Developing fertility control for rodents: a framework for researchers and practitioners

Fertility control is often heralded as a humane and effective technique for management of overabundant wildlife,including rodents.The intention is to reduce the use of lethal and inhumane methods,increase farm productivity and food security as well as reduce disease transmission,particularly of zoonoses.We developed a framework to guide researchers and stakeholders planning to assess the effectiveness of a potential contraceptive agent for a particular species.Our guidelines describe the overarching research questions which must be sequentially addressed to ensure adequate data are collected so that a contraceptive can be registered for use in broad-scale rodent management.The framework indicates that studies should be undertaken iteratively and,at times,in parallel,with initial research being conducted on(1)laboratory-based captive assessments of contraceptive effects in individuals;(2)simulation of contraceptive delivery using bait markers and/or surgical sterilization of different proportions of afield-based or enclosure population to determine how population dynamics are affected;(3)development of mathematical models which predict the outcomes of different fertility control scenarios;and(4)implementation of large-scale,replicated trials to validate contraceptive efficacy under various management-scalefield situations.In some circumstances,fertility control may be most effective when integrated with other methods(e.g.some culling).Assessment of non-target effects,direct and indirect,and the environmental fate of the contraceptive must also be determined.Developing fertility control for a species is a resource-intensive commitment but will likely be less costly than the ongoing environmental and economic impacts by rodents and rodenticides in many contexts.

Small mammal community composition impacts bank vole (Clethrionomys glareolus) population dynamics and associated seroprevalence of Puumala orthohantavirus

Rodents are important reservoirs for zoonotic pathogens that cause diseases in humans.Biodiversity is hypoth-esized to be closely related to pathogen prevalence through multiple direct and indirect pathways.For example,the presence of non-host species can reduce contact rates of the main reservoir host and thus reduce the risk of transmission(“dilution effect”).In addition,an overlap in ecological niches between two species could lead to increased interspecific competition,potentially limiting host densities and reducing density-dependent pathogen transmission processes.In this study,we investigated the relative impact of population-level regulation of direct and indirect drivers of the prevalence of Puumala orthohantavirus(PUUV)in bank voles(Clethrionomys glareolus)during years with high abundance.We compiled data on small mammal community composition from four regions in Germany between 2010 and 2013.Structural equation modeling revealed a strong seasonality in PUUV control mechanisms in bank voles.The abundance of shrews tended to have a negative relationship with host abundance,and host abundance positively influenced PUUV seroprevalence,while at the same time increasing the abundance of competing non-hosts like the wood mouse(Apodemus sylvaticus)and the yellow-neckedfield mouse(Apodemusflavicollis)were associated with reduced PUUV seroprevalence in the host.These results indicate that for PUUV in bank voles,dilution is associated with increased interspecific competition.Anthropogenic pressures leading to the decline of Apodemus spp.in a specific habitat could lead to the amplification of mechanisms promoting PUUV transmission within the host populations.

The status of fertility control for rodents—recent achievements and future directions

Management of overabundant rodents at a landscape scale is complex but often required to sustainably reduce rodent abundance below damage thresholds.Current conventional techniques such as poisoning are not species specific,with some approaches becoming increasingly unacceptable to the general public.Fertility control,first proposed for vertebrate pest management over 5 decades ago,has gained public acceptance because it is perceived as a potentially more species-specific and humane approach compared with many lethal methods.An ideal fertility control agent needs to induce infertility across one or more breeding seasons,be easily delivered to an appro-priate proportion of the population,be species specific with minimal side-effects(behavioral or social structure changes),and be environmentally benign and cost effective.To date,effective fertility control of rodents has not been demonstrated at landscape scales and very few products have achieved registration.Reproductive targets for fertility control include disrupting the hormonal feedback associated with the hypothalamic-pituitary-gonadal axis,gonad function,fertilization,and/or early implantation.We review progress on the oral delivery of various agents for which laboratory studies have demonstrated efficacy in females and/or males and synthesize progress with the development and/or use of synthetic steroids,plant extracts,ovarian specific peptides,and immunocontracep-tive vaccines.There are promising results forfield application of synthetic steroids(levonorgestrel,quinestrol),chemosterilants(4-vinylcyclohexene diepoxide),and some plant extracts(triptolide).For most fertility control agents,more research is essential to enable their efficient and cost-effective delivery such that rodent impacts at a population level are mitigated and food security is improved.

Unwanted and unintended effects of culling: A case for ecologically-based rodent management

In this study, the ecological effects of culling programs are considered in the context of rodent pest management.Despite the escalation of rodent problems globally, over the past quarter of a century there have not been many newdevelopments in culling programs directed at managing these populations. There is a strong reliance on broad scaleuse of chemical rodenticides or other lethal methods of control. The ecological consequences of culling programsbased on chemical rodenticides and bounty systems are considered. Although rodents cause tremendous economichardship to people on a continental scale, usually less than 10% of species cause substantial impacts. Indeed, manyspecies of rodent provide important “ecological services” and, given that culling programs rarely distinguishbetween rodent species, often the non-pest rodents are at grave risk. Rodent control is conducted with littleappreciation of what proportion of the population would need to be culled for a significant reduction in economicdamage. In Indonesian rice fields, once rodent densities are high then a reduction in yield loss from 30% to 15%would require more than 75% of the population to be culled;a reduction to less than 5% yield loss would requiremore than a 95% cull. The negative ecological consequences of culling can be better managed if the method isspecifically tailored to the species that need to be managed. A greater emphasis on ecologically-based rodentmanagement would assist markedly in reducing the unwanted and unintended effects of culling.

Ethyl-iophenoxic acid as a quantitative bait marker for small mammals

Bait markers are indispensable for ecological research but in small mammals,most markers are invasive,expensive and do not enable quantitative analyses of consumption.Ethyl-iophenoxic acid(Et-IPA)is a non-toxic,quantitative bait marker,which has been used for studying bait uptake in several carnivores and ungulates.We developed a bait with Et-IPA,assessed its palatability to common voles(Microtus arvalis),and determined the dose-residue-relation for this important agricultural pest rodent species.Et-IPA concentrations of 40 to 1280μg Et-IPA per g bait were applied to wheat using sunflower oil or polyethylene glycol 300 as potential carriers.In a laboratory study,common voles were offered the bait and blood samples were collected 1,7,and 14 days after consumption.The samples were analyzed with LC-ESI-MS/MS for blood residues of Et-IPA.Sunflower-oil was the most suitable bait carrier.Et-IPA seemed to be palatable to common voles at all test concentrations.Dose-dependent residues could be detected in blood samples in a dose-dependent manner and up to 14 days after uptake enabling generation of a calibration curve of the dose-residue relationship.Et-IPA was present in common vole blood for at least 14 days,but there was dissipation by 33–37%depending on dose.Et-IPA meets many criteria for an“ideal”quantitative bait marker for use in futurefield studies on common voles and possibly other small mammal species.

Like or dislike:Response of rodents to the odor of plant secondary metabolites

Rodents,including common voles(Microtus arvalis)and house mice(Mus musculus)cause immense pre-harvest and post-harvest losses.Therefore,developing methods that mitigate these losses while maintaining their role in ecosystems is a priority.Several plant secondary metabolites(PSM)which significantly reduce food intake of both species under laboratory conditions have been identified.However,before these can be used in rodent pest management,they must be tested under more natural conditions where other food sources are available.In this study,the odors of 4 PSMs were evaluated for their repellent effects in experiments conducted in semi-natural enclosures.Soil treated with PSMs or untreated soil(experimental control)was placed in an underground box containing food(rolled oats).We quantified the number of visits to each box and could demonstrate that all 4 PSMs reduced the number of visits to treatment boxes in both rodent species.For common voles the combination of methyl nonyl ketone+black pepper oil was the most repellent PSM.House mice made fewer visits to all PSM boxes;boxes with the anthraquinone were visited least.Furthermore,house mice consumed less food from boxes containing soil treated with all 4 PSMs.Our results suggest that PSMs are repellent in murid and microtine rodents under semi-field conditions.In addition,the future use of PSM odors for repelling both pest species,especially house mice,seems promising.Further investigations with other PSMs,different concentrations as well as alternative application methods are needed to repel common voles from attractive crops.

Response of small rodents to manipulations of vegetation height in agro-ecosystems

Some small mammal populations require human interference to conserve rare or threatened species or to minimizeadverse effects in plant production. Without a thorough understanding about how small rodents behave in theirenvironment and consideration of how they react to management efforts, management will not be optimal. Socialbehavior, spatial and temporal activity patterns, predator avoidance and other behavioral responses can affect pestrodent management. Some of these behavioral patterns and their causes have been well studied. However, theirimpact on pest rodent management, especially for novel management approaches, is not always clear. Habitatmanipulation occurs necessarily through land use and intentionally to reduce shelter and food availability and toincrease predation pressure on rodents. Rodents often respond to decreased vegetation height with reducedmovements and increased risk sensitivity in their feeding behavior. This seems to result mainly from an elevatedperceived predation risk. Behavioral responses may lessen the efficacy of the management because the desiredeffects of predators might be mediated. It remains largely unknown to what extent such responses can compensateat the population level for the expected consequences of habitat manipulation and how population size and cropdamage are affected. It is advantageous to understand how target and non-target species react to habitatmanipulation to maximize the management effects by appropriate techniques, timing and spatial scale withoutcausing unwanted effects at the system level.

Integration of ecology and biology for the management of rodents:International perspectives 3

This special issue of Integrative Zoology is the third and final one in a series of issues containing papers presented at the Third International Conference on Rodent Biology and Management(ICRBM).The conference was held in Hanoi,Vietnam in August 2006 and focused on the areas of rodent biology,ecology and management(for details,please the summary report by C.J.Krebs see Integrative Zoology,1(4),194–195).The 1st ICRBM was held in Beijing,China,in 1998.The 2nd ICRBM was held in Canberra,Australia,in 2003.Papers of these two conferences were also published(Singleton et al.1999;Singleton et al.2003).This special issue contains a diverse range of papers examining rodents in urban environments,rodent behaviour and biology,and rodents in agricultural systems.

Integration of ecology and biology for the management of rodents: International perspectives 1

The papers presented in this special issue of Integrative Zoology(and over the next two issues)were mostly presented at the Third International Conference on Rodent Biology and Management(ICRBM)that was held in 28 Aug−1 Sept 2006 in Hanoi,Vietnam(for a summary of the conference,see the summary report by C.J.Krebs in Integrative Zoology,1(4),194–195).The conference attracted an international audience of 130 participants from 35 countries,with a good mix of developed and developing countries,and students and researchers,with a particular emphasis on supporting scientists and students from developing countries.The conference provided an opportunity for all participants to refresh and update their knowledge of scientific,technical and extension developments in the field of rodent biology.There were approximately 110 spoken papers and 50 posters over the 4 days of the conference.

Integration of ecology and biology for the management of rodents: International perspectives 2

Most papers presented in this, the previous and thenext special issue of Integrative Zoology were presentedat the 3rd International Conference on Rodent Biologyand Management (3rd ICRBM) that was held in earlyAugust in Hanoi, Vietnam 20061 . The conference attractedan international audience of 130 participants from35 countries and provided an opportunity for all participantsto refresh and update their knowledge of scientific,technical and extension developments in the field ofrodent biology. There were about 110 spoken papers andabout 50 posters. The three main themes of the conferencewere (1) rodent biology, (2) rodent ecology, and (3)rodent management.