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Aversive agents are proposed as potential additives to rodenticides to increase selectivity to the target species. Examples of various aversive agent categories are given, including odorants, tastants, and emetics, with examples of evaluations. Tastant additives have been found that do not interfere with rodenticidal efficacy. Denatonium benzoate (commercially available as Bitrex®) is an intensely bitter but non-toxic substance, being increasingly used to adulterate common household materials to reduce the potential risks involved with accidental exposures. No known prior research results have been published concerning the incorporation of Bitrex in rodenticides. Rate determination studies utilizing different rodenticidal formulations were conducted. A Bitrex level of 10 ppm was well accepted by wild commensal rats and mice in laboratory tests of brodifacoum pellet and wax block formulations (TALON®, KLERA T® rodenticides). Bait samples with this level of Bitrex (without anticoagulant) were evaluated in a human taste panel study. Samples with Bitrex were found to show significantly greater average rejection by the panel than similar samples without Bitrex. Field trial results are reviewed, which verified the efficacy of Bitrex-containing commensal rodenticides. The potential role of Bitrex or similar taste deterrents as rodenticide additives is considered opposite accidental toxicant exposure statistics, and perceptions relating to rodenticides and other pesticides.

Anticoagulant resistance was first discovered in UK Norway rats ( Rattus norvegicus Berk.) in 1958 and has been present ever since. The possible detrimental impact of resistance on effective rodent control was quickly recognised, and, for almost three decades, extensive research was conducted on the geographical distribution and severity of anticoagulant resistance in UK rats. Various schemes for the eradication of resistant rats were also implemented. At first, surveys showed resistance only to the first-generation anticoagulants, such as warfarin, chlorophacinone and coumatetralyl, but, later, resistance to the more potent second-generation anticoagulants, such as difenacoum and bromadiolone, was also discovered. Unlike some European countries, where only one or two resistance mutations occur, virtually all known rat resistance mutations occur in the United Kingdom, and five (Leu128Gln, Tyr139Ser, Tyr139Cys, Tyr139Phe and Leu120Gln) are known to have significant impacts on anticoagulant efficacy. Little is currently known of the geographical extent of anticoagulant resistance among Norway rats in the United Kingdom because no comprehensive survey has been conducted recently. At an operational level, anticoagulants generally retain their utility for Norway rat control, but it is impossible to control resistant rats in some areas because of restrictions on the use of the more potent resistance-breaking compounds. This paper reviews the development of resistance in Norway rats in the United Kingdom, outlines the present situation for resistance management and introduces a new resistance management guideline from the UK Rodenticide Resistance Action Group. © 2012 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

BACKGROUND: Anticoagulant resistance in Norway rats at foci in Belgium, Denmark, France, Germany, the Netherlands and the United Kingdom is genetically characterised by the same single nucleotide polymorphism (SNP) and consequent amino acid exchange from tyrosine to cysteine at location 139 of the vkorc1 gene (i.e. tyrosine139cysteine or Y139C). The purpose of this study was to assess the degree of resistance among rats at two infested farm sites in the Y139C focus in Westphalia, Germany, using blood clotting response (BCR) tests, and to determine the practical efficacy of applications of a commercial 50 ppm difenacoum bait (Neokil™) against them. RESULTS: BCR tests showed that the difenacoum resistance factor (RF) among the Y139C rats was about 2.5. DNA analysis for the Y139C mutation revealed that it was present among rats at the two sites with a prevalence of 75 and 93%. Applications of difenacoum bait at the two sites achieved 86.8 and 59.9% control. The different outcomes did not appear to be due to differences either in the degree and prevalence of resistance or in the quantities of poisoned bait consumed. CONCLUSION: The study showed that, although the RF for difenacoum among rats carrying the Y139C SNP was apparently low, an acceptable level of control of resistant Norway rat infestations was not achieved using difenacoum. Continued use of anticoagulants against rats that are resistant to them will exacerbate resistance problems in terms of both increased severity and prevalence. These conclusions are likely to apply elsewhere in Europe where the Y139C SNP occurs. Copyright © 2012 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

BACKGROUND: The aim of this study was to determine the incidence and the level of resistance to bromadiolone among rats on farms suspected of being foci of resistance by using the international normalised ratio (INR)-based blood clotting response (BCR) test. Whether the level of reduced susceptibility constitutes 'practical resistance' was subsequently determined in field trials. RESULTS: The 2.5 multiple of the ED50 baseline was used to test for the incidence of resistance, and higher multiples in the range of the suspected resistance factor were used to investigate the degree of resistance. The ED50 values of bromadiolone in resistant rats were confirmed in the range 4.70-7.05 mg kg−1 for males and 4.62-6.61 mg kg−1 for females. Variations within these ranges appeared between farms. According to the BCR resistance tests, 50-100% of rats were classified as resistant prior to the field trials; 29-100% of rats survived the treatments. CONCLUSION: BCR tests based on the use of the INR and baselines are suitable for determining the incidence and for assessing the level of resistance in populations of Norway rats. The majority of rats of the Westphalian resistant strain, characterised by the Y139C marker in VKOR, are resistant to bromadiolone under practical control conditions. Copyright © 2011 Society of Chemical Industry [ABSTRACT FROM AUTHOR]