Rodenticide Application Research Articles

Effects of tamper-resistant bait boxes on bait uptake by Norway rats (Rattus norvegicus Berk.)

We compared the quantity of wheat bait consumed by Norway rats (Rattus norvegicus) from: (i) wooden bait trays, made as safe as possible from non-target animals using materials available at trial sites, and (ii) three different, proprietary tamper-resistant rat bait boxes. A balanced Latin square experimental design was used to overcome operational biases that occur when baits of different types are applied simultaneously at the same sites. The consumption of bait from the four different types of bait placement differed significantly and accounted for more than 76% of the total variation. The amount of bait eaten by rats from the bait trays was approximately eight times greater than the quantity eaten from the tamper-resistant bait boxes. The three bait box designs appeared to deter bait consumption by rats to a similar extent. Tamper-resistant bait boxes are essential tools in the application of rodenticides in many circumstances but their use should not be mandatory when it is possible to make baits safe from non-target animals by other means.

Farmers' perspectives of rodent damage and management from the highlands of Tigray, Northern Ethiopian

A farmers' knowledge, attitude and practice (KAP) survey was conducted in the highlands of Tigray, northern Ethiopia, to better understand rodent damage and rodent management from the farmers' perspective. Farmers ( n = 191) from Dogu'a Temben district, were interviewed using a semi-structured questionnaire. The large majority of the farmers stated that rodents are the main pests in crop fields (92.1%) and storage (88.5%). The farmers (64.2%) reported they experienced 100–500 kg ha −1 damage in crop fields, which is equivalent to 8.9–44.7% loss in annual production. There was some overlap between the most common crops grown in the highlands and the most common crops susceptible to rodent attack. Farmers identified barley as the crop most susceptible to rodent attack (76.4%) and the booting stage as the crop developmental stage with the highest rodent abundance and damage. Rodenticide application was the most commonly practiced management strategy in crop fields (51.8%); in storage, farmers mainly keep domestic cats around granaries (80.6%). We recommend a reduction in reliance on chemical rodenticide in crop fields and a shift to a more sustainable rodent management approach to reduce rodent numbers and damage.

Rat Control for the Protection of Endangered Birds, Plants, and Tree Snails on the Island of Oahu, Hawaii

Author(s): Mosher, Stephen M.; Rohrer, Jobriath L.; Costello, Vincent; Burt, Matthew D.; Keir, Matthew; Beachy, Jane; Kawelo, H. Kapua; Mansker, Michelle | Abstract: Since 1997, the Oahu Army Natural Resource Program has been controlling rats using diphacinone rodenticide in small-scale bait station grids in combination with rat traps for the protection of one endangered forest bird species, 5 species of endangered Oahu tree snails, and 9 species of endangered plants in 2 mountain ranges on the island of Oahu. Endangered tree snail and some plant populations are protected year-round. Other plants are only protected during their flowering/fruiting season, with small-scale baiting grids in combination with rat traps; and the Oahu Elepaio is only protected during its breeding season, with small-scale bait station grids in combination with rat traps centered on territories. In May 2009, year-round rat control was initiated over a 26-ha forested management unit on Oahu with 440 snap traps. The New Zealand Department of Conservation current best practice rat kill-trapping technology is being utilized for the first time in Hawaii with this large-scale trapping effort. Rat activity within the management unit will be monitored through the use of tracking tunnels. Forest health (seed rain and seedling germination), endangered plant recruitment, endangered tree snail survival, and native invertebrate abundance will be monitored closely to determine the effectiveness of this large-scale trapping effort. The Oahu Army Natural Resource Program is working towards integrating multiple control methods (bait station grids, large-scale rat trap grids, predator-proof fencing, hand and targeted aerial application of rodenticide) over large-scale areas in an effort to determine the most effective means to control rats in Army-managed areas on Oahu.

Nontarget Risk and Environmental Fate of the Broadcast Application of a Diphacinone Rodenticide at Mōkapu and Lehua Islands, Hawai'i

Invasive commensal rodents such as Rattus spp. and Mus spp. imperil many threatened and endangered native species including plants, invertebrates and birds within Hawai'i and U.S. territories and possessions in the Pacific. In some cases, the eradication or control of invasive rodents could allow natural recovery and active restoration of native species and ecosystems negatively impacted. The broad scale application of rodenticides is a necessary management tool for this purpose, but it is highly controversial to the public and regulatory agencies. There is great perceived and actual risk of nontarget mortality and environmental contamination. One of the conservation uses of rodenticides registered in Hawai'i is the aerial broadcast of rodenticide bait over large areas of native ecosystems on the main Hawai'ian islands, repeated periodically to maintain reduced rodent population levels. Recognizing that the success of this program depends on public and regulatory support, a coalition of state and federal agencies and private landowners have carefully designed Hawai'i’s rodent control program to minimize short- and longterm environmental impacts. In the early 1990s, diphacinone was selected as the primary rodenticide for conservation uses in Hawai'i because of its long track record of safe and effective use in agriculture worldwide. Hawai'i’s program has 5 components: research on efficacy and environmental impacts, regulatory compliance, developing and using local technical expertise, monitoring of rodenticide impacts and native species recovery and public outreach and engagement, particularly at the community level. After many years of generating the efficacy and safety data in support of regulatory approval by the U.S. Environmental Protection Agency (EPA) and the State of Hawai'i, a diphacinone product (Diphacinone–50, Hacco, Inc., Randolph, WI) was approved in 2007 for conservation uses in the U.S. Subsequently, rodenticide pellets containing the active ingredient diphacinone at 0.005% (50 ppm) were broadcast by helicopter in February 2008 on Mōkapu and in January 2009 on Lehua. Mōkapu was the first island in the world where the aerial broadcast of this less hazardous active ingredient was used to eradicate rats. Island eradications in other parts of the world have usually used broad-spectrum active ingredients that are far more persistent and bioaccumulative, thus imparting a much higher risk to nontarget species and the environment. Monitoring of nontarget and environmental effects on Mōkapu and Lehua did not detect diphacinone residues. A number of factors, including state of Hawai'i restrictions on bait entering the ocean, led to rats surviving on Lehua. These projects demonstrate that the aerial broadcast of a rodenticide containing diphacinone can be an effective and safer tool for conservation. Hawai'i is using the results from Mōkapu and Lehua to plan future rat eradication and control projects and continue development of a long-term program.

Eradication of black rats Rattus rattus from Anacapa Island

Removing invasive rats from islands is a powerful conservation tool, and practitioners are now targeting larger islands for rat eradication. As they do so, they face the challenge of mitigating for potential non-target impacts on native biodiversity that may be susceptible to rodenticides. We report on the eradication of black rats Rattus rattus from Anacapa Island, California, in 2001–2002, which was the first-ever invasive rodent eradication from an entire island where an endemic rodent was present and the first aerial application of a rodenticide in North America. As a mitigation strategy we staggered the rodenticide application over 2 years and held a representative sample of the Anacapa deer mouse Peromyscus maniculatus anacapae in captivity. We also mitigated for bird species potentially susceptible to brodifacoum poisoning and monitored aspects of the terrestrial and marine environments. The free-ranging native rodent population severely declined following rodenticide applications but reintroduction and translocation efforts were successful, and the population quickly recovered to pre-eradication levels. Non-target impacts also included mortality of raptors, gulls and passerines, including high mortality of rufous-crowned sparrows Aimophila ruficeps obscura despite planned mitigation. All observed non-target impacts are expected to be ephemeral; however, further monitoring should reveal details on the dynamics of those impacts. Brodifacoum was not detected in the marine environment or in significant amounts in terrestrial soil, plants and arthropods. Seabird benefits from the rat eradication were quickly realized.

Bromadiolone susceptibility in wild and laboratory Mus musculus L.(house mice) in Buenos Aires, Argentina

Rodents are major pests in many agricultural systems, where they can cause significant economic losses and involve a sanitary risk. The application of anticoagulant rodenticides for rodent control has showed a decrease in effectiveness through time because of the development of resistant populations and the development of aversion behaviour. The goal of the present study was to test the susceptibility to bromadiolone and the existence of anticoagulant resistance in Mus musculus L. (house mouse) in Argentina. We conducted a feeding test with wild animals captured in poultry farms and a laboratory strain that were fed with bromadiolone bait. Three animals of the field experimental group survived the 21 days study period, while for laboratory animals mortality was 100%. Control field animals which were fed without anticoagulant showed 100% survival. We found evidence of the presence of anticoagulant resistant M. musculus L. in the study area. Feeding behaviour may have contributed to increasing the time of survival, and may be a mechanism that allows metabolic clearance of the bromadiolone. Under field conditions control with anticoagulants would be less effective because animals have alternative food.

Experimental assessment of rodent control on two poultry farms of central Argentina

SUMMARY We experimentally assessed the effect of controlling vegetation height along farm perimeters on the abundance of rodents in 2 broiler poultry farms in central Argentina. We carried out an experimental design based on the before-after–control-impact method. After vegetation treatments, there was a significant decrease in rodent abundance at the perimeter of the farm with control of vegetation height because of the reduction of the Pampean grassland mouse Akodon azarae. In poultry houses, there was a significant decrease in rodent abundance on nonaffected farms because of the reduction of the commensal house mouse Mus musculus domesticus, possibly because of a major collocation of rodenticide. Our results indicate that both the control of vegetation growth at the perimeters and the appropriate timing of rodenticide applications are effective measures for rodent control on broiler poultry farms when both control measures are applied simultaneously. We achieved effective rodent control through an understanding of the habitat use and population dynamics of the species involved and the characteristics of the area where the control program would be applied.

Ground-based rodent control in a remote Hawaiian rainforest on Maui

Effective control of introduced mammalian predators is essential to the recovery of native bird species in Hawai?i. Between August 1996 and December 2004, introduced rodents were controlled within three home ranges of the Po?ouli Melamprosops phaeosoma, a critically endangered Hawaiian honeycreeper. Rats were controlled using a combination of ground-based rodenticide (0.005% diphacinone) application and snap traps. Beginning in August 2001, we monitored the effectiveness of these rodent control efforts. Relative abundances of Black Rats Rattus rattus and Polynesian Rats R. exulans were measured in each of five snap-trapping grids seven times over a 35-month period. Rat populations decreased inside of the rodent control areas, but control effectiveness differed between rat species. During the first year of monitoring, target control levels for R. rattus were consistently achieved in only one of the rodent control areas. Control techniques were refined in areas failing to meet targets. Subsequently, we achieved target control levels for R. rattus more consistently in all three rodent control areas. However, relative abundances of R. exulans did not differ between rodent control and reference areas, indicating that our rodent control techniques were insufficient to reduce population levels of this species. These findings signify a need for further improvement of rodent control methods in Hawai?i, especially for Polynesian Rats, and demonstrate the critical importance of periodic monitoring of the response of rodent populations to management. In the future, managers may need to design rodent control operations targeting R. rattus and R. exulans independently to achieve best results.

Implementation and Evaluation of an Integrated Program for Rodent Control in a Shantytown of Buenos Aires City, Argentina

The objective of this work was to evaluate the efficiency of an integrated program for the control of rodents in a shantytown of Buenos Aires City, Argentina. This program was developed in one year. During the preparation phase, an environmental survey of public spaces and dwellings was conducted in the test area to identify factors favoring the presence of rodents and to determine strategies and management measures to be implemented in the execution phase. Rodent abundance was monitored in the following four periods: (1) during the preparation phase, (2) during the execution phase, (3) immediately after the execution phase, and (4) 90 days after the end of the execution phase. According to the results of the preparation phase, we combined three different strategies to reduce rodent abundance in both dwellings and public spaces of the experimental area: rodenticide application, environmental sanitation in public spaces, and sanitary education. In this area the proportion of dwellings and public spaces with signs of rodent activity decreased significantly from the beginning of the trial to immediately after the end of the execution phase. There was a significant increase in rodent activity 90 days after the execution phase. This work reveals that although rodent infestation can be reduced in urban shantytowns, a long-term policy for sanitation improvement and sanitary education is required to keep rodent populations at safe levels for the community.

Recovery of a rodent community in an agro‐ecosystem after flooding

AbstractThe Dongting Lake region is one of the areas prone to flood disaster in China. Despite the frequent occurrence of flooding in this area, few studies have analysed its effects on rodent communities, especially their recovery after withdrawal of floodwaters. We carried out a study of rodent recovery after flooding of the Dongting Lake region in 1998. Rodent population monitoring in the flooded countryside of the Dongting Lake region was conducted during 1998–2001. The census was conducted in Anzao polder of Anxian County in Hunan Province, where the dike burst in 1998 and thousands of hectares of farmland were flooded from July to October. The results indicate that flood disaster could provide important changes in rodent community structure. Firstly, species abundance in the post‐flood area became less than in the normal area. Striped field mice Apodemus agrarius colonized the flooded area in farmland until March 2000, and Norway rats Rattus norvegicus and house mice Mus musculus occurred in July and December 2000, respectively. The degree of the effect on the rodent community in residential premises is less than that in farmland. However, the rodent community in the flooded area could recover and become similar to the normal community. The recovery of rodent species composition was faster in residential premises than in farmland after flooding. Secondly, there was a similar tendency of the dominant concentration indices between post‐flood and normal areas. Thirdly, inundation for a long period could reduce the species diversity of the rodent community in farmland. The significant difference in abundance was continued to 2000 in post‐flooded farmland; however, the influence on the rodent community in residential premises was less and their diversity indices did not differ in 1999. Similarity indices indicated that variation between post‐flood and normal areas had been gradually becoming low from 1999 to 2001. Finally, the monitoring data showed that rodent populations in the flooded area were less than those in the normal area in the first step after withdrawal of floodwaters. However, the rodent population increased rapidly in the flooded area, and became greater than that in the unflooded area in half a year. The population in the flooded area also increased faster than that in unflooded neighbouring area after the application of rodenticide. Another phenomenon was that the population density of rodents could reach levels greater than the normal area, and may continue for more than 2 years. Flood disasters could reduce population densities and species abundance, species diversity and evenness, while increasing dominant concentration indices of the rodent community. However, after 3 years, the rodent community structure became similar to that in the non‐flooded area, except for high density. The recovery of rodent communities in residential premises was faster than that in farmland for a lesser degree of flooding.

The bioeconomics of controlling an African rodent pest species

The paper treats the economy of controlling an African pest rodent, the multimammate rat, causing major damage in maize production. An ecological population model is presented and used as a basis for the economic analyses carried out at the village level using data from Tanzania. This model incorporates both density-dependent and density-independent (stochastic) factors. Rodents are controlled by applying poison, and the costs are made up of the cost of poison plus the damage to maize production. We analyse how the present-value costs of maize production are affected by various rodent control strategies, by varying the duration and timing of rodenticide application. Our numerical results suggest that it is economically beneficial to control the rodent population. In general, the most cost-effective duration of controlling the rodent population is 3–4 months every year, and especially at the end of the dry season/beginning of rainy season. The paper demonstrates that changing from today's practice of symptomatic treatment when heavy rodent damage is noticed to a practice where the calendar is emphasized, may substantially improve the economic conditions for the maize producing farmers. This main conclusion is highly robust and not much affected by changing prices of maize production.

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.

Factors correlated with the presence of rodents on outdoor pig farms in Denmark and suggestions for management strategies

The correlation between farm characteristics and the occurrence and importance of rodent pests on outdoor pig farms in Denmark was explored in an extensive questionnaire survey. Mice occurred on most farms but were only rarely considered a problem, as opposed to rats, which were controlled on more than half of the farms. A series of trapping studies showed a high small-mammal diversity in and around the pigsties. The presence of rats was positively correlated with farm size, the presence of straw stacks near the pigsties and the use of automatic feeders. Rats were considered a problem more often when open drinking basins were used or when feed was stored near the pigsties. The environment of the farm did not play an important role except to some extent the proximity of hedges. Recommendations for preventative rodent management include avoiding conditions indicated previously, frequent mucking out and movement of huts, keeping feed in rodent-proof containers, avoid spillage of fodder, and general cleanliness. Direct control methods include application of rodenticides with proper consideration for the risk of unintended poisoning of production animals, the use of traps, keeping dogs or cats, and possibly shooting.

Environmental factors associated with rodent infestations in Argentine poultry farms

1. Seasonal variations in rodent infestations were studied at poultry farms in central Argentina as well as the environmental factors associated with rodent infestations at poultry farms. 2. During the summer and winter of 1998 rodent infestation was monitored at 10 poultry farms by means of tracking stations, and 21 environmental variables were selected that a priori could be related with the extent of rodent infestation. 3. There was a higher rodent infestation in winter than in summer. 4. Species detected by rodent sightings at the poultry farms included Akodon azarae, Calomys spp. (C. laucha and possibly C. musculinus) and Mus musculus. 5. In summer, rodent infestation was positively associated with the perimeter of the farm, whereas there was an inverse relationship with the maintenance conditions of the sheds. In winter, rodent infestation was positively associated with the percentage of the borders of the farm covered with vegetation, and with the amount of plant cover, especially the amount of plant cover which was above 20 cm in height. 6. There was no significant relationship between rodent infestation and the time lag since the last application of rodenticide (first-generation anticoagulant) at the farms. 7. These results suggest that strategies for controlling rodents based solely on chemical methods may not be good enough for efficient rodent control. Farms which are properly managed, with a better control of vegetation growth at both the perimeter and within the internal area, in addition to a higher maintenance of sheds have appreciably lower rodent infestations.

Simulation of cotton rat population dynamics and response to rodenticide applications in Florida sugarcane

Alternative deterministic simulation models were compared to test the management consequences of present uncertainty about the degree of density dependence involved in cotton rat population cycles in southern Florida sugarcane fields. Efficacy of rodenticide applied in different months was explored under six different scenarios of density dependence and independence in two population parameters: fecundity and juvenile survival. Output from the six models differed considerably in the number of rats produced, but was remarkably consistent in the most effective months to apply rodenticide. Since models without density-dependent fecundity were inherently unstable and an inverse relationship between fecundity and population size is apparent in field data, such a population-growth mechanism seems possible in Florida sugarcane fields. The model in which fecundity was density-dependent at all times produced rat densities closest to field data. Output from this model was most sensitive to changes in the amount litter size declines as population size increases. Field tests are necessary to validate the general agreement among the models about the most effective months to apply rodenticide.

Non‐toxic control techniques for Microtus spp. in apple orchards1

Alternative control techniques to the use of endrin ground spray were investigated in apple orchards in Washington (US). Non‐toxic control strategies using cultural practices proved highly successful in reducing high populations of Microtus montanus to low levels. Early spring raking and mowing followed by the application of herbicides to a strip along the tree line appeared to have the greatest effect. Regular mowing between the tree rows and the maintenance of bare ground under the trees prevented significant build‐up of the population. Similar cultural work also substantially improved the efficacy of subsequent rodenticide applications. The economic impact of the vole damage on apple orchards, even those composed of mature trees, is substantial and the expense of intensive cultural work is justified where high vole populations are possible.

Potential hazard to eastern screech‐owls and other raptors of brodifacoum bait used for vole control in orchards

AbstractDuring the fall and winter of 1981–82, a study was conducted to evaluate the secondary poisoning hazards associated with a proposed anticoagulant rodenticide, Volid® (10 ppm brodifacoum), when used to control voles (Microtus spp.) in apple orchards. Radio transmitters were attached to 38 eastern screech‐owls (Otus asio), 5 barred owls (Strix varia), 3 red‐tailed hawks (Buteo jamaicensis), 2 great horned owls (Bubo virginianus) and 2 long‐eared owls (Asio otus), and the birds' movements were monitored before, during, and after rodenticide applications. Screech‐owls selected woods over alternate habitats for day‐roosting; 73% of daytime locations were in woods. At night, screech‐owls generally were located in woods, orchard, and field‐pasture proportional to their availability, while they avoided cropland. The home ranges of 32 screech‐owls tracked posttreatment included brodifacoum‐treated areas; the proportion of home range treated and habitat use varied among individuals. Minimum mortality was 58% among screech‐owls for which more than 20% of home range was treated, as compared with 17% among those for which less than 10% of home range was treated. Secondary brodifacoum poisoning was the most probable cause of death in six screech‐owls. Of five other screech‐owls found dead posttreatment, four had been consumed by predators and one died of unknown causes. Of six radio‐equipped screech‐owls collected one to two months posttreatment, four contained detectable brodifacoum residue. The fate of 14 of the 32 screech‐owls tracked posttreatment was unknown at the conclusion of radiotracking efforts (63 d after treatment began) because radio contact was lost or the transmitter was dropped; one of these owls was encountered alive in May. Four barred owls tracked posttreatment showed strong selection for woodland habitat and used orchards limitedly; none was found dead posttreatment. One long‐eared owl found dead (not radio‐equipped) was probably killed by secondary brodifacoum poisoning. The results indicate a hazard to screech‐owls and a potential risk to other raptors, given this use pattern and formulation of brodifacoum bait.

Versuch der tilgung eines naturherdes der tularämie und der leptospirose

An endemic area of tularemia and field fever was submitted to a complex surveillance over a period of more than 10 years. In 1977 an epizootic outbreak of tularemia appeared in all four localities studied. The infection rate in small mammals exceeded 10%. F. tularensis was isolated also from different species of ectoparasites. During 1978 the epizootic stopped in 3 foci, but continued to spread in one. Rodenticides (zinc phosphide) were therefore applied in this focus twice annually for 2 1/2 years. Since 1978, tularemia infections disappeared in small mammals as well as in man. The application of rodenticides did not influence the circulation of Leptospira grippotyphosa in small mammals. Their infection rate ranged between 3 and 6%. The reason for this striking difference is seen in the different pathogenesis and transmission of both infections.