Reflections on Improvements in the Use of Vertebrate Pesticides in New Zealand: 1996 - 2006 CharlesEason LandcareResearch,Auckland,NewZealand DavidMorgan,PennyFisher, and BrianHopkins LandcareResearch,Lincoln,NewZealand PhilCowan LandcareResearch,PalmerstonNorth,NewZealand ABSTRACT : VertebratepesticidesforwildanimalcontrolinNewZealandcameunderscrutinyinthe1980sand1990s,which engenderedconsiderableresearchtoupdatethetoxicologydatabasesofoldercompounds,suchas1080ordiphacinone,tomeet currentinternationalregistrationstandards.Inparalleltherewasafocusonidentifying“usepatterns”andformulationsthatare effectiveatkillingpestsandlesshazardoustootherwildlife.Improvedbaitqualityandreducedsowingratesfor1080baitfor possum control in New Zealand, down from 10-15 kg of bait per hectare to 1-3 kg, has been accompanied by increased effectivenessandreducednon-targetrisk.Thishasbeencoupledwithanimprovedunderstandingof1080toxicologyandrisk communicationamongstpestcontrolprofessionalsandwiththecommunity.Inaddition, invivo metabolismandpersistencestudies coupledwithfieldsurveyshaveimprovedunderstandingofthetoxicokineticsandnon-targeteffectsofdifferentanticoagulants. This enabled improved choice of tools for island versus mainland use in New Zealand. The risks associated with “one-off” applications of baits containing second-generation anticoagulants for rodent eradication on islands are considered to be very substantially outweighed by the potential benefits to their ecosystems. On the mainland, contamination of wildlife and game species and risk of secondary poisoning have been substantially reduced by switching from second- to first-generation anticoagulants.Finally,thesedevelopmentswerecoupledwiththeidentificationofimprovedbaitsforgroundcontrolofpossums androdents,suchasencapsulatedcyanideandgelbaitscontainingcholecalciferol,whichinturnreducedanover-relianceon1080 and anticoagulants alone. Nevertheless, safer use patterns, improved formulations and target specificity, and new vertebrate pesticidesarestillrequired,andthiswillbeamajorchallengeforthe21 st Century. KEY WORDS : 1080,anticoagulants,NewZealand,non-targets,regulatorytoxicology,toxicokinetics,vertebratepesticides Proc.22 nd Vertebr.PestConf. (R.M.TimmandJ.M.O’Brien,Eds.) PublishedatUniv.ofCalif.,Davis. 2006. Pp.406-412. INTRODUCTION haveremainedlargelyunchanged(Eason etal .2000),the Thechemicalsusedforcontrollingvertebratepestsare waytheyareusedhasimprovedconsiderably. classified as 1) anticoagulants, which include warfarin, Inthe1990s,concernswerefrequentlyexpressedby pindone, diphacinone, coumatetralyl, difenacoum, thecommunitywithregardstotheuseof1080andother bromadiolone, brodifacoum, flocoumafen, and toxins, and there were different concerns amongst pest difethalione,or2)non-anticoagulants,whichincludeany controloperatorsaboutthecontinuedavailabilityoftools substancethatdoesnotfallintheformercategory,such for conservation and Tb control (Seawright and Eason as strychnine, cyanide, zinc phosphide, sodium mono- 1994). It is timely to reflect on the improved use of fluoroacetate(1080),cholecalciferol,andcalciferol. vertebrate pesticides and improvement in community Vertebrate pest control in New Zealand principally support for endangered species protection and disease targets rodents, possums, mustelids, and rabbits and is controlinNewZealand. undertakenusingbaits,usuallycerealpelletscontaininga poison.Thepoisonsmostwidelyusedinclude1080,and Achievement1:QualityAssurancetoEnableReduced anticoagulants and cyanide, with increasing use of AerialSowingRates cholecalciferol.Itislikelywewillneedthesetoolsfor Aerialcontrolusing1080(sodiummonofluoroacetate) the foreseeable future for control of disease and baitshasbeenwidelyusedinNewZealandsincethelate conservationpurposes. 1960s for the control of introduced brushtail possums The risk to non-target wildlife, livestock, pets, or (Trichosurusvulpecula ).Asrecentlyastheearly1990s, humans from baits containing vertebrate pesticides will high application rates of up to 15 kg/ha of 1080 baits be determined in part by the animal’s intrinsic werebeingused.Consideringthatonly1or2baitswere susceptibility,thepropertiesofthepoisonsused(suchas required to kill a possum, these sowing rates were their toxicokinetics), bait design and their deployment excessive.Thiswasprimarilyaconsequenceof1)bait methods, and the site-specific complexities of the food being of highly variable size, toxicity, and palatability, websinareasinwhichtheyareused,whichmaylimitor and 2) baiting coverage being as much as 48% incom- exacerbatetheexposureofnon-targetspecies.Whilstthe plete(Morgan2004).Sincepossumsloseappetite30-60 poisonsusedforvertebratepestcontrolinNewZealand minutes after eating a 1080 bait, it was essential that 406 (a) (b) 20 65 35 55 30 16 55 45 45 25 35 12 20 35 15 8 25 Cost ($/ha) 25 Cost ($/ha) 10 15 4 15 Mean sowing rate (kg/ha) Mean sowing rate (kg/ha) 5 5 0 0 5 1973-77 1978-82 1983-87 1988-92 1993-97 1998-2002 1973-77 1978-82 1983-87 1988-92 1993-97 1998-2002 Years Years Figure1.Meanbaitsowingratesfora)pelletandb)carrotbaitsfrom1973to2002.CPI-adjustedcost(NZ$/ha)forthese controloperationswashighlylinearlyrelatedtoapplicationrate,sothecorrespondingcostforeachapplicationrateis indicatedbytheright-handaxis.Pointsonthegraphsrefertosowingrate (fromMorgan2004) . aerial distribution of small, sublethal baits should be detoxification or breakdown) of 1080 and fluorocitrate avoided, not only to achieve high mortality but also to has been demonstrated in animals and other living avoid the creation of bait-shy surviving populations organisms(Eason etal .1993b). (Morgan et al . 1996) and to reduce the risk to Theearliestreportsonratssuggestedthatsome1080 invertebratesandbirdsthatmayfeedonsmallfragments wasretainedfor1-4days.Inamorerecentstudyusing of bait (Harrison 1978, Notman 1989). Bait specifica- mice, 1080 concentrations in plasma, muscle, and liver tions were therefore developed that converted scientific decreased by half after less than 2 hours. Prolonged understanding of key parameters (e.g., susceptibility to persistenceof1080inanimalsaftersublethalexposureis 1080)intopracticalmanufacturingadvice. unlikely,andthishasbeenconfirmedforlargeranimals, Oncebaitofhigherqualitybecameavailable,itwas suchasrabbits,goats,possums,andsheep(Eason etal . possible to further reduce sowing rates. Field studies 1994). The highest concentrations occur in the blood, were undertaken to assess the coverage achieved in withmoderatelevelsinthemuscleandkidneys,andthe normalaerialbaitingoperations.Largegaps,upto400m lowestconcentrationsintheliver.Alltracesofthetoxin inwidth,wereoftenfoundbetweenbaitingswaths,and arethereforelikelytobeeliminatedwithin1week.The these were potentially refuges in which possums could significance of comparatively rapid metabolism and survive.Sowingbaitsat3kg/hawasaseffectiveasat10 excretionisthat1080isunlikelytobioaccumulateinthe kg/ha, indicating the potential for substantially reducing foodchainandthe“withholdingperiod”forlivestockthat operationalcostsbyusingmachinerycapableofdistribut- aresuspectedofhavinghadcontactwith1080baitscan ing baits uniformly at low rates (Morgan 1994). bedefined(Eason etal .1994). Navigationalguidancesystemswereevaluatedandfound However, for some reason in the 1990s rapid to improve the accuracy of bait distribution such that eliminationof1080wasconfusedwithsafetyandlower complete coverage could be achieved. These findings risk of toxicity. As we all know, 1080 is extremely encouraged the reduction in bait sowing rates that had poisonous, with an LD 50 of 1 mg/kg or less for many beguntooccurasaresultofgrowingexperienceamong species(Atzert1971,Eisler1995). pestmanagers(Figure1),andby1997averagekillshad increasedfrom70%(duringthe1970s)toover90%ata ToxicologyandPathology reducedcostofaroundNZ$9millionannually(Morgan Known affected sites in animals following 1080 et al . 1997) and with reduced non-target mortalities exposure include the heart, lungs, liver, kidneys, and (Spurr2000). foetus.Pathologicalchangescanbeproducedbysingle lethaldosesorprolongedsublethalexposure. Achievement2:ImprovedUnderstandingof1080 In the mid-1990s, a study showed that lesions Toxicology associated with 1080 exposure in sheep included FateinAnimals scattered foci of fibrous tissue in the myocardium and Absorption, metabolism, and excretion studies in mild degeneration in the striatum, hippocampus, and laboratory animals since the 1950s have shown that nucleus tractus solitarius in the brain. However, ewes sublethalamountsof1080areexcretedbothunchanged that survived exposure to 1080 (including single and and as a range of non-toxic metabolites. In laboratory repeateddosesfor5days)didnotexperienceanyadverse rodents dosed with sublethal doses, 1080 is rapidly long-term effects (Wickstrom et al . 1997). Although absorbed and distributed through the soft tissues and 1080 itself is not cumulative, studies in sheep and organs.Thiscontrastswiththeactionofcommonlyused laboratoryratsdemonstratethatcumulativedamagetothe anticoagulant rodenticides, such as brodifacoum, which heartorotherorganscanoccurfromrepeatedexposureto are extremely persistent. Sodium monofluoroacetate is sublethal doses of 1080 (Wickstrom et al. 1997, Eason excreted as unchanged fluoroacetate and a range of and Turck 2002). Obviously, livestock must not be metabolites including fluorocitrate. Defluorination (i.e., allowedaccesstotoxicbaits,andevenpartiallydegraded 407 baits should be regarded as hazardous. Furthermore, does it cause birth defects (i.e.,