Anticoagulant Baits Research Articles

Less brodifacoum in baits results in greater accumulation in the liver of captive Rattus norvegicus in a no-choice trail

AbstractAnticoagulants are widely used as potent cumulative rodenticides; however, they are also associated with adverse environmental effects, such as intoxication of non-target animals. To ensure user safety, in the EU the use of anticoagulants containing active substances of > 30 ppm is restricted to professionals as these substances are toxic to reproduction Kat.1 A or B. Therefore, new products with < 30 ppm anticoagulant substance have been developed and registered. While the biological efficacy of these new products has been evaluated, the effect of their application on liver residues in targeted rodents was not examined before product introduction to the market. Our laboratory no-choice study on wild brown rats (Rattus norvegicus) showed that baits with high (50 ppm) and low (25 ppm) brodifacoum concentrations (with identical nontoxic cereal-based food components) presented 100% efficacy, although the 25 ppm bait exhibited significantly higher palatability and 4.5 times higher liver residues. Rats consumed 13.6 and 167.7 g of the 50 and 25 ppm baits, respectively, which corresponded to 3.16 and 14.91 μg/g of brodifacoum liver residues at their time of death. The experiments demonstrated that a decreased concentration of brodifacoum anticoagulant in rodenticide baits may lead to greater accumulation in rodent liver, thus indicating the urgent need to perform a detailed study of the environmental risks of low-concentration anticoagulant baits.

The use of anticoagulants for rodent control in a mixed-use urban environmefent in Singapore: A controlled interrupted time series analysis.

Vector control remains an important strategy in preventing rodent-borne diseases. Studies quantifying the impact of anticoagulant bait use on rodent populations are scarce in tropical settings. This study examined the impact of anticoagulant bait use on three measures of rodent activity in Singapore to inform rodent-borne disease control strategies. Using a controlled interrupted time-series analytical design with negative binomial and linear regression models, the average rodent activity levels were compared in the pre- and post-intervention periods. There was a 62.7% (Incidence Rate Ratio (IRR): 0.373, 95% CI: [0.224, 0.620]) reduction in the number of rodents caught, a 25.8-unit (coefficient = -25.829, 95% CI: [-29.855, -21.804]) reduction in the number of 30 g/unit baits consumed and a 61.9% (IRR: 0.381, 95% CI: [0.218, 0.665]) reduction in the number of marred bait stations relative to the pre-intervention period. There was a rise in all three outcome measures within four months after the post-intervention period. This study provided strong evidence that anticoagulant baits substantially reduces rodent activity. The population resurgence after the post-intervention period reinforces the importance of timing the resumption of control measures aimed at reducing rodent-borne disease transmission.

APPLICATION METHODS OF COUMATETRALYL BAITS TO CONTROL RATTUS RATTUS DIARDII IN HIGH INFESTATION AREAS

The most widely practiced method of rat control in oil palm plantations is by baiting with anticoagulant rat poisons. Two experiments were conducted to study the efficacy and susceptibility of first-generation anticoagulant rat bait, coumatetralyl (0.375%) to control Rattus rattus diardii. In the first experiment, a laboratory trial was conducted to test two commercial coumatetralyl 0.375 per cent rat baits (5 g and 6 g) and one brodifacoum bait (5 g) in comparison with an untreated control. All the three baits provided excellent kill of Rattus rattus diardii. The results indicated that, Rattus rattus diardii from the locality of Sampit in Central Kalimantan was susceptible to first-generation anticoagulant of coumatetralyl and coumatetralyl baits were highly palatable. The laboratory findings prompted to evaluate the efficacy of first-generation bait in the field. The second experiment was conducted in an 18-year-old mature oil palm field to evaluate coumatetralyl rat bait in three baiting treatments to control high rat infestation with high fresh damage (18%; 12%; 15%; 17%) of Rattus rattus diardii. The coumatetralyl wax bait was evaluated with one bait per palm (replacement at 4 days interval), three baits per palm (replacement at 7 days interval) and five baits per palm (replacement at 7 days interval); and an untreated control treatment was included. All the three baiting treatments provided successful control of rats and reduced the rat population to a negligible level. The standard baiting treatment required nine baiting rounds. The three baits per palm and five baits per palm treatments needed eight and five baiting rounds respectively. The fresh damage on fresh fruit bunches (FFB) in all the three treatments were observed to have reduced from high level to 0 per cent. The first-generation coumatetralyl anticoagulant bait was effective for the control of Rattus rattus diardii. Hence, it is good approach to use the first-generation baits (for example coumatetralyl bait) in susceptible rat population areas until such time the change to second generation rodenticide bait is required. Placements of more baits required fewer baiting rounds but may result in over application of baits which lead to high cost. Therefore, multiple bait application is not recommended for routine baiting campaigns. It is relatively an interim measure for quick reduction of rat populations especially in high infestation areas. Keywords: Oil palm, high rat population, baiting, first-generation anticoagulant, coumatetralyl, Rattus rattus diardii.

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.

Effects of brodifacoum and diphacinone exposure on four species of reptiles: tissue residue levels and survivorship.

Anticoagulant rodenticides are used worldwide to control pest rodent species. However, the risks posed to non-target reptiles have not been well characterized. In this study, 46 giant ameivas (Ameiva ameiva), 39 boa constrictors (Boa constrictor), 33 wood turtles (Rhinoclemmys pulcherrima), and 47 green iguanas (Iguana iguana) were orally dosed with one of two levels of either diphacinone or brodifacoum anticoagulant in propylene glycol solutions. Dosages were derived using daily food intake (DFI) equations, converting DFI to an equivalent anticoagulant bait amount and gavaging the solution volume needed to deliver the quantity of anticoagulant in that amount of bait. Animals were dosed on days 0 and 7 and monitored for a further 7 days for signs of anticoagulant intoxication and differences in behaviors and postures. At necropsy on day 14, animals were examined for thoracic and abdominal bleeding, and both tissue and organ samples were taken for histology. Liver and whole-body anticoagulant residues were assessed. No turtles or boas died due to anticoagulant exposure. However, anticoagulant intoxication was suspected in one iguana dosed with brodifacoum. A few treated ameivas died but exhibited no hemorrhaging. Liver residue levels were higher than whole-body remainder residue levels for all species. Unlike the other species, turtles had higher diphacinone residue levels than brodifacoum. Turtles and boas exhibited a relative insensitivity to diphacinone and brodifacoum, while the lizards appeared to be somewhat more sensitive to these compounds. This study provides data for future assessments of the risks to these species associated with anticoagulant use. Published 2019. This article is a U.S. Government work and is in the public domain in the USA.

Screening and prevention of anticoagulant resistance development in house mice: A review

Unrestricted use of anticoagulants has resulted in rodents developing resistance to them. This has caused a series of problems regarding reduction in rodent populations, which has further implicated great economic losses and a serious threat to the health of people and domestic animals. The popular global trend currently is to control rodent populations by applying the least possible amounts of chemicals, which on the other hand implies that several coactive alternative measures need to be applied in an effort to reduce rodent numbers to an acceptable economic level. On the other hand, knowledge of the genetic structure of rodent populations has become an important set of information desirable to have before setting off to apply rodenticides in practice, so as to prevent ineffective use of rodenticides and prevent further spreading of resistant rodent populations. The latest trend of using combinations of low-dose anticoagulant baits requires further research as their effects on susceptible populations are known but their impact on resistant animals is still not clear.

Effectiveness of Snap and A24-Automated Traps and Broadcast Anticoagulant Bait in Suppressing Commensal Rodents in Hawaii

Effectiveness of Snap and A24-Automated Traps and Broadcast Anticoagulant Bait in Suppressing Commensal Rodents in Hawaii

Effectiveness of Snap-trapping, Goodnature A24 Automated Traps, and Hand-broadcast of Diphacinone Anticoagulant Baits to Suppress Invasive Rats (Rattus spp.) and Mice (Mus musculus) in Hawaiian Forest

Invasive rodents (rats and mice) commonly occur on islands and often damage natural resources largely by predation of native species. Suppressing invasive rodent populations and their damages is therefore a common practice in many parts of the Hawaiian Islands, and land managers such as the Army Natural Resources Program on Oahu often control rodent populations by using large-scale rat snap-trapping and Goodnature A24 automated rat traps (henceforth A24s). While rat traps can be effective at suppressing rat populations, mouse populations are not generally suppressed and may expand greatly. In an effort to reduce rodent populations to levels below that accomplished with rat traps alone at a 5-ha mesic forest on Oahu (Ohikilolo), we assessed the effectiveness of a one-time (two application) hand-broadcast of anticoagulant (Diphacinone-50) bait pellets applied at 13.8 kg/ha per application while A24s and rat snap-traps were active. We monitored rat and mouse activity during trapping and before, during, and after the bait applications using tracking tunnels, which are baited ink cards placed in tunnels so that foot prints of animal visitors can be identified. We found that rat trapping alone was effective at reducing rat populations but not the mouse population, and that the one-time hand-broadcast of diphacinone bait reduced both rat and mouse activity to 0% tracking for about 1 month. However, rat and mouse populations rebounded 2 months later to 15% rat tracking and 41% mouse tracking, which were roughly pre-treatment levels. Rat suppression using A24s at Ohikilolo appeared much more effective year-round than at a nearby 26 ha site (Kahanahaiki), though mouse suppression was poor at Ohikilolo relative to Kahanahaiki. The hand-broadcast of diphacinone bait at both Ohikilolo and Kahanahaiki was effective but short-lived, so repeated baiting during the seasonal peaks in rodent abundance and increasing the size of the buffer area would more likely protect target natural resources from rats and mice.

Rat Damage Assessment and Evaluation of some Methods of Control for Rattus rattus on Date Palm and Orange Trees in New Reclaimd Land.

Rodent damage assayed in date palm and orange trees in different locations at El- Wady El- Gadid Governorate (El-Kharga, El-Dakhla, Gharb El-Mawhob and El–Farafra) as new reclaimed lands. In addition, two control methods were studied i.e. chemical control (zinc phosphide and diphacinone anticoagulant bait) and mechanical control (Aluminum sheet rolled around the trees, clean around the trees by rake, the weeds around the trees were removed, demolition of rat burrows by axe and muslin covered the date). Results showed the damage percentages were 37.06 % in El- Kharga, 45.63 % in El-Dakhla, 0.57% in Gharb El-Mawhob and 4.75% in El- Farafra for date palm. While the damage percentages in sweet orange were 28.16% in El-Kharga, 44.08% in El-Dakhla, 4.78% in Gharb El-Mawhob and 9.14% in El-Farafra. In case of bitter oranges damage percentage were 18.61, 28.28, 4.12 and 4.15 % in El-Kharga, El-Dakhla, Gharb El-Mawhob and El–Farafra, respectively. The results of chemical control showed that diphacinone bait was more effective than zinc phosphide. Whereas, zinc phosphide gave 72.43%, while diphacinone achived 89.26 % population reduction of rats in date palm. Concerning orange trees, it was 69.30 and 86.79 % population reduction of rats. Regarding the mechanical methods, the damage percent in date palm declined to zero percentage after using aluminum sheets around palm stem, clean around the palm, remove the weeds and demolition of rat burrows in date palm. While, in case of using the muslin cover, percentage the damage not decreased in date palm. The average damage percentage after using the chemical and mechanical control on date palm in El- Dakhla were 1.39, 1.80 and 0.00 % by zinc phosphide, diphacinone and aluminum sheets, respectively. In conclusion, mechanical control of rats on palm was better than the chemical methods to protect the environment from the impact of rodenticides especially in new reclaimed land.

Efficacy of acute and anticoagulant rodenticide baiting in sugarcane fields of Punjab, India

The aim of this study was to recommend locality-specific rodent pest management techniques for sugarcane using acute and anticoagulant rodenticides during the months when maximum damage is inflicted on the crop in Punjab, India. Sugarcane crops were found to be infested with four rodent species namely: Bandicota bengalensis (Gray and Hardwicke); Mus booduga (Gray); Millardia meltada (Gray) and Golunda ellioti (Gray), with B. bengalensis being the most prevalent species (accounting for 69.45–83.36% of the total catch). Surveys in 11 villages of three districts of Punjab (India) revealed 19.12 ± 12.22% rodent damage to the sugarcane crop during the months of December–January. Rodenticide treatments were conducted in farmer's fields in two districts of Punjab from December 2003 to January 2007. The results revealed that, to protect the sugarcane crop from rodent damage during the months of December–January, the rodenticide treatment may be applied either: (1) by double-baiting with 2% zinc phosphide followed by 0.005% bromadiolone after 15d at 1 kg/ha each, or (2) by single-baiting with 0.005% bromadiolone at 2 kg/ha. The impact of rodenticide treatment in canefields was also evident in the adjoining wheat crop fields where the incidence of rodent damage was less (0.97–3.24%) than in the fields surrounding untreated canefields (3.53–6.22%).

Efficacy of Oat and Pellet Anticoagulant Baits Following Treatment with Oat and Pellet Zinc Phosphide Baits: Implications for Secondary Hazard Management

Author(s): Salmon, Terrell P.; Newman, Peter D. | Abstract: This study was undertaken to demonstrate the efficacy of oat and pellet type anticoagulant baits (0.01% diphacinone) when used following an initial treatment of 2% zinc phosphide oat and pellet type baits for controlling California ground squirrels. Both broadcast oat and pellet anticoagulant treatments following zinc phosphide treatments resulted in apparently good control, although the power of our pellet tests was not strong because of failure in the control plots. Anticoagulant bait use, on a per acre basis, was well below the allowed application rate (10 lbs/acre) because it was applied only where active ground squirrel burrows remained after controlling the entire population with zinc phosphide. No non-target species were found affected by the zinc phosphide or anticoagulant treatments. As a baiting strategy, the combination of zinc phosphide combined with the subsequent selective application of anticoagulant baits was successful. This approach will likely lead to significantly fewer squirrel carcasses with anticoagulant residues, since most are killed with zinc phosphide and subsequently do not pose a significant secondary risk to predators, scavengers, or pets. This baiting strategy has the potential to significantly reduce secondary hazards from ground squirrel baiting.

Assessing the effectiveness of bait stations for controlling California ground squirrels ( Spermophilus beecheyi)

Bait stations are frequently used in wildlife management programs; however, social factors of the target population as well as the design and placement of bait stations may limit their effectiveness and in some cases result in individuals consuming excessive amounts of bait. We conducted field trials to evaluate the effectiveness of bait stations for delivering a first-generation anticoagulant (diphacinone – 0.005%) bait to California ground squirrels ( Spermophilus beecheyi), and the potential non-target hazards associated with this technique. Using a non-toxic bait containing Keystone Oil Blue A as a biomarker, we determined that squirrels within 100 m of a bait station consumed bait. Males consumed more bait than females and were more frequently observed at bait stations. During a monitored baiting program, ground squirrels died between 14 and 42 days after bait station placement. Results of our trials suggest that territorial individuals may exclude others from the bait until they succumb to diphacinone. This may result in some squirrels consuming significantly more bait than necessary to obtain a lethal dose, and contribute to potentially higher secondary hazards in the field.

Influence of vitamin K-rich plant foods on anticoagulant baiting efficacy in wild House Mice, wild Norway Rats, and wild Black Rats

Rodents introduced to islands have caused the extinction of many species of animals. Anticoagulant rodenticides are relied on to eradicate rodents from these islands, but if the rodents are eating plant materials that contain high amounts of vitamin K (the antidote to anticoagulants) anticoagulant rodenticides may not be effective. In a laboratory trial, individually caged Norway Rats Rattus norvegicus, Black Rats R. rattus and House Mice Mus musculus were fed fresh plant material high in vitamin K (Collards [0.62 mg vitamin K per 100 g] and Brussels Sprouts [0.19 mg vitamin K per 100 g]) for a period of 7 days. When presented later with anticoagulant rodenticides (0.0025% brodifacoum pellets or 0.005% diphacinone pellets) along with the diet of plant material, 94% of the rodents died. We conclude from this study that the presence of green feed rich in vitamin K does not reduce the effectiveness of anticoagulant rodenticides. However, we add a word of caution on one of the findings of our study. While we think the low efficacy (75%) we found in the case of brodifacoum and Black Rats was probably an artifact of small sample size in that treatment group, the result warrants further investigation.

Ecological Risk Assessment for Use of Agricultural Rodenticides in California

The California Department of Food and Agriculture holds registrations for four grain-based anticoagulant rodenticides used in agricultural areas in California to control the California ground squirrel. These rodenticides contain either chlorophacinone or diphacinone as the active ingredient at 0.005% or 0.01% by weight, and are applied by either broadcast or spot baiting techniques. Using residue data from recent field studies, an ecological risk assessment was performed for non-target species potentially receiving secondary exposure through consumption of squirrel carcasses. The species of concern included five birds (American kestrel, burrowing owl, common raven, golden eagle, red-tailed hawk) and one highly sensitive mammal, the coyote. Risks to nontarget species were estimated using a risk quotient (RQ) approach, with RQ values calculated using species-specific daily exposure estimates and levels of concern derived from subchronic toxicity studies. Exposure estimates for the birds of concern ranged from 0.05-0.21 mg/kg bw/day for chlorophacinone and from 0.04-0.16 mg/kg bw/day for diphacinone. For chlorophacinone uses, RQs for birds ranged from 0.172-0.724. RQ values for diphacinone were 16-18 times lower. Based on the methodology used and using EPA risk criteria, the RQ data indicate de minimus risks for all avian receptors of concern. Exposure estimates for adult and subadult coyotes spanned a range from 0.009-0.028 mg a.i./kg bw/day depending on the use pattern. RQs for mortality and blood coagulation were generally near, or slightly above, a value of 1.0 for all of the use patterns evaluated; however, because of the conservative exposure assumptions and other factors, it is highly unlikely that ecologically significant effects on coyotes does or could occur due to use of CDFA’s anticoagulant baits. Wildlife incidence data and population modeling studies corroborate this. Based on the weight of evidence, it is concluded that use of CDFA’s rodenticides for spot and broadcast baiting will not cause “unreasonable adverse effects” on coyote populations or those of other predators/scavengers that feed on squirrel carcasses.

Rapid assessment for a new invasive species threat: the case of the Gambian giant pouched rat in Florida

The Gambian giant pouched rat (Cricetomys gambianus) is a large rodent that has established a breeding population in the Florida Keys. Should it successfully disperse to mainland Florida, it could continue spreading through much of North America where significant negative ecological and agricultural consequences could result. We rapidly developed the information for implementing an efficient and successful eradication program before dispersal to the mainland occurs. This included development of monitoring and indexing methods and their application to define the animal’s range, the development of baits attractive to Gambian giant pouched rats, efficacy testing of toxicants, and development of bait-delivery devices that exclude native animals. Gambian giant pouched rats appeared confined to the western two-thirds of Grassy Key, but have dispersed across a soil-filled causeway west to Crawl Key. We identified preferred habitat characteristics and potential dispersal pathways. We developed photographic and tracking tile methods for detecting and indexing Gambian giant pouched rats, both of which work well in the face of high densities of non-target species. We identified a commercial anticoagulant bait and we developed a zinc phosphide (an acute toxicant) bait matrix that were well accepted and effective for controlling Gambian giant pouched rats. We also developed a bait station for delivering toxic bait to Gambian giant pouched rats without risk to native species. We consider that the criteria are met for a successful eradication to commence.

Characterizing and Averting Cottontail Rabbit Damage in a Southern California Nursery

Cottontail rabbits are a serious problem in Southern California. Of particular concern is the damage they do to ornamental plant and tree nurseries. Rabbit browsing reduces plant quality, kills containerized plants, and damages irrigation systems. Although anticoagulant baiting for cottontail rabbits is legal in California, growers should also consider multiple integrated tactics for rabbit damage control. This project employed GPS mapping technology to locate the occurrence of rabbit damage and correlate it with irrigation type, container, planting density, canopy width, and canopy height. GPS was also used to monitor the impact of experimental strategies to reduce rabbit damage. Strategies to reduce rabbit damage included the use of protective covers on irrigation tubing, exclusionary fencing, and trapping. Radiotelemetry was used to confirm the location of suspected rabbit harborages within the nursery. GPS results indicate that 1.27 to 1.9-cm (½ to ¾-in)-diameter irrigation line covers were effective in reducing rabbit damage to the irrigation system. Exclusionary fencing using erosion-control silt fencing acted as an excellent temporary barrier to protect individual growing areas and groups of planting beds, but it was found to be impractical for many nursery situations. Rabbit catch rates increased when traps were used in conjunction with drift fences. General tactics recommended to container nurseries based on these study results include: protecting and modifying irrigation systems, use of exclusionary fencing, trapping in conjunction with drift fencing, and modifying known rabbit harborages where possible.

Grower Evaluation of California Ground Squirrel (Spermophilus beecheyi) Control using Anticoagulant Baits

Author(s): Kowalski, Victor J.; Long, Rachel; Sullins, Jim; Garcia, Sergio; Salmon, Terrell P. | Abstract: California ground squirrels continue to present a significant problem for many facets of California agriculture. The use of diphacinone- and chlorophacinone-treated baits remains the most frequent control method for ground squirrels in agricultural settings. Research suggests no difference in efficacy between the two bait types or between broadcast and spot baiting strategies or bait stations. However, these studies were limited in scope and were conducted exclusively on rangeland sites where there is limited availability of alternate food sources. Studies also suggest that a reduced baiting strategy may be as effective as current label recommendations, but this has received only limited attention in field research. We utilized a new approach in conducting field evaluations of anticoagulant baiting efficacy in different agricultural settings and locations throughout the state. We solicited agricultural producers as cooperators to participate in a field-based evaluation to determine if the reduced baiting strategies are effective under specific agricultural operating conditions. Cooperators were trained in a simple research design and monitored to ensure consistent data collection. The training program included a comprehensive manual on squirrel biology, behavior, and control, as well as information on toxicants and legal measures regarding endangered species. An informal survey was sent to cooperators at the end of the project to evaluate their opinions on the efficacy of control methods. We found no difference in efficacy between baiting methods or strategies. Differences in efficacy were found between chlorophacinone and diphacinone and efficacy was lower in nut orchards than in other settings. Despite no difference in efficacy between baiting methods, more cooperators indicated they would use bait stations than other methods in future ground squirrel control operations.

Rat control strategies in organic pig and poultry production with special reference to rodenticide resistance and feeding behaviour

Once rats have invaded farm buildings, efficient rat control usually requires the application of rodenti-cides. Efficacy of control measures may be lost by physiological resistance to anticoagulant rodenticides and by behavioural reactions of the target rat population. On a farm within the area of anticoagulant resistance in north-west Germany, two consecutive rodenticide treatments were carried out against rats, using different anticoagulant bait preparations. Bait consumption was monitored in combination with direct individual video-monitoring of bait uptake behaviour. Almost half of the rats survived the first three-week treatment using coumatetralyl bait. This result was ascribed to the high overall degree of anticoagulant resistance prevailing in the rat population. The second treatment of the same population using difenacoum bait totally failed to reduce population numbers. Dietary preferences, neophobia, social interactions and habitat structure are important behavioural parameters determining bait uptake. They are discussed in relation to the results of the treatment and a conceptual model for the factors determining rodent control efficacy is presented. The combined results of the two monitoring techniques applied demonstrate the significance of resistance and bait uptake behaviour for the efficacy of rat control measures and suggest the need for adapted rat-control strategies to reduce hygienic problems and the risk of non-target poisoning hazards for livestock and wildlife. This can be achieved if the choices of bait base and active ingredient as well as the methods of bait positioning are adapted to the behavioural peculiarities of the rats and the specific structural conditions on each farm.

Assessing the efficacy of registered underground baiting products for mountain beaver (Aplodontia rufa) control

The mountain beaver (Aplodontia rufa) is a fossorial rodent species endemic to the Pacific Northwest and portions of California. This herbivore inflicts millions of dollars of damage annually to forest seedling plantations. Currently, extensive trapping prior to planting is the most reliable method for reducing damage. With increasing restrictions placed on trapping, forest resource managers need alternative tools to minimize forest damage. This study assessed the potential of four toxicants registered for underground use to control mountain beaver; zinc phosphide, diphacinone, chlorophacinone, and strychnine. Zinc phosphide and strychnine are acute toxicants, whereas diphacinone and chlorophacinone are anticoagulants. Anticoagulants prevent the recycling of vitamin K in the body, which inhibits the production of clotting factors. Efficacy varied among treatments. Zinc phosphide and strychnine were avoided by mountain beaver. Pre-baiting marginally increased acceptance of strychnine, but did not alter mountain beaver acceptance of zinc phosphide. Diphacinone and chlorophacinone were both readily consumed, but only chlorophacinone was 100% effective after a 14-day baiting regime. Subsequently, we tested the effects of diet on the efficacy of diphacinone by varying the availability of food containing vitamin K, the anticoagulant antidote. Restricting access to potential sources of vitamin K appeared to increase efficacy. We conclude that anticoagulants hold some promise as additional tools for managers to reduce mountain beaver populations with chlorophacinone showing the most promise. However, limitations to anticoagulant baits include the necessity of long-term baiting (greater than 10 days), a possible decrease in toxicity if baits contact moisture, and potential primary hazards.

Assessing the efficacy of registered underground baiting products for mountain beaver ( Aplodontia rufa) control

The mountain beaver ( Aplodontia rufa) is a fossorial rodent species endemic to the Pacific Northwest and portions of California. This herbivore inflicts millions of dollars of damage annually to forest seedling plantations. Currently, extensive trapping prior to planting is the most reliable method for reducing damage. With increasing restrictions placed on trapping, forest resource managers need alternative tools to minimize forest damage. This study assessed the potential of four toxicants registered for underground use to control mountain beaver; zinc phosphide, diphacinone, chlorophacinone, and strychnine. Zinc phosphide and strychnine are acute toxicants, whereas diphacinone and chlorophacinone are anticoagulants. Anticoagulants prevent the recycling of vitamin K in the body, which inhibits the production of clotting factors. Efficacy varied among treatments. Zinc phosphide and strychnine were avoided by mountain beaver. Pre-baiting marginally increased acceptance of strychnine, but did not alter mountain beaver acceptance of zinc phosphide. Diphacinone and chlorophacinone were both readily consumed, but only chlorophacinone was 100% effective after a 14-day baiting regime. Subsequently, we tested the effects of diet on the efficacy of diphacinone by varying the availability of food containing vitamin K, the anticoagulant antidote. Restricting access to potential sources of vitamin K appeared to increase efficacy. We conclude that anticoagulants hold some promise as additional tools for managers to reduce mountain beaver populations with chlorophacinone showing the most promise. However, limitations to anticoagulant baits include the necessity of long-term baiting (greater than 10 days), a possible decrease in toxicity if baits contact moisture, and potential primary hazards.