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The bioeconomics of controlling an African rodent pest species

Authors:
Anders Skonhoft at Norwegian University of Science and Technology
Anders Skonhoft
Herwig Leirs at University of Antwerp
Herwig Leirs
Harry P. Andreassen at Hedmark University College
Harry P. Andreassen
Loth Mulungu at Sokoine University of Agriculture (SUA)
Loth Mulungu
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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.
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2006; Skonhoft et al - Bioeconomics mastomys; Env Dev Econ 11, 453-4
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... Rodent pests damage maize crops before and after harvest (Skonhoft et al., 2006;Swanepoel et al., 2017). Mostly, rodent pests damage maize crops during the germination (Mulungu et al., 2005) and maturation stages (Mulungu, 2017). ...
Vegetation cover and food availability shapes the foraging activity of rodent pests in and around maize fields
Article
  • Jan 2023
Evidence-based information for smallholder farmers on where and when to conduct rodent management is vital given that most are resource poor and depend on agriculture for food and income. However, there is scarce information on how the foraging activity of rodent pests changes over agricultural cropping seasons. We used the concepts of giving-up-density (GUD) and landscape of fear to monitor how the foraging activity of rodent pests changes in and around maize (Zea mays) fields over the cropping season. We tested the hypothesis that the foraging activity of rodent pests will be influenced by vegetation cover, perceived predation risk and food availability. Mastomys natalensis was the dominant species in all maize fields (n = 3, 87.05 % of the total captures). We observed that the foraging activity of rodents was influenced by vegetation cover and food availability. During the germination stage, rodent activity in the natural habitat and along the border was higher than inside the maize fields. During land preparation, planting, weeding, maize tasselling, maturity, and post-harvest stages, there was no difference in the foraging activity in and around the maize fields. During the harvest stage, the foraging activity was higher in the maize fields than along the border and in the natural habitat. These results can be used to guide smallholder farmers where and when to focus rodent control measures during different stages of the cropping season. An additional approach would be to develop strategies that could potentially increase rodent fear perceptions in cropping landscapes.
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... In Tanzania alone, they are responsible for 15% of the annual yield loss of maize, which corresponds to a loss of $45 million (enough to feed 2 million people for a whole year), but crop losses can increase up to 80% during outbreaks of M. natalensis (Mwanjabe et al. 2002;Stenseth et al. 2003;Mulungu 2017). The ecology of M. natalensis has been studied extensively over the last 30 years (Telford 1989;Leirs et al. 1990Leirs et al. , 1993Leirs et al. , 1994Leirs et al. , 1997Julliard et al. 1999;Sluydts et al. 2007Sluydts et al. , 2009Mlyashimbi et al. 2019;Mayamba et al. 2020a) which has been shown to be useful in the control and management of rodent-based damage (Singleton et al. 1999;Skonhoft et al. 2006). They are an excellent model system to investigate the effect of personality on viral infection risk, either by influencing the hosts' encounter rate with the virus and/or affecting infection susceptibility by underlying co-infection patterns. ...
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... There are cases where the relationship between damage and rodent density is well worked out. Tanzanian researchers and their overseas collaborators have approached the development of control of M. natalensis in maize through studies of population ecology and density-damage relationships in order to reduce populations to below 20 ha −1 (Skonhoft et al., 2006). This has led to a prediction model for rodent population dynamics and the economics of control strategies for the whole region (Leirs et al., 1996). ...
Rodents in agriculture and forestry.
Chapter
  • May 2015
This updated 2nd edition, two decades after the publication of the first edition, combines information from the latest scientific research on rodent pests and their control. It includes 19 chapters discussing: the natural history of rodents and preadaptations to pestilence; commensal rodents; rodents in agriculture and forestry; rodents as carriers of disease; non-chemical and non-lethal chemical control methods, with special reference to food stores; chemical control methods; laboratory evaluation of rodenticides; field evaluation of rodenticides; resistance to anticoagulant rodenticides; damage assessment and damage surveys; rodent control in protection of humans and animal health; rodent control in temperate field crops and forestry; rodent control in tropical field crops; sociology and communication of rodent management in Developing Countries; ethics in rodent control; environmental impacts of rodenticides; monitoring rodenticide residues in wildlife; rodent control and island conservation; and rodent control 20 years since the publication of the first edition. This book is essential reading for all those involved in rodent pest control, including researchers, conservationists, practitioners and public health specialists.
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... Since rodent pests have been causing deleterious impacts or losses on cocoa from time immemorial, it can be said that rodent control is inevitably as old as the rodent menace itself. The regulation of pest rodents does have both an economic as well as ecological constituent having a dynamic interaction [74]. The links that exist between these constituents are characterized by the control plans impacting the death of rodents including their damages on cocoa. ...
Impacts of Rodents Pests on Cocoa (Theobroma cacao L): A Mini Review
Article
  • Jun 2021
Aim: To assess the impacts of rodent pests on Cocoa (Theobroma cacao) production and productivity. Rodents belong to the mammalian order that is widely distributed globally. Their adaptive potential and capability to face changing environments even when instigated by anthropogenic activities is quite amazing. Also, their importance as vital links in food chain between species of plants and the predators thereby playing crucial roles within the ecosystem cannot be overemphasized. Rodents have been noted to cause ubiquitous damage to agricultural crops including cocoa. They can cause damage in crop fields from planting throughout harvest and storage. The damages caused by rodent pests mostly occur during the sensitive young seedling stage and just prior to harvesting. The pattern and the extent of damage by pest rodents depend upon the species, the intensity of infestation, the type and the growth stage of the crop, and the nature of the surrounding habitat. These damages caused by rodent pests could be direct through the consumption of cocoa beans or indirect through the biting, gnawing or scratching of pods which could range from slight to severe. The stern impacts caused as a result of rodent pest activities are not only felt in the quantity and quality of cocoa pods but also on the social maintenance as well as survival of those growing the crop. Despite the paucity of documented data as regards the kind, form as well as ferocity of rodent damage, it is highly expedient to re-evaluate the rodent pests’ impacts on the production of cocoa so as to update the very scarce available information whilst providing a basis for additional investigation.
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... Specifically, the control should be conducted between January and May when densities are low and when farming activities are at their lowest. Nevertheless, before launching any control activities, it would first be necessary to evaluate its cost-benefit ratio [63]. Indeed, it may happen that, below a certain threshold of pest density, the damage caused may be less costly than the control procedure itself. ...
Dynamics and Genetics of Gerbillus nigeriae in Central Sahel: Implications for Rodent Pest Control
Article
Full-text available
  • Dec 2019
Gerbillus nigeriae is a sand-dwelling and semi-arid adapted rodent species restricted to the West African Sahel where it causes extensive damages to cereal crops such as millet and sorghum. It also displays one of the most extensive floating chromosomal polymorphisms currently known in mammals, showing a non-random spatial distribution of diploid numbers (2N). We combined population dynamics and genetics to determine dispersal and mobility parameters of G. nigeriae in the species distribution range characterized by low 2N. To do so, we performed a three-year long population survey at Gangara, in the central east Niger. We used both time-dependent monitoring trough capture-mark-recapture (CMR) methods and genetic analyses performed on the 134 monitored individuals. CMR results showed low to very low population densities (maximum 27.5 individuals/ha) throughout the study. Abundance cycle was single-phased and strongly dependent on rainfall patterns. Mobility parameters showed very low individual mobility, with means of distance between successive (re) captures (DRS) and maximal distance between (re) captures (DMR) of 7.8 and 14.4 meters, respectively. Genetic analyses revealed significant isolation by distance as well as spatial structuration, thus confirming poor dispersal capacity. Our results are discussed in terms of rodent pest control in arid areas of Niger where cereal crops production is crucial for human food security.
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... They do, for instance, cause serious damage to crops (such as cereals, root crops, cotton and sugarcane) both before and after harvest. 3 Rodents typically have short gestation period, with high litter sizes and ability to become full pregnant again after a few days of delivery. These factors alone would ensure a high reproductive potential. ...
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... They do, for instance, cause serious damage to crops (such as cereals, root crops, cotton and sugarcane) both before and after harvest. 3 Rodents typically have short gestation period, with high litter sizes and ability to become full pregnant again after a few days of delivery. These factors alone would ensure a high reproductive potential. ...
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Farmer's perspectives of rodent pests' damage and management practices in Wenchi highlands, central Ethiopia
Preprint
Full-text available
  • Dec 2022
A study was conducted to obtain information about the knowledge, attitudes and practices (KAP) of farmers in Wenchi highlands on rodent damage and their management practices. Farmers (n=395) from four highland villages of Wenchi District were randomly selected and interviewed using a semi-structured questionnaire. Rodents were identified as major pests, and perceived negatively among farmers. There were significant variations in the type of damage (χ2=112.698, df= 3, p < 0.05) and crop types susceptibility to rodent pest attack (χ2= 143.26, df = 3, P < 0.05). Crop damage (38.7%) and damage to human properties (27.9%) were the two dominant rodent related problems in the area. Barley was the most susceptible crop to rodent attack (57.5%). The occurrence of frequency of rodent pests and crop damage between the cropping stages also varied significantly. Most damage on barley crop (42.5%) occurred during the maturation stage. Farmers assessed and detected rodents damage by observing damaged seeds, damaged stores and rodent droppings in the storage, and stem cut of standing crops in the crop fields. None of the farmers have employed any management strategy in barley crop fields stating that this is practically impossible. In storage, farmers mainly use cats (53.73%) and trapping (22.64%) to control rodents. Detailed off-field rodent damage assessment, and community education for rodent management are recommended.
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Invasive rodents and damages to food stocks: a study in the Autonomous Harbor of Cotonou, Benin
Article
Full-text available
  • Jan 2020
Description of the subject. Rodents may be major pests to crops and stored food, thus threatening food security. Among them, invasive species such as rats and mice are of particular concern since they are disseminated globally following international trade. We investigated the small mammal assemblage within the international seaport of Cotonou, Benin, in order to determine the relative importance and distribution of native vs invasive rodent species, as well as to evaluate the amount and associated costs of rodent-induced damages on imported 'exported stored goods (here, rice).Objectives. Description of rodent assemblages within an African seaport, and evaluation of the associated damages on stored food stocks.Method. Rodent communities were described following trapping results while associated damages and costs were evaluated following a 25 days-long monitoring campaign and subsequent economic estimation of loss.Results. Our results show that invasive mice and rats are, from far, the most impacting rodents in the storage warehouses, and that the associated economic losses are quite large. Moreover, we point towards a few environmental management procedures that may greatly reduce the impact of rodents on stored goods.Conclusions. Damages and costs due to invasive rodents within the Cotonou Harbor are so that they justify financial investment in rodent population control.
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A REVIEW OF SUSTAINABLE INTENSIFICATION OF AGRICULTURAL TECHNOLOGIES IN THE WEST AFRICAN DRYLAND SMALL HOLDER FARMING SYSTEMS
Conference Paper
Full-text available
  • Dec 2016
In sub-Saharan Africa, there is significant concern about the potential impacts of climate change and future variability on the productivity of agricultural crops. Assessing the magnitude of such impacts on crop yields in the future remains challenging due to the confounding influence of other more potent drivers of change. In this study, we discuss yield projections generated under the Agricultural Model Inter-comparison and Improvement Project (AgMIP) for a distribution of farms and agricultural practices representative of the Koutiala district in Mali's cotton belt. Our analysis focused on two local sorghum genotypes (CSM335 'Ceblen' and CSM63E 'Jakunben') calibrated in three contrasted process-based models (APSIM, DSSAT, Samara) driven by the climate projections of five GCMs for the mid-century period (2040-2069) at 571ppm CO2 concentration. The results of the climate change projections indicate a consistent pattern of increase in the mean growing season temperatures and little or no change in precipitation with high agreement, which is expected for temperature but unusual for precipitation in that region. On the average, sorghum yields decline in the absence of any adaptation measures. Simple plant adaptation options such as lengthened crop duration and altered root distribution are usually sufficient to offset this decline. Simpler models such as Samara performed better at mimicking the observed distribution of yields than complex ones such as APSIM in data scarce environments. Randomization procedures required allocating farms across a discrete and limited sample of soil types and fertility management practices can however have a very significant effect on simulated yield distributions and on the uncertainty associated with yield projections.
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An early warning system for IPM-based rodent control in smallholder farming systems in Tanzania
Article
We conducted a four-year study in Tanzania to test a method for predicting outbreaks of Mastomys natalensis rats and verify whether such method, based on rainfall variability, could be used in an Integrated Pest Management strategy for rodent control. Temporal fluctuations in rodent numbers and breeding activity were monitored at four localities with different rainfall regimes. Breeding peaked towards the end of the main rainy season and continued into the dry period. When the short rains of October-January were unusually abundant and well distributed, reproduction started earlier and rodent numbers increased faster. Where abundant short rains were a normal condition returning every year, such effect was not clear. A method to assess rodent damage to germinating seedlings was found to be robust and can be used for monitoring rodent problems. Using this assessment technique, we showed that the effects of a single control action undertaken at planting time do not persist long enough to protect seedlings, probably due to quick reinvasion of the treated fields by rodents from the surroundings. These observations are formulated into a rodent control package whose steps are to predict rodent outbreaks, to warn farmers and the government of the outbreaks, and to organise control measures in advance.
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Productivity of Different Generations in a Population of Mastomys natalensis Rats in Tanzania
Article
  • Oct 1993
In Tanzania three different generation types can be recognized in Mastomys natalensis rats. The alpha-generation is born in the main breeding season and breeds in the next main breeding season. The beta-generation is born in the main breeding season but reproduces already after abundant off-season rainfall. Its offspring, the gamma-generation, is born in the off-season breeding period and breeds in the same year. Life histories of these three generation types are different. Generation alpha has a long growth stop, poor survival until breeding but up to six consecutive litters; generation beta has a short growth stop, a better survival until reproduction but breeds only once or twice. The gamma-generation, however, grows very fast and reproduces at young age. Through their daughters, the beta-generation thus produces more than seven times as much young as the alpha-generation before the end of the following year. The occurrence of these generation types partially explains the relationship between rainfall patterns and population fluctuations.
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Forecasting Rodent Outbreaks in Africa: An Ecological Basis for Mastomys Control in Tanzania
Article
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1. Rainfall data were collated for years preceding historical outbreaks of Mastomys rats in East Africa in order to test the hypothesis that such outbreaks occur after long dry periods. 2. Rodent outbreaks were generally not preceded by long dry periods. 3. Population dynamics of Mastomys natalensis rats in Tanzania are significantly affected by the distribution of rainfall during the rainy season. 4. All previous rodent outbreaks in Tanzania were preceded by abundant rainfall early in the rainy season, i.e. towards the end of the year. 5. A flow chart is constructed to assess the likelihood of rodent outbreaks up to 10 months beforehand, utilizing rainfall data.
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