PREDICTING THE OUTCOME OF RODENTICIDE TRIALS AGAINST NORWAY RATS LIVING ON FARMS

Difenacoum and bromadiolone treatments against Norway rats may fail because: 1) the animals eat little or no bait, 2) reinvasion rapidly offsets any success, or 3) the population contains resistant individuals. By monitoring bait takes and employing independent measures of rat activity such as tracking plates, it is possible to identify, often in the early stages of a treatment, patterns that indicate the contribution of each of these causes to the eventual outcome. If there is no bait take from the majority of bait points visited by rats in the first week then the treatment is unlikely to be successful, no matter how long it continues. Furthermore, treatments carried out on arable farms, where cereals are stored and the environment is relatively undisturbed, are likely to be less successful than those carried out on livestock farms, where alternative food may also be abundant but where the environment is less predictable. Bait takes that persist at the same bait points for longer than 16 days strongly suggest the presence of resistant rats, while immigration may be significantly affecting the treatment if takes recur at more than 30% of points after a period of seven days. Once a given problem has been identified remedial measures can be taken

Control Of Rats Resistant To Second-Generation Anticoagulant Rodenticides

Second-generation anticoagulant rodenticides were introduced to control Norway rats that had become resistant to first-generation compounds. Unfortunately, some rats have become resistant to these as well. The lack of alternative rodenticides with the same attributes of ease of use and relative safety is potentially a serious problem should resistance become so widespread that anticoagulants are no longer effective. However, the second-generation anticoagulants difenacoum and bromadiolone can still be effective provided most rats in a population possess only a low degree of resistance to them. Measures that maximize the uptake of bait, such as using the most palatable formulation, baiting burrows and saturation baiting have to be implemented. The low levels of resistance discovered so far mean that the most potent anticoagulants, such as brodifacoum and flocoumafen, should also control most populations if baits containing either of them are properly applied. These two rodenticides are restricted to indoor use in the United Kingdom and are thus not available to control those rats living outdoors that are highly resistant to all other anticoagulants. Those rats can, however, be controlled with either zinc phosphide or calciferol, preferably after prebaiting. Strategies to manage resistance in the long-term should be implemented before high-degree resistance spreads. One potential tactic is to stop using anticoagulants altogether and allow deleterious pleiotropic effects to reduce the prevalence of resistance in a population. Any attempts to manager resistance are only relevant if the intention is to retain anticoagulant rodenticides, with their undoubted advantages, as the main method of controlling rodent pests

Palatability Of Rodenticide Baits In Relation To Their Effectiveness Against Farm Populations Of The Norway Rat

The palatability of 12 rodenticide baits, formulated to vary from poorly accepted to well accepted, was measured in laboratory choice tests against Wistar and wild-caught Norway rats. The baits, derived from six bait bases and two active ingredients, difenacoum and bromadiolone, were simultaneously tested in the field against 24 farm infestations (2/formulation) in order to investigate the relationship between palatability and efficacy. Bait acceptance in laboratory tests, with EPA meal as the challenge diet, varied from 7.0 to 50.6% for Wistar rats and 3.7 to 85.1 % for wild rats. Changing the challenge diet to a ground-up laboratory animal food significantly increased the apparent palatability of three selected baits to Wistar rats, although the relative pay abilities between the formulations remained the same. Bait acceptance, as measured in the laboratory, was unrelated to the degree of control achieved in farm treatments. The presence or absence of alternative food and whether the baits were placed in containers or applied directly into rat burrows appeared more likely to determine the outcome and overwhelmed any influence due to bait palatability. The combined effect of container- and burrow-baiting reduced the rat populations by an average 96.8% with 16 of the 24 populations tested completely eradicated. The least palatable baits dispensed into burrow entrances controlled rats on all farms, including those with abundant food sources

Control of rats resistant to second-generation anticoagulant rodenticides

Second-generation anticoagulant rodenticides were introduced to control Norway rats that had become resistant to first-generation compounds. Unfortunately, some rats have become resistant to these as well. The lack of alternative rodenticides with the same attributes of ease of use and relative safety is potentially a serious problem should resistance become so widespread that anticoagulants are no longer effective. However, the second-generation anticoagulants difenacoum and bromadiolone can still be effective provided most rats in a population possess only a low degree of resistance to them. Measures that maximize the uptake of bait, such as using the most palatable formulation, baiting burrows and saturation baiting have to be implemented. The low levels of resistance discovered so far mean that the most potent anticoagulants, such as brodifacoum and flocoumafen, should also control most populations if baits containing either of them are properly applied. These two rodenticides are restricted to indoor use in the United Kingdom and are thus not available to control those rats living outdoors that are highly resistant to all other anticoagulants. Those rats can, however, be controlled with either zinc phosphide or calciferol, preferably after prebaiting. Strategies to manage resistance in the long-term should be implemented before high-degree resistance spreads. One potential tactic is to stop using anticoagulants altogether and allow deleterious pleiotropic effects to reduce the prevalence of resistance in a population. Any attempts to manager resistance are only relevant if the intention is to retain anticoagulant rodenticides, with their undoubted advantages, as the main method of controlling rodent pests

Palatability of rodenticide baits in relation to their effectiveness against farm populations of the Norway rat

The palatability of 12 rodenticide baits, formulated to vary from poorly accepted to well accepted, was measured in laboratory choice tests against Wistar and wild-caught Norway rats. The baits, derived from six bait bases and two active ingredients, difenacoum and bromadiolone, were simultaneously tested in the field against 24 farm infestations (2/formulation) in order to investigate the relationship between palatability and efficacy. Bait acceptance in laboratory tests, with EPA meal as the challenge diet, varied from 7.0 to 50.6% for Wistar rats and 3.7 to 85.1% for wild rats. Changing the challenge diet to a ground-up laboratory animal food significantly increased the apparent palatability of three selected baits to Wistar rats, although the relative palatabilities between the formulations remained the same. Bait acceptance, as measured in the laboratory, was unrelated to the degree of control achieved in farm treatments. The presence or absence of alternative food and whether the baits were placed in containers or applied directly into rat burrows appeared more likely to determine the outcome and overwhelmed any influence due to bait palatability. The combined effect of container- and burrow-baiting reduced the rat populations by an average 96.8% with 16 of the 24 populations tested completely eradicated. The least palatable baits dispensed into burrow entrances controlled rats on all farms, including those with abundant food sources

Predicting the outcome of rodenticide trials against Norway rats living on farms

Difenacoum and bromadiolone treatments against Norway rats may fail because: 1) the animals eat little or no bait, 2) reinvasion rapidly offsets any success, or 3) the population contains resistant individuals. By monitoring bait takes and employing independent measures of rat activity such as tracking plates, it is possible to identify, often in the early stages of a treatment, patterns that indicate the contribution of each of these causes to the eventual outcome. If there is no bait take from the majority of bait points visited by rats in the first week then the treatment is unlikely to be successful, no matter how long it continues. Furthermore, treatments carried out on arable farms, where cereals are stored and the environment is relatively undisturbed, are likely to be less successful than those carried out on livestock farms, where alternative food may also be abundant but where the environment is less predictable. Bait takes that persist at the same bait points for longer than 16 days strongly suggest the presence of resistant rats, while immigration may be significantly affecting the treatment if takes recur at more than 30% of points after a period of seven days. Once a given problem has been identified remedial measures can be taken

Control of a Population of Norway Rats Resistant to Anticoagulant Rodenticides

For the first time, it has been unequivocally shown that multiple-feed second-generation anticoagulant rodenticides were ineffective against a population of rats in N.W. Berkshire, UK because of an unusually high prevalence and high degree of resistance. Use of the non-anticoagulant rodenticide calciferol led to a substantial reduction in the population, although primary poisoning of small birds appeared to be greater than with anticoagulant baits. There was strong evidence that many of the surviving rats had developed an aversion towards calciferol-treated bait. A reduction in the degree of anticoagulant resistance in the population was evident after a period of 17 months without anticoagulant use. The long-term strategy to manage the resistant population should integrate non-anticoagulant and anticoagulant rodenticide use to take advantage of possible pleiotropic costs of resistance

HARP-B: a 350-GHz 16-element focal plane array for the James Clerk Maxwell telescope

NRC publication: Ye