wildl. Manage. 64(4):2000

tectable, discriminable, and memorable one c;inimprove effectiveness through a simple learningprocess such as classical conditioning wherespatially and temporally correlated stimuli arerepeatedly presented. The use of plastic tubingas a matrix for chemical repellents within a po-lybutene (Indopol@)mixture offers a means forensuring a high degree of oral, nasal, and buccalcavity contact by wild Norway rats as they at-tempt to gnaw cable material. The texture ofthis covering could provide the rats with a tex-ture cue closely associated with the imtating ef-fect of capsaicin or the bitter taste of denaton-ium. The latter detections are inferred to bemildly noxious to rats based on feeding expo-sure studies.In a previous study using northern pocket go-phers (Shumake et al. 1999) the repellent effectsof both capsaicin and denatonium on gnawing ap-peared stronger than those exhibited by wild Nor-way rats in the current study. capsaicin, for ex-ample, was shown to produce 95% less gnawingon all quantitative measures (volume, depth,width, and mass) when contained within the tub-ing over cable samples and compared to gnawingon placebo (control) cable samples. In our currentstudy, capsaicin produced a sigdcant and ap-proximate 7540% decrease on the mean volumemeasure compared to the placebo treatment. Theother measures of cable damage for wild rats werelower (45-66%) for capsaicin treatment comparedto correspondmg control samples, but these didnot approach the repellent levels shown by go-phers.Reasons for this apparent species differencein repellent effect are uncertain. They could berelated to behavioral, gross anatomical, or taste-trigeminal chemoreceptor hfferences betweenspecies. Both wild Norway rats and gophers cangnaw through dry material (paper, plastic, fiber)without detectable ingestion when toxic agentsor chemical tracers are added as surface coat-ings (Welch 1954, Ramey and McCann 1997).The volume of cable lost to Norway rat gnawingprovided the most sensitive measure for de-tecting damage reduction and this also providedthe best measure for detecting repellent treat-ment effects in gophers. Volume of cablegnawed would also correlate to a high degreewith functional loss of signals in communica-tions cables (e.g., multi-conductor wire, fiberoptic cables, or radio frequency cables).Other potential sources of repellent chemi-cals such as predator urine or chemically iden-

tified glandular extracts (Clapperton et al. 1989)could be evaluated with the tubing matrix andpolybutene to examine and compare other nat-ural, easily registered agents that could poten-tially discourage gnawing in a wide range of ro-dent species. Swihart et al. (1997) have dem-onstrated, for example, that woodchuck (Mar-mots monax) gnawing damage to trees can bereduced by 85% with topical applications ofbobcat (Lynx mcfus) urine. If this repellent ef-fect is related to an innate avoidance of objectsand areas that have been freshly urine-markedby predators, the material could have applica-tions that could also be combined with an irri-tating capsaicin treatment to further reinforcerodent-gnawing repellence. The predator odorcould, in fact, become a cue for the imtatingeffects of capsaicin treatment.MANAGEMENT IMPLICATIONS

For Norway rats, capsaicin consistently pro-duced the most repellent effects on cable gnaw-ing. This repellent could be contained withinplastic tubing surrounding cables in new instal-lations, or plastic packet materials could be at-tached with adhesives to existing cable locationsthat have a history of rat damage. Costs of thechemicals in the Indopol@base would be a con-sideration because the carrier and high grade,food quality capsaicin cost about $1.05 per mof cable in our study. The shrink tubing cost isanother major consideration when purchased insmall quantities-around $2.62 per m of cable.However, other plastic materials that can beheat sealed are available at a cost of $0.10 perm of cable and further evaluations are under-way with alternate covering materials.ACKNOWLEDGMENTS

We thank K. Hollenbeck for construction ofthe graphics, P. Groninger and R. Engeman forstatistical support, and A. Dale for veterinaryand laboratory animal care during the conductof this study. We also appreciated review com-ments and suggestions for revision of the man-uscript from C. Ramey, B. Petersen, M. Avery,and an anonymous reviewer.LITERATURE CITEDAVERY,M. L. 1997. Repellents: integrating sensorymodalities. Pages 11-17 in J. R. Mason, editor.Repellents in wildlife management: proceedingsof the second Denver Wildlife Research CenterSpecial Symposium. Colorado State University,

Fort Collins, Colorado, USA.


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J. Wildl. Manage. 64(4):2000 NORWAYRAT REPELLENTSShunulke et al . 1013

CLAPPERTON,B. K., E. 0. MINOT,AND D. R. GRUMP.1989. Scent lures from anal sac secretions of theferret Mustela furo L. Journal of Chemical Ecol-ogy 15:291-308.COGELIA,N. J., G. K. LAVOIE,AND J. F. GLAHN.1976. Rodent biting pressure and chewing actionand their effects on wire and cable sheath. Inter-national Wire and Cable Symposium 25:117-124.COLVIN,B. A,, SWIFT,T. B. AND F. E. FOTIIERGILL.1998. Control of Norway rats in sewer and utilitysystems using pulsed baiting methods. Proceed-ings of the Vertebrate Pest Conference 18:247-253.HOWARD,W. E . 1953. Tests of pocket gophers gnaw-ing electrical cables. Journal of Wildlife Manage-ment 17:296-300.RAMEY,C. A., AND G. R. MCCANN.1997. Evaluatingcable resistance to pocket gopher damage-A re-view. Pages 107-113 in C . D. Lee and S. E. Hy-gnstrom, editors. Thirteenth Great Plains WildlifeDamage Control Workshop Proceedings, KansasState University, Agricultural Experiment Stationand Cooperative Extension Service.

SAS INSTITUTE.1992. SASIASSIST software: changesand enhancements. Version 6. SAS Institute,Cary, North Carolina, USA.SHUMAKE,S. A., R. T. STERNER,AND S. E. GADDIS.1999. Repellents to reduce cable gnawing bynorthern pocket gophers. Journal of WildlifeManagement 63:1344-1349.SWIHART,R. K., M. J. MATTINA,AND J. J. PIGNATEL-LO. 1997. Pages 271-284 in J. R. Mason, editor.Repellents in wildlife management: proceedingsof the second Denver Wildlife Research CenterSpecial Symposium. Colorado State University,Fort Collins, Colorado, USA.WELCH,J. F. 1954. Rodent control: a review of chem-ical repellents for rodents. Journal of Agriculturaland Food Chemistry 2:142-149.WINER,B. J. 1971. Statistical principles in experimen-tal design. Second edition. McGraw-Hill, NewYork, New York, USA.

Received 15 November 1999Accepted 24 April 2000.Associate Editor: Clark.

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