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BACKGROUND: The mechanisms that regulate multi‐annual population dynamics of rodent pest species of cereal crops is often unknown. Better knowledge of such aspects can aid pest management and in turn improve food security and human health. The patterns and processes of the population dynamics of Rattus argentiventer, in rice fields of Indonesia, and Rattus tanezumi, in rice fields of the Philippines were assessed in this article. RESULTS: The meta‐analysis of trapping data over 20 years in Indonesia, and 16 years in the Philippines indicated that rodent populations in rice fields did not show a regular multi‐annual pattern. Rattus argentiventer populations in Indonesia responded to less rainfall from the current year. Rattus tanezumi populations in the Philippines responded positively to both rainfall and rainfall anomaly with a 1‐year time lag. CONCLUSIONS: Our study of long‐term population data indicates that certain combinations of rainfall parameters could be useful to predict years when there is higher rodent abundance in rice fields. The key rodent pest species in rice fields in Indonesia (R. argentiventer) and the Philippines (R. tanezumi) differ, and the populations of each species respond differently to rainfall anomalies. Other factors such as crop cover and water availability may also be important and should be considered in future work. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Baiting is widely used in wildlife management for various purposes, including lethal control, fertility control, disease and parasite control, and conditioned aversion programs for many invasive vertebrate species. The efficacy of baiting programs relies on the likelihood that target animals will encounter the bait, consume it and receive an appropriate dose of the active ingredient. However, there has been little focus on encounter rate of toxic baits combined with behavioural aversion, which are likely to be significant factors affecting efficacy.Following optimal foraging theory, the likelihood of an animal encountering and consuming a toxic grain bait should increase in proportion to its availability relative to background food quantity if it is neither more or less detectable or palatable. Furthermore, the probability of consuming toxic baits might also be influenced by bait aversion following ingestion of a non‐lethal dose of toxin.Using a model system of wild house mice (Mus musculus L.) in mouse‐proof enclosures in Australia, we manipulated background food, applied zinc phosphide (Zn3P2) baits and measured mouse mortality. When background food was scarce, mouse mortality was high, whereas an increasing abundance of background food led to reduced mortality. A scenario modelling random encounters and including bait aversion explained 78% of the variation in observed mortality outcomes and achieved a closer fit to the data than modelling random encounters alone. Mortality rates were predicted to be higher with a higher strength bait, which would overcome behavioural aversion.Ensuring that animals locate and consume a lethal dose of toxic bait is a critical factor for successful bait delivery and efficacy. This is particularly significant in toxic baiting programs, where sublethal doses can make animals feel sick, leading to a negative association with the bait, and the development of aversion.Synthesis and applications: Our findings explain why some toxic baiting programs might fail. To achieve successful control, efforts should be directed at reducing the availability of background food to increase the probability of encounter and uptake of toxic baits. It is important to measure and understand the role of background food on toxic baiting programs to explain variable outcomes and inform strategies for successful bait delivery. [ABSTRACT FROM AUTHOR]

AbstractRodent pests pose significant impacts to agricultural systems and public health globally. Effective strategies for sustainable management while minimizing environmental impacts are crucial. To address the multifaceted nature of rodent impacts, well-coordinated initiatives are necessary to support control strategies, raise awareness among authorities, and inform the public. There is increasing global evidence of Working Groups delivering successful management of a range of natural resource management issues. We outline three case study working groups to tackle rodent pests: (1) National Mouse Group in Australia to manage mouse plague impacts, (2) Working Group Common Vole Management in Germany to manage common vole impacts, and (3) FREDON network for vole management in France. Each working group evolved independently, but all have remarkably similar structures, including monitoring, modelling/forecasting, regular stakeholder meetings (including producers, researchers, government agency staff and others), developing advice for management and identifying research priorities. The success of these working groups was related to: (1) broad stakeholder engagement (particularly farmers/producers), (2) dedicated funding to conduct direct research to inform control strategies, (3) maintained momentum through all phases of rodent population cycles, and (4) benefit for all stakeholders. As rodenticides are increasingly restricted, such working groups will become more important in the future, because stakeholder engagement is necessary to develop rodent management “toolboxes”. [ABSTRACT FROM AUTHOR]

Radio tracking can be used to collect information about animal movement, home range, behaviour and habitat use. Many field studies have fitted radio transmitters to small rodents using permanent nylon cable tie collars and successfully collected movement and fate data. The approach to animal welfare within the context of scientific research prioritises minimising adverse effects on the research animals. Although a range of electronically activated release mechanisms exist in radio tracking collars for larger mammals, weight and size restrictions make these unsuitable for smaller animals (<30g). Our aim was to identify a radio transmitter model and attachment method of an appropriate size and weight that would remain attached to a house mouse (Mus musculus) for >20 days to collect movement data -- and then detach or show signs of detaching after 30 days. Laboratory and field trials identified that a cable tie collar with a cotton thread weak-link and customised radio transmitter was suitable for wild house mice in cropping paddocks. Glue-on methods did not stay attached for long enough to obtain more than a few days of tracking data. [ABSTRACT FROM AUTHOR]

About 70% of the current energy intake of the human population in southeast Asia is met by rice. Rats, especially the ricefield rat, Rattus argentiventer, cause significant pre- and post-harvest losses in rice-based agro-ecosystems of southeast Asia and therefore require appropriate management. Current management practices focus on culling animals when populations are high and after significant damage has already occurred. The use of legal and illegal poisons poses a considerable threat to non-target species and humans. This is of particular concern in regions where rats are often consumed by humans to provide an important protein supplement to their diet. During the last seven years, CSIRO’s rodent research group has tested and refined several methods aimed at decreasing pre-harvest rodent damage in cooperation with the Indonesian Research Institute for Rice and the Vietnamese National Institute for Plant Protection. These methods include exclusion of rats by fencing and physical control by trap-barrier systems with lure crops. The effects of these technologies were investigated regarding the regulation of rat numbers (physical control), damage (exclusion, physical control) and yield (physical control). The results are promising, indicating yield increase, of up to 20% in some cases. Integration of these methods with improved field sanitation, crop synchronisation and more efficient timing of other physical methods of control should result in pronounced increases in yield and improved cost effectiveness. Our approach is contingent on a strong understanding of the ecology of specific rodent pests. Measures of success besides decrease in rat numbers and damage are an increase in farmers’ net income through yield increase and a decrease in the use of chemicals. Pros and cons of these methods in different economic and cultural environments are discussed.

During 1995 to 1997, the efficacy of early tactical management of mouse populations in a project based on grain-growing farms in Victoria, Australia was examined. Farmers modified their management practices of crops (at sowing, harvest, and land preparation), and managed habitats on the boundary of cropped land (such as fencelines) and around farm buildings. One management practice examined was the effect on mouse populations of controlling weeds along margins of crops. On sites where farmers slashed or sprayed weeds in early spring, there was a comparative reduction in the abundance of mice in late summer compared to untreated sites.

Context: Recent studies have shown that the sensitivity of wild house mice to zinc phosphide (ZnP) in Australia is significantly lower than previously assumed, which may account for the reported variability in efficacy of ZnP baits used for broadacre control of house mice in grain-growing regions. Under laboratory conditions ZnP-coated grains with a new higher dose (50 g ZnP/kg grain) were readily consumed but the efficacy of using grains with this higher dose under natural field conditions has not been tested. Aims: To test whether the newly derived ZnP50 (50 g ZnP/kg grain) was more effective under field conditions than the currently registered ZnP25 (25 g ZnP/kg grain) in reducing populations of house mice during a mouse population irruption. Methods: We used a before–after-control–impact (BACI) design to assess changes in mouse population size under different baiting treatments in a replicated field trial. We assessed changes in mouse abundance in recently sown paddocks with either ZnP50 (n = 3) or ZnP25 (n = 3) compared with unbaited control sites (n = 3). Key results: Baiting with ZnP50 led to a median reduction in mouse numbers of >85%. Our modelling showed that under similar circumstances, using the ZnP50 formulation should deliver >80% reduction in population size most (>90%) of the time. In contrast, the current registered bait (ZnP25) achieved approximately 70% reduction in population size, but with more variable results. We would be confident of getting an 80% reduction in population size only 20% of the time by using the currently registered ZnP25 bait under similar field conditions. Conclusions: Consistent with laboratory studies, this study demonstrated the higher probability of achieving a consistently high kill rate under field conditions with the new ZnP50 bait compared with the currently registered formulation (ZnP25). Implications: By using the new ZnP50 bait, farmers are far more likely to get good kill rates, thereby reducing the need for repeated baiting (which is costly and generally ineffective at protecting newly sown crops). Using the new bait should result in lower control costs for farmers and fewer toxic grains being spread to control mice. Recent studies have shown that the tolerance of wild house mice to zinc phosphide (ZnP) in Australia is significantly higher than previously assumed, which may account for the reported variability in efficacy of ZnP baits used for house mice control in grain-growing regions. We used a BACI design to show that a newly derived ZnP50 bait is more effective under field conditions than the is currently registered ZnP bait in reducing populations of house mice during a mouse outbreak. Photograph by Nikki Van de Weyer. [ABSTRACT FROM AUTHOR]

Irregular plagues of house mice, Mus musculus, incur major economic impacts on agricultural production in Australia. The efficacy of zinc phosphide (ZnP), the only registered broadacre control agent for mice, is reported as increasingly variable. Have mice become less sensitive over time or are they taking a sub‐lethal dose and developing aversion? In this laboratory study, the sensitivity of mice (wild caught; outbred laboratory strain) was assessed using oral gavage of a range of ZnP concentrations. The estimated LD50 values (72–79 mg ZnP/kg body weight) were similar for each mouse group but are significantly higher than previously reported. The willingness of mice to consume ZnP‐coated grains was determined. ZnP‐coated grains (50 g ZnP/kg grain) presented in the absence of alternative food were consumed and 94% of wild mice died. Mice provided with alternative food and ZnP‐coated wheat grains (either 25 or 50 g ZnP/kg grain) consumed toxic and non‐toxic grains, and mortality was lower (33–55%). If a sublethal amount of ZnP‐coated grain was consumed, aversion occurred, mostly when alternative food was present. The sensitivity of wild house mice to ZnP in Australia is significantly lower than previously assumed. Under laboratory conditions, ZnP‐coated grains coated with a new higher dose (50 g ZnP/kg grain) were readily consumed. Consumption of toxic grain occurred when alternative food was available but was decreased. Our unambiguous findings for house mice indicate a re‐assessment of the ZnP loading for baits used for control of many rodents around the world may be warranted. [ABSTRACT FROM AUTHOR]