Letter to Editor: Exceptions to Vertebrate Pest Conference Report

The author responds to a description of his owl mortality presentation. He notes that only one of the six owls that had died had any trace of the brodifacoum rodenticide in its tissues and that owl was electrocuted. The rodenticide was not the cause of its death. The author calls for more dialogue between humane organizations and those involved in pest control

Status of PP581 (Volak) Rodenticide Development

In the Proceedings of the first Eastern Pine and Meadow Vole Symposium (March 1977, Winchester VA), ICI was introduced and basic technical information on PP581 presented. PP581 is a second-generation anticoagulant rodenticide, with the approved common chemical name of brodifacoum. The compound is also known as TALON™ in the form of 50 ppm (0.005%) grain-base pelletized bait as developed for control of commensal rodents. The proposed trade name for the orchard formulation of PP581 is VOLAK™. Brodifacoum has been seen to possess several novel characteristics in work with commensal and other rodent species, suggesting a considerable general potential for control of many pest species of rodents and in various use situations. These characteristics are: 1. Single-feeding action for most species. (Defined as giving over 90% control in 1 day no-choice or 3 day choice tests with 50 ppm bait) 2. Effective on anticoagulant resistant rodents. (As based on US and UK lab studies with warfarin-and cross-resistant rats and mice which were successfully killed by PP581) 3. No bait avoidance.(Beyond that avoidance shown by rodents to any new object or foodstuff, bait avoidance is not a factor and bait is well accepted by most rodents. The lapse of several days till death reduces the chance of rodents associating bait ingestion with poisoning symptoms. 4. Antidotable.(Vitamin K1 injections are antidotal, as is the case for existing anticoagulant products) 5. Low hazard. (PP581 baits at 50 ppm should be as safe to most non-target animals and the environment as other antlcoagulants in current use

THE PROBLEM OF ANTICOAGULANT RODENTICIDE RESISTANCE IN THE UNITED STATES

Resistance of commensal rodents to anticoagulant rodenticides is not a new phenomenon. Its confirmed presence in several areas of northern Europe is wel1-documented (Jackson 1969, 1972; Bentley 1969; Lund 1969). Not until 1971 was a similar situation with the Norway rat (Rattus norvegicus) to be demonstrated in the United States (Jackson et al. 1971). Because it represents an initial occurrence, the site and background observations will be described in some detail. The rural area involved around Cleveland School in Johnson County is 25 miles SE of Raleigh, N. C. and about five miles in diameter (fig. 1). The typical farm is small (20-25A) and produces tobacco, corn, and cotton. Animal sheds (some left from days of mule power), small barns, tobacco sheds, and granaries are characteristic. Dirt floors and perforated foundation walls are common. Cleanliness is not a prime requisite, and considerable harborage (farm machinery and parts, lumber piles, tall weeds, junk, old cars) exists. Stored grains are easily accessible, as are dry foods, animal feed, and special supplements (table 1)

Rate of exposure of a sentinel species, invasive American mink (Neovison vison) in Scotland, to anticoagulant rodenticides

Anticoagulant rodenticides (ARs) are highly toxic compounds that are exclusively used for the control of rodent pests. Despite their defined use, they are nonetheless found in a large number of non-target species indicating widespread penetration of wildlife. Attempts to quantify the scale of problem are complicated by non-random sampling of individuals tested for AR contamination. The American mink (Neovison vison) is a wide ranging, non-native, generalist predator that is subject to wide scale control efforts in the UK. Exposure to eight ARs was determined in 99 mink trapped in NE Scotland, most of which were of known age. A high percentage (79%) of the animals had detectable residues of at least one AR, and more than 50% of the positive animals had two or more ARs. The most frequently detected compound was bromadiolone (75% of all animals tested), followed by difenacoum (53% of all mink), coumatetralyl (22%) and brodifacoum (9%). The probability of mink exposure to ARs increased by 4.5% per month of life, and was 1.7 times higher for mink caught in areas with a high, as opposed to a low, density of farms. The number of AR compounds acquired also increased with age and with farm density. No evidence was found for sexual differences in the concentration and number of ARs. The wide niche and dietary overlap of mink with several native carnivore species, and the fact that American mink are culled for conservation throughout Europe, suggest that this species may act as a sentinel species, and the application of these data to other native carnivores is discussed

The Hampshire-Berkshire focus of L120Q anticoagulant resistance in the Norway rat (Rattus norvegicus) and field trials of bromadiolone, difenacoum and brodifacoum

Anticoagulant resistance has been present in Norway rats (Rattus norvegicus) in Hampshire and Berkshire for forty years. All first-generation anticoagulants and two of the second generation, bromadiolone and difenacoum, are resisted by rats carrying the L120Q single nucleotide polymorphism (SNP). A regulatory restriction on the use of resistance-breakers brodifacoum, difethialone and flocoumafen in the UK effectively prevented their use against Norway rats for more than 30 years. During this time, L120Q spread from original localised foci eventually to cover most of central-southern England; with other more dispersed foci elsewhere in the UK. We summarise research on L120Q Norway rats and the field performance of anticoagulant baits against them. Bromadiolone (50 ppm), difenacoum (50 ppm) and brodifacoum (23 ppm) baits were each applied on two farmsteads where it had been established that Norway rats carried the L120Q SNP. Preliminary DNA resistance tests conducted at the farms found only one of 107 rats to be susceptible and 86.9% to be homozygous resistant. The bromadiolone and difenacoum applications were either partially or wholly ineffective; brodifacoum treatments were fully effective. Quantities of active substances used varied between farms and substances; but more bromadiolone and difenacoum baits were applied than brodifacoum baits during the treatments. Results confirm the high incidence of resistance and support advice that bromadiolone and difenacoum should not be used against the L120Q SNP. Prolonged use of resisted anticoagulants has resulted in a high prevalence of homozygosity and resistance spread. Failed treatments result in prolonged feeding on anticoagulant bait and leave Norway rats alive carrying, presumably, high residues. It remains to be seen whether the use of now-permitted effective substances, and the introduction of a rodenticide stewardship regime, will curtail the spread of resistance and reduce anticoagulant residues in wildlife