2.2.1. The Ethiopian EBRM Experience
In rural areas, some EBRM programs have been tested. In the Amhara Region of Ethiopia, MetaMeta, a Dutch social enterprise working with smallholder farmers in several countries, introduced an EBRM package [
26,
27] in 2019 for smallholder mixed cropping systems (growing wheat, barley and potato coupled with animal husbandry cultivating in small plots of land, on average ranging from as little as 0.5 to a few hectares). Prior to the introduction of EBRM, farmers and extension workers claimed severe rodent damage (>25%) (our unpublished data). Long before the EBRM introduction, farmers in the region had already organized into 63 Watershed User Associations (WUAs), registered under the regional government and are responsible for watershed management (mainly soil and water conservation practices) as a community, covering a total area of about 120,000 ha. Watershed groups involve all farmers who own adjacent crop fields and grazing lands in a particular watershed (catchment) area. These groups had a well-organized system in place and were best suited to operating community based EBRM at an appropriate scale for rodent management. The first and most important part of the EBRM activities was to take time for training and action planning co-constructed with the WUA committees, who then passed it on to all their members. In action planning they incorporated the timing of the EBRM actions in the lean season (i.e., when rodent populations are still at lower density) and the importance of collective action (e.g., they made by-laws that a household who did not join in a collective activity such as flooding rodent burrows, would pay a penalty). Because there was already established strong sense of community via the WUA, this was quite effective.
The activities incorporated into the EBRM package encompassed a range of measures, including (i) maintaining loose soil and water conservation structures, with a specific focus on stone bunds and terraces (which previously believed to provide shelter for rodents), (ii) clearing grasses and bushes in the vicinity of these bunds and terraces to create an open strip of land measuring 1-2 meters that enhance the visibility of rodents to their natural predators, (iii) implementing deep ploughing techniques to disrupt rodent habitats and burrows, (iv) employing strategies such as flooding and plugging rodent holes and burrows to curtail their population, (v) establishing stone traps to kill rodents, (vi) utilizing domestic cats, predominantly within homesteads, as a natural predator of rodents, and (vii) storing grains in locally made, rodent-proof storage structures to safeguard against rodent infestations.
These activities were combined with the application of a newly developed bio-rodenticide (a plant origin product proven to toxify rodent pests, our unpublished data waiting for patenting procedures for publication) implemented in the form of campaigns in the watershed areas, where all members of the watersheds were involved, starting from the time of land preparation to harvesting. In close collaboration with rodent scientists, MetaMeta developed the bio-rodenticide (BR) using extracts derived from a combination of two locally available plant species, with no chemicals or additives used during the BR formulation, which has been tested in the form of a powder delivered as bait mixed linseed [
28]. Its palatability, efficacy and potential harm to non-target species and the environment have been tested in the laboratory in Ethiopia. The palatability and efficacy tests were done on three rodent species (
Arvicanthis niloticus, Mastomys awashensis, Rattus rattus), under controlled laboratory condition, resulting in cumulative average mortality rate of ≥ 74% at 96 hours. Furthermore, the median lethal dose (LD50) for combination, dosed at 120 mg/g was 11.35g. Pending publication of the full results in a subsequent paper, our independent post-implementation survey involving participants from the watershed campaigns indicated that farmers perceived that rodent damages had been cut by a magnitude of up to 50% after two years of EBRM practicing. Moreover, the survey also indicated that through horizontal learning (a form of knowledge exchange and skill sharing that occurs within a community or among neighboring communities through a peer-to-peer approach), the uptake of the EBRM practices saw an increase of up to threefold in the neighboring watersheds that were not initially included in our EBRM campaigns. This suggests that the knowledge and success of these initiatives have spread effectively within the local agricultural community, benefiting a broader region beyond the project’s initial scope. The demand for the BR has increased significantly and to meet this increased demand and empower local entrepreneurs, about a dozen women small-scale enterprises (SMEs) have been trained by MetaMeta in 2020 and 2021 to produce package and sell the BR to fellow farmers at local scale at an affordable price. The production cost of the BR by the SMEs was about €1.50 per 250g jar. Furthermore, in comparison, in northern Ethiopia, farmers typically spend an annual average of €3-12 per hectare on pesticides [
29]. The authors also highlighted that farmers are willing to spend up to €9 to purchase a kitten as a preventive measure against stored-grain damage by rodents. In sub-Saharan Africa, farmers are willing to pay €3-10/ha for effective rodent management products per cropping season [
30].
Unlike synthetic rodenticides, BRs are inherently less harmful to the environment and non-target species since their active ingredients are largely volatile and quickly degradable, hence less persistent in the food chain and less dangerous for the environment (see [
31] and references therein). Although this probably deserves rigorous investigations, unlike synthetic chemical rodenticides, BRs usually are composed of a complex panel of co-acting molecules that work together to toxify rodents. This makes them less prone to the development of resistance against them. Efforts are underway to ensure wider use of the BR in Ethiopia as well as to extend this innovative approach to other African countries. There is enormous scope to make EBRM the standard rodent management method in Ethiopia and beyond as it holds great promise for sustainable and environmentally friendly pest management practices, benefiting both agriculture and the broader ecosystem.
2.2.2. Opportunities for EBRM in Sahelo-Sudanian Western Africa
In West Africa, such experiences in the realm of EBRM are almost non-existent, although a few isolated attempts have begun to provide elements that could contribute to integrated EBRM strategies. For instance, the traditional pitfall traps, locally called “Kornaka” traps, used by Sahelian farmers, appear to be promising to reduce pest gerbil populations in extensive pluvial millet fields in Central Niger. As evidence, during a brief trial, 37 captures were made in just three nights using 49 Kornaka traps, resulting in a capture rate of 25.2%. In comparison, 22 captures were achieved in five nights with 256 locally-made wire mesh traps, with a capture rate of only 1.7%. This illustrates that the Kornaka traps were 15 times more effective than the wire mesh traps [
32].
Additionally, in response a to a shortage of chemical rodenticides, Crop Protection officers in Ogo (Matam, Senegal) experimented pitfall traps during a participatory farmer action that lasted over 10-15 days in four localities in 2021 (B. Diouf, pers. comm., Feb. 2022). This small scale, preliminary demonstration resulted in notable rodent captures and was perceived as a promising method by most participants. However, the effectiveness of this method has not been precisely quantified, and some farmers expressed concerns about the labor intensity of this method compared to the relatively straightforward application of synthetic chemical rodenticides (B. Diouf, pers. comm., Feb. 2022). The additional labor requirements raised concerns, particularly in comparison to experiences in Asia [
33].
In Northern Senegal, through a rigorous decade-long rodent monitoring in agricultural fields and ongoing collaboration with crop protection experts, substantial progress has been achieved in the understanding of rodent related challenges and the potential for implementing EBRM [
34,
35]. Notably, this research has unveiled key insights, such as the identification of specific agronomic and physical factors within irrigated rice fields that strongly favor rodent populations. These factors include features like accumulations of thorn bushes used as hedges (see Fig 1 A) and the presence of densely vegetated dikes, bunds, and irrigation canals (refer to Figs 2 A-B). In terms of risk assessment, estimated by the Adjusted Odds Ratio, the abundance of each of the two main rodent pests affecting rice crops (
Mastomys huberti and
Arvicanthis niloticus) has shown a significant increase associated with environmental factors over a decade of monitoring in the Delta of River Senegal [
34]. For each single additional percentage of vegetation cover (for an average cover estimate of 67.4% and a range of 3.1% – 97.5% over a total of 267 sampled fields), the factor of increase stands at 1.02 [
34]. Pest rodents also exploit uncultivated parcels or edges of fields, where they find shelter and reproduce before invading rice fields [
34]. This underscores the potential benefit of improved land preparation and management of fallow lands adjacent to cultivated fields to mitigate rodent infestation and associated damages. Conversely, there are situations that appear to be less favorable to rodents, corresponding to those where shelters are rare and vegetation are well-controlled on dikes and other structures (Figs 2 C-D).
From these observations, several elements of EBRM can be proposed (see for more information [
13]). These may include replacing hedges made from thorny bush branches and random shrubs with tightly woven barriers made from materials like fishnets, recycled greenhouse sheets, or braided used drip pipes (as already practiced by some farmers), or employing more durable options such as wire mesh or barbed wire (refer to Figs 1 B-F). Other potential measures include activities such as mowing grass on dikes and irrigation channels, refraining from planting crops on dikes, crop rotation, composting of crop residues, and implementing minimal tillage practices targeting rodent burrow systems following crop harvests.
The recurrence of major damages to food crops since the 1970’s, caused by recurring events of particularly high rodent pest abundances, has led West African states and/or international institutions to repeatedly call external expertise for assessing the critical situation and propose sustainable strategies for rodent management [
36,
37,
38,
39,
40]. The rodent outbreak observed in the Senegal River valley during 2020-2021 is very illustrative of how the lessons that could have been learned from historical events and the wealth of scientific knowledge accumulated over the years have yet to be translated into concrete, effective, and sustainable management measures. Although it is likely too late the FAO took for the first time an interdisciplinary approach, integrating combining socio-economic, biological, and ecological perspectives [
35].
Of the total area of 111,643 ha cultivated with rice, 14 to 37% were reported to have been affected by rodents, depending on the region. This translates to an estimated loss of around 84,000 tons of paddy rice for a single cropping year, or 6 to 35% of the total expected rice production, depending on the region. The production loss was estimated at €26.5 million (ca. US
$ 31.4million in 2020-2021), directly affecting nearly 40,000 households or 270,000 people, which accounted for 11 to 14% of the population of these regions [
35]. Subsequent appraisals have outlined a lack of expertise and logistical constraints in national Crop Protection services, which present opportunities for targeted interventions.
In Senegal and Mauritania, Crop Protection officers have recently been trying to raise awareness among farmers, to encourage them carry out preventive measures against rodent pests in their fields. However, there is a growing need for these actions to be better organized and implemented at a larger scale. These initiatives should ideally be incentive-based and accompanied by thorough follow-up assessments to gauge their effectiveness. Recently, an integrated rodent management strategy has been formulated in Mauritania [
41]. Recognizing the importance of these efforts, the FAO has extended its support by launching two intervention projects in Mauritania and Senegal. These projects aim to increase awareness among farmers about the risks associated with the use of synthetic rodenticides for rodent control. Instead, they promote the adoption of alternative integrated management strategies based on a deep understanding of rodent population dynamics, both in terms of spatial distribution and temporal fluctuations.
An illustrative example of actions implemented in 2022 in Mauritania involved mechanical/physical management methods such as clearing the vegetation used as hiding places by rodents in dykes in rice fields, followed by the installation of mosquito nets on the dykes over rodent burrows, and then the mechanical exclusion of rodents trapped by the mosquito nets while flooding of burrows (Fig 3); and use of pitfall traps. To support these efforts, national and regional authorities have introduced strong incentives where the allocation of inputs, such as fertilizers, are lined to farmers’ active participation in rodent management activities. Additionally, the authorities have considered imposing fines for those who refuse to participate.
In Mali, the Rodentology Laboratory of the Institute of Rural Economics is currently actively engaged in conducting practical research activities in rural areas in line with public policies. They aim to evaluate the impact of four distinct rodent management methods on agricultural yields in the Baguineda (Mali) irrigated rice farming area (i.e., optimized chemical control, trapping sessions conducted in conjunction with collective actions implemented by farmers prior to the annual peak in rodent abundance, leveraging the repellent effect of predator odors, testing the efficacy of a local plant identified as potentially toxic to rodents based on their traditional knowledge).
Other innovative methods that have been developed in Southeast Asia and tested at small scale in East Africa, may have a promising future in Western Africa. For example, the community trap barrier system (cTBS) is an in-field rodent management method that can be used by irrigated rice farming communities [
42]. It involves the establishment of a rectangular "trap crop" three weeks before the rest of the fields are planted so that rodents from the surrounding areas are attracted to it. This "trap crop" is fenced with plastic sheeting which has multiple holes through which rodents can pass, and rodents are trapped using multiple-capture traps set along the holes. Field studies in irrigated rice cropping systems in Southeast Asia have shown that this method reduces the abundance of rodents over a large area surrounding the “trap crop” which reduces damage and increases yield [
43,
44]. It has been shown in Tanzania that a 20m x 20m cTBS significantly reduces rodent abundance over an area of up to 16 ha of irrigated rice fields, leading to an increase in rice yield by 41% [
45]. A simplified variant of cTBS, known as LTBS (Linear Trap Barrier System), has been tested in Asia [
44,
46], and a pilot study is currently underway in the Senegal River delta [
47]. LTBS comprises a stretch of plastic fencing with a minimum length of 100m long, which is partly buried underground to a depth of a few cm to deter rodents from tunneling underneath. Above ground, the fencing stands at a height of 60-70 cm. LTBS is installed to intercept rodent movements into or within crop fields by exploiting the innate tendency of certain rodent species to move along physical barriers, such as walls or fence [
44]. Unlike cTBS, LTBS does not require setting up “trap crops” to attract rodents. To the best of our knowledge, such alternative rodent management methods have not been formally tested in West Africa and their impact in terms of food production, health and environmental risk still needs to be quantified. Note that both cTBS and LTBS are likely to be most effective in irrigated rice fields and may encounter limitations when dealing with agile climbing rat species. Therefore, it is crucial to understand the specific behavior of rodent species in the fields under consideration. There are also other promising methods, such as the use of improved hermetic grain storage bags (e.g., International Rice Research Institute (IRRI) bags, Purdue Improved Crop Storage (PICS) bags), which provide a better grain storage opportunity to farming communities against rodent and insect damages, limit spoilage and reduce aflatoxin contamination [
48,
49,
50].
Importantly, while some rodent management actions may be efficient to decrease rodent abundances and mitigate their deleterious impacts [
2,
3,
4,
5,
6,
7,
8,
9,
10], they may inadvertently conflict with crucial socio-economic aspects. To ensure local suitability and adoption, first, it is imperative that the direct costs of implementing EBRM are lower than the overall impacts caused by rodent infestations. This also holds true for the perceived gains and losses by farmers, not only their monetary values. Second, the timing of the management shall be aligned with the local agricultural calendar in order to facilitate mobilization of resources for the task. Besides, to ensure greater effectiveness, the management actions should be initiated during periods when the rodent population is at a low density (such as the lean period before they reproduce), rather than waiting until outbreaks occur when the population has become too large to control. Third, one should be very cautious about the interrelationships between rodent management actions aligned with the cropping calendar and the cattle breeding systems, especially in the Sahelian region where pastoralism is widespread and critical activity, encompassing food, cultural, and economic aspects. For instance, in the Sahelian pastoralist livestock production system, grazing stubble plays an important role and, provided that overgrazing is avoided, the practice greatly contributes to soil fertility by adding manure. Moreover, livestock can remove spilled grain and trample the ground upsetting rodent burrows. In such a context, post-harvest actions such as field clearing and tillage, while effective for reducing pest rodent populations, may have detrimental effect on conservation agricultural practices and on domestic animals, including meat, milk, and leather production. Some cattle breeders also mentioned the risk of having cattle wounded by pitfall traps (i.e., Kornaka) while wandering at night (K. Hima, pers. obs.). To minimize such risks and address potential conflicts with local residents, grazing stubble could be timed and incorporated into other activities of field clearance and pitfall trap may be covered (i.e., closed) during periods of cattle grazing. In summary, the success of EBRM in this region will strongly depend upon finding a delicate balance between socio-economic gains and investments, taking into account the interplay between rodent management, agriculture, and cattle breeding systems.