Census Baiting Research Articles

Bio-efficacy of denatonium benzoate added formulation of bromadiolone against commensal rodents

Present day rodent management technology mostly relies on use of rodenticides, which is unsafe for human beings and other non-targets. Denatonium benzoate (DB) is an intensely bitter and non-toxic substance which is detectable by humans at a concentration of 10 ppb. Denatonium benzoate added wax block formulation of bromadiolone (0.005%) (an anticoagulant rodenticide) was evaluated against commensal rodents (house rat, Rattus rattus and lesser bandicoot rat, Bandicota bengalensis), which are always found in the proximity of pets, domestic animals and human beings. Single day exposure to bromadiolone (0.005%) formulation with DB and without DB in no-choice tests yielded 100% mortality in both the test rodent species in 2–11 days. The amount of poison bait ingested by R. rattus and B. bengalensis for both the formulations did not differ significantly, ranging between 5.87 - 7.30 and 6.51–6.71 g/100 g body weight, respectively. In choice tests in the presence of alternate plain food (broken wheat grain), consumption of both the formulations of bromadiolone (0.005%) (with and without DB) was similar to plain food at both the exposure periods (1 and 2 days), indicating a good acceptability of test rodenticide. However, mortality with a single day exposure to bromadiolone (0.005%) formulation with DB was 70% and without DB was 60–80% in both test rodent species within 3–14 days. With a two days exposure period, mortality was 100% in both the species of test rodents in 3–13 days. Single day choice test between the formulations revealed that intake of baits of both formulations by both the test rodents was similar i.e., in the range of 8.16–8.94 g/100 g b wt (bromadiolone with DB) and 8.20–9.5 g/100 g b wt (bromadiolone without DB) indicating that incorporation of a bittering agent (DB) with bromadiolone did not alter the consumption of poison in both the test species. In field trials the mean control success as assessed by census baiting and trapping methods with the application of bromadiolone (0.005%) with DB ranged between 54.0% (houses and shops) to 68.4% (poultry farms) and was 55.6% (houses and shops) to 68.4% (poultry farms) in treatments with bromadiolone (0.005%) without DB. It can be concluded that denatonium benzoate could be a best additive in rodenticidal formulations as the acceptability, palatability and toxicity in the laboratory and also its performance in field in managing the pest rodents were not altered.

Brodifacoum is effective against Norway rats (Rattus norvegicus) in a tyrosine139cysteine focus of anticoagulant resistance in Westphalia, Germany

The tyrosine to cysteine amino acid substitution at location 139 of the vkorc1 protein (i.e. tyrosine139cysteine or Y139C) is the most widespread anticoagulant resistance mutation in Norway rats (Rattus norvegicus Berk.) in Europe. Field trials were conducted to determine the incidence of the Y139C mutation at two rat-infested farms in Westphalia, Germany, and to estimate the practical efficacy against them of applications, using a pulsed baiting treatment regime, of a proprietary bait (Klerat™) containing 0.005% brodifacoum. DNA analysis for the Y139C mutation showed that resistant rats were prevalent at the two farms, with an incidence of 80.0 and 78.6% respectively. Applications of brodifacoum bait achieved results of 99.2 and 100.0% control at the two farms, when measured by census baiting, although the treatment was somewhat prolonged at one site, possibly owing to the abundance of attractive alternative food. The study showed that 0.005% brodifacoum bait is fully effective against Norway rats possessing the Y139C mutation at the Münsterland focus and is likely to be so elsewhere in Europe where this mutation is found. The pulsed baiting regime reduced to relatively low levels the quantity of bait required to control these two substantial resistant Norway rat infestations. Previous studies had shown much larger quantities of bromadiolone and difenacoum baits used in largely ineffective treatments against Y139C resistant rats in the Münsterland. These results should be considered when making decisions about the use of anticoagulants against resistant Norway rats and their potential environmental impacts.

Incidence of Rodent Pests in Cumin (Cuminum cyminum L.) and their Management

Infestation pattern and extent of damage by rodent pests and their management in cumin crop using secondgeneration anticoagulant rodenticides were studied at farmers' fields in Jodhpur district. Monthly trapping throughout the crop season revealed presence of four species, viz., Tatera indica (45.16%), Meriones hurrianae (29.03%), Gerbillus gleadowi and, an arboreal species, Funambulus pennanti (25.81%). Damage to cumin crop was almost on par at the vegetative growth stage and flowering stage, recording 11.00 and 13.50% reduction in plant stand, respectively. Efficacy of two anticoagulant rodenticides viz., difethiaone (0.0025%) and bromadiolone (0.005%) was evaluated by two census methods simultaneously, viz., live burrow count (LBC) and census baiting (CB). Two treatments of either of the anticoagulants, one at vegetative growth and another at flowering stage, resulted in >80% reduction in pest rodent population. Cost:benefit ratio obtained with bromadiolone (0.005%) baiting was 1:10.8. Thus, poison baiting with anticoagulant rodenticides may be practiced twice at (i) vegetative growth and (ii) flowering stage, for effective rodent management in cumin.

Validating census methods to measure changes in house mouse populations

Tracking and census baiting are two techniques that are commonly advocated for monitoring the size of mouse populations. However, currently these techniques are only able to provide an index of population size, rather than an assessment of absolute numbers. In this study the authors tested the reliability of both tracking (footprints left on tiles of fixed size) and census baiting as indices of population size, and sought to calibrate levels of activity and bait consumption under both semi-natural and field conditions (inside farm buildings). Under semi-natural conditions, census baiting produced more satisfactory population estimates than those derived from tracking activity. An initial field trial established that the optimum bait point density for this technique was 1 point per 2 m. Subsequent field trials demonstrated that the bait census technique offers a way to estimate the approximate size of stable populations of mice (population size = (mean daily bait consumption - 36.3)/2.46). The results to date are sufficiently encouraging to support the use of this cost-effective approach to monitoring mouse numbers in the type of habitats investigated in this study.

Relationship between resistance factors and treatment efficacy when bromadiolone was used against anticoagulant-resistant Norway rats (Rattus norvegicus Berk.) in Wales*

We investigated the relationship between the severity and incidence of resistance among Norway rats (Rattus norvegicus) on a farm in Wales and the subsequent outcome of a practical rodent control operation. Bromadiolone resistance factors were estimated for rats trapped on the farm using the blood clotting response test, and were found to be 2 to 3 for male rats and approximately 6 for females. The incidence of resistance in the rat population was high. Infestation size was estimated by census baiting and tracking, and was found to be substantial, with a maximum of 6.5 kg of bait being eaten on a single night. A proprietary rodenticide (Deadline™), containing 0.005% bromadiolone, was used to control the infestation. The duration of baiting was 35 days and, according to the two methods of assessment used, treatment success was in the region of 87 and 93%. No evidence was observed of a significant impact of resistance on the rat control operation, and the remaining rats of this very heavy infestation would probably have been controlled if baiting had continued for longer.

Sarcocystis singaporensis: Studies on Host Specificity, Pathogenicity, and Potential Use as a Biocontrol Agent of Wild Rats

Host specificity and pathogenicity of Sarcocystis singaporensis were investigated as a prerequisite to a subsequent application of the parasite as a biocontrol agent of wild rats in Egypt. After inoculation of 7 snake species comprising the families Elapidae, Viperidae, Colubridae, and Boidae with sarcocysts, sporocyst development was only observed in a reticulated python. Among amphibians, reptiles, and rodents that orally received various sporocyst doses in the laboratory, 2 x 10(4) sporocysts or more were lethal to roof rats Rattus rattus frugivorous, brown rats Rattus norvegicus, and bandicoot rats Nesokia indica. Sarcocysts developed in Rattus spp. and Nile grass rats Arvicanthis niloticus. Subsequently, the pathogenicity of S. singaporensis was tested under natural control situations offering bait pellets containing high amounts of sporocysts to a free-living population of roof rats, which was monitored by indirect census baiting commonly used in rodenticide evaluation. Ten days after consumption of the bait pellets, the infected population collapsed, leading to a control success of 73%. A negative control population, which received a placebo, remained stable. These data demonstrate for the first time that S. singaporensis can be used as a biocontrol agent of wild rats. However, an immunization experiment with roof rats in the laboratory showed that these are capable of mounting a rapid specific immune response resulting in survival of acute sarcocystosis.

Evaluation of mouse-plague control techniques in irrigated sunflower crops

Three types of poison (parathion, strychnine and bromadiolone) were evaluated with regard to their efficacy in controlling mouse plagues in a standing crop such as irrigated sunflower. Two techniques, mark-recapture and census baiting, were used in these evaluations. Census baiting appeared to give the most realistic appraisal of the efficacy of each poison: by this method the population reductions were estimated as 42, 63 and 90% respectively. Bait was applied into the crop aerially at a rate of 5 kg/ha total coverage. Movement data collected during the mark-recapture study are also discussed in terms of relevance to poisoning strategy.

Trials of the anticoagulant rodenticides bromadiolone and difenacoum against the house mouse (Mus musculus L.).

Laboratory and field trials were conducted to determine the efficacy of the anticoagulant rodenticide bromadiolone against the house mouse (Mus musculus). In laboratory feeding tests, family groups of warfarin-resistant mice maintained in pens and conditioned to feeding on plain foods were offered pinhead oatmeal bait containing bromadiolone at 0.005%. Overall mortality in replicated 21-day poison treatments was 55/58 or 94.8%. Six field trials were carried out, using the same poison bait, against mice infesting farm buildings. Treatment success, estimated from the results of census baitings conducted before and after treatment, ranged between 60.4% and 100%, mean 92.4%. In equivalent field trials using difenacoum, another newly developed anticoagulant rodenticide, the control achieved ranged between 70.2% and 100%, mean 96.0%. Five field trials, three involving bromadiolone and two difenacoum, were not completely successful and the surviving mice were removed for laboratory examination. In 21-day toxicity tests, each animal was fed the poison bait offered to it earlier in the field. Bromadiolone and difenacoum gave kills of 12/21 (57.1%) and 9/11 (81.8%) respectively. The possible emergence of mouse populations resistant to these anticoagulants is considered.

Field trials of brodifacoum (WBA 8119) against the house mouse (Mus musculus L.).

The anticoagulant rodenticide brodifacoum was tested against house mice (Mus musculus L.) infesting farm buildings. In six trials, treatment success was assessed from the results of census baitings conducted before and after treatment. With 0.005% brodifacoum in canary seed/corn oil bait, the control achieved ranged between 92.7% and 100%, mean 98.8%. Two mouse populations were eradicated in 3 to 4 weeks but a few individuals survived each of the other four treatments which lasted 6 weeks. The effectiveness of brodifacoum against mice is compared with that of 0.1% calciferol and 0.025% warfarin in combination. It is concluded that brodifacoum and calciferol warfarin are equally effective in controlling M. musculus but that brodifacoum treatments need to be conducted for a relatively longer period.

Trials of the rodenticide pyriminil against wild house mice (Mus musculus L.).

Pen field trials were conducted to assess the performance of the acute rodenticide pyriminil against the house mouse (Mus musculus L.). Four types of poison treatment were carried out using penned family groups of warfarin-resistant mice supplied with alternative plain foods. In each treatment pyriminil was included at 2% in a wholemeal flour/pinhead oatmeal/corn oil bait. Mortality was highest (46/54; 85.2%) when poison bait was offered for 4 days following 3 days of pre-baiting. The same pre-baiting and poisoning technique was adopted in five field trials carried out against mice infesting farm buildings. The efficacy of each poison treatment was estimated from the results of pre- and post-treatment census baitings; treatment success ranged between 53.7% and 96.7%, mean 80.5%. It is concluded that pyriminil treatments are best carried out after a period of pre-baiting and that when pyriminil is used in this manner it is about as effective as zinc phosphide for the control of mice.

A comparative field trial, conducted without pre-treatment census baiting, of the rodenticides zinc phosphide, thallium sulphate and gophacide against Rattus norvegicus

The effectiveness of the single-dose poison treatments of farm rat infestations, analysed by comparing the weights of the post-treatment census bait takes in covariance with the weights of the prebait takes, showed that treatments with 2-5% zinc phosphide, 0-3% thallium sulphate or 0-3% gophacide were equally effective and significantly better than were treatments with 1% zinc phosphide or 0-1% thallium sulphate. The methodology and sensitivity of different analyses are also considered.

1250. Zirconium in our environment

Present day rodent management technology mostly relies on use of rodenticides, which is unsafe for human beings and other non-targets. Denatonium benzoate (DB) is an intensely bitter and non-toxic substance which is detectable by humans at a concentration of 10 ppb. Denatonium benzoate added wax block formulation of bromadiolone (0.005%) (an anticoagulant rodenticide) was evaluated against commensal rodents (house rat, Rattus rattus and lesser bandicoot rat, Bandicota bengalensis), which are always found in the proximity of pets, domestic animals and human beings. Single day exposure to bromadiolone (0.005%) formulation with DB and without DB in no-choice tests yielded 100% mortality in both the test rodent species in 2–11 days. The amount of poison bait ingested by R. rattus and B. bengalensis for both the formulations did not differ significantly, ranging between 5.87 - 7.30 and 6.51–6.71 g/100 g body weight, respectively. In choice tests in the presence of alternate plain food (broken wheat grain), consumption of both the formulations of bromadiolone (0.005%) (with and without DB) was similar to plain food at both the exposure periods (1 and 2 days), indicating a good acceptability of test rodenticide. However, mortality with a single day exposure to bromadiolone (0.005%) formulation with DB was 70% and without DB was 60–80% in both test rodent species within 3–14 days. With a two days exposure period, mortality was 100% in both the species of test rodents in 3–13 days. Single day choice test between the formulations revealed that intake of baits of both formulations by both the test rodents was similar i.e., in the range of 8.16–8.94 g/100 g b wt (bromadiolone with DB) and 8.20–9.5 g/100 g b wt (bromadiolone without DB) indicating that incorporation of a bittering agent (DB) with bromadiolone did not alter the consumption of poison in both the test species. In field trials the mean control success as assessed by census baiting and trapping methods with the application of bromadiolone (0.005%) with DB ranged between 54.0% (houses and shops) to 68.4% (poultry farms) and was 55.6% (houses and shops) to 68.4% (poultry farms) in treatments with bromadiolone (0.005%) without DB. It can be concluded that denatonium benzoate could be a best additive in rodenticidal formulations as the acceptability, palatability and toxicity in the laboratory and also its performance in field in managing the pest rodents were not altered.

Combined use of rodenticidal dust and poison solution against house-mice (Mus musculus L.) infesting a food store.

1. A food store infested with house-mice (Mus musculus L.) was treated with boxes containing 1% warfarin dust surrounding a solution containing 0·005% sodium warfarin and 5% sugar. The boxes were placed around the bases of the stacks, in the air-lanes between stacks and at eaves height at the gable ends of the store.2. Census baitings with counted numbers of wheat grains showed that the mouse population was reduced by about 95% after 5 weeks of the poison treatment and by almost 100% after 20 weeks.3. The field trial suggests that the combined use of rodenticidal dust and poison solution baiting points is a useful additional method of controlling M. musculus and is most effectively employed against mice living in warm, dry environments.Thanks are expressed to our colleague Mr E. W. Powell, who co-operated in this work.

RAT POPULATIONS AND CONTROL IN TWO ENGLISH VILLAGES

Rat (Rattus norvegicus Berkenhout) populations have been studied in two villages in Devonshire. One village had a human population of 266, the other, of 364. The main activity in each village is mixed farming, with poultry and pig keeping on a small scale.From spring 1947 to spring 1950 visits were made to both villages at six‐monthly intervals. At each visit a relative census of the rat populations was taken. This was done either by test baiting, which records only the visits by rats to bait points; or by census baiting, in which a surplus of wheat is laid each day until the amount taken levels off. The level so reached is a measure of the rat population. Test baiting was found to be less reliable, as an index of changes in the rat populations, than census baiting. In some instances treatments, consisting of one, two or three strikes, i.e. poisonings after prebaiting, were carried out after the census.Complete clearance of a whole village was not achieved on any occasion. Lasting reductions of the rat populations were achieved only by comprehensive double or triple strikes. After such treatments the rat populations took more than a year to recover; probably the recovery to the maximum rat population would often have taken 2 years or more had it been allowed to take place.In each village the rats were distributed in discrete colonies, most of them in farms or chicken runs. Poor hygiene and dilapidation of buildings were important factors in promoting rat infestation. When a new source of food became available near an existing infestation, e.g. as a result of the setting up of a new chicken run, rats soon appeared.Apart from rats five species of small mammals visited the bait points: Mus musculus, Apodemus sylvaticus, Microtus agrestis, Clethrionomys glareolus and Sorex araneus. Their presence was detected by their droppings, by characteristic nibbling of the grain, and by trapping. Allowance was made for their presence in recording the results of census baiting.Mouse activity at the bait points was greatest when the rat population was low, but there is no certain evidence that mouse numbers greatly increased when the rats were reduced.It is suggested that, for effective control and the economical use of manpower, treatments in rural areas should always consist of at least two strikes. It may be expected that such treatments, if carried out with a high degree of thoroughness and efficiency, need normally be carried out only once a year; and it might often be possible to leave an area for 18 months or 2 years.