Baiting location affects anticoagulant rodenticide exposure of non‐target small mammals on farms

Abstract

BACKGROUND Commensal rodents such as Norway rats (Rattus norvegicus Berk.), black rats (R. rattus L.) and house mice (Mus musculus L.) damage stored produce and infrastructure, cause hygienic problems and transmit zoonotic pathogens to humans. The management of commensal rodents relies mainly on the use of anticoagulant rodenticides (ARs). ARs are persistent and bio‐accumulative, which can cause exposure of non‐target species. We compared the baiting strategies to use brodifacoum (BR) in bait boxes indoors only versus in and around buildings in replicated field trials at livestock farms to assess resulting BR residues in non‐target small mammals. RESULTS When bait was used indoors only, the percentage of trapped non‐target small mammals with BR residues as well as BR concentration in liver tissue was about 50% lower in comparison to bait application in and around buildings. These effects occurred in murid rodents and shrews but not in voles that were generally only mildly exposed. During the baiting period, BR concentration in murids was stable but decreased by about 50% in shrews. CONCLUSION Restricting the application of BR bait to indoors only can reduce exposure of non‐target species. The positive effect of this baiting strategy on non‐target species needs to be balanced with the need for an effective pest rodent management within a reasonable time. More research is needed to clarify which management approaches strike this balance best.

Use of rodenticide bait stations by commensal rodents at the urban–wildland interface: Insights for management to reduce nontarget exposure

“…The pattern of nightly rat activity varied from no activity to an average of 9.6 h of activity at a given station per night. Combining ground and elevated stations, in Session 1 most of the 72 yards with rats had low levels of activity (34 yards), followed by intermediate (25) and high activity (13). In Session 2, 23 yards were characterized as having low activity, 14 yards had intermediate activity, and 10 yards had high activity.…”

“…18 Despite the effectiveness of rodenticides in urban settings, relatively little is known of the behavioral response of commensal rodents to bait applications, presumably because of the challenges of field work in urban areas. 19 Recent studies have tended to focus on agricultural or conservation applications, [20][21][22][23][24][25] which may not be applicable to situations requiring the use of rodenticides in urban areas or at the urban-wildland interface. 26 A better understanding of factors such as bait station neophobia and the effects of placement and rat abundance on bait station use could help pest management professionals effectively control commensal rodents while minimizing exposure of nontarget wildlife.…”

Efficacy of a combined insecticide–rodenticide product on ectoparasite and commensal rodent mortality

“…The anticoagulant compound brodifacoum is toxic for all warm‐blooded organisms, 54, 55 persistent 56 and bio‐accumulative 57 . This can cause risk to nontarget species because of primary exposure if they can access bait 58–60 and secondary exposure via prey items that have consumed an anticoagulant rodenticide (see review 61 ). Fipronil also is persistent and accumulative, 62 may pose risks to nontarget vertebrates (see review 63 ) and invertebrates, 62 and the development of resistance may be an issue 64,65 …”

“…66 Risk mitigation measures (RMMs), particularly professional training and best practice application to limit uptake by nontarget species, have been introduced at the EU and national level for the use of anticoagulant rodenticides in the biocide sector. [67][68][69][70][71] Such measures seem suitable also to minimize the unwanted effects 60 potentially associated with the application of a bait-based combination product with brodifacoum and fipronil. The application of RMMs is important to balance nontarget risks and advantages of the compound (efficacy and palatability) of a combined product that bears potential for the protection of human and animal health by managing rodents, ectoparasites and zoonotic pathogens simultaneously.…”

In Focus: vertebrate management and risk mitigation

“…However, the suitability of measures to achieve the risk mitigation aim has rarely been studied systematically and neither have additional techniques been trialled. A field study presented here indicates that the application of AR bait indoors only can reduce the exposure of non‐target small mammals regarding the percentage of non‐target individuals affected as well as AR liver concentration 15 . Especially in species that tend to use indoor and outdoor habitats such as Norway rats ( Rattus norvegicus Berkenhout) such findings should be considered carefully to avoid compromising rodent management efficacy.…”