Comparative assessment on rodent impacts and cultural perceptions of ecologically based rodent management in 3 Afro-Malagasy farming regions

Rodents generate negative consequences for smallholder farmers in Africa that directly impact household and livestock damage,food security,and public health.Ecologically Based Rodent Management(EBRM)seeks sustainable solutions for the mitigation of rodent damage through assessments of rodent population dynamics,agro-ecosystems,and socio-cultural contexts.We adopt a comparative approach across 3 rural Afro-Malagasy smallholder farming regions in South Africa,Tanzania,and Madagascar to assess the household impacts of rodent pests and current perceptions and preferences associated with several rodent control measures.We conducted focus group questionnaires and interviews in different study site locations.Rodents assert multiple impacts on Afro-Malagasy farmers demonstrating recurrent and emerging agricultural and household costs,and public health impacts.We identify a significant knowledge gap in educating communities about the application of different EBRM approaches in favor of acute poisons that are perceived to be more effective.Cultural issues and taboos also have a significant impact on the social acceptance of rodent hunting as well as biological control using indigenous predators.We advocate for an enhanced investigation of the socio-cultural beliefs associated with different rodent practices to understand the factors underlying social acceptance.A collaborative approach that integrates the perspectives of target communities to inform the design of EBRM initiatives according to the specific agro-ecosystem and socio-cultural context is necessary to ensure programmatic success.

Social and cultural dimensions of rodent pest management

Rice production in Vietnam is threatened by rodent pests, with a significant increase in impact reported from 1990through to the early 21st century. Pre-harvest rice losses are typically 5–10%, with losses of >20% occurring insome years in some regions. Farmers’ rodent control practices are generally reactive and rely essentially on chemicaland physical methods. Ecologically-based rodent pest management (EBRM) was developed in the late 1990s tomanage rodents in rice-based farming systems in Vietnam and other parts of South-East Asia. EBRM combinesboth cultural and physical rodent management practices such as synchrony of cropping, short 2-week rat campaignsat key periods in key habitats, increasing general hygiene around villages, and use of a communitytrap-barrier system. Although EBRM has been reported to be economically profitable, the successful adoption ofthis set of technologies requires community participation. In this paper we address issues relating to the adoptionand sustainability of EBRM in lowland irrigated rice fields in the Mekong Delta in Vietnam. We particularly explorethe social and cultural mechanisms involved in maintaining community participation to further understandthe conditions under which EBRM works and does not work. Positive indications of sustained use of community-based EBRM include: a policy pronouncement from the prime minister directing the use of integrated rodentmanagement;the use of existing cooperatives for developing community actions;budgetary allocation fromprovincial and local governments;diffusion of EBRM to provinces in the south and north that are not involved infarmer participatory field trials;and the adoption of EBRM by a non-governmental organization, World VisionVietnam, in their area-development programs.

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.

Impact of contraceptive hormones on the reproductive potential of male and female commensal black rats (Rattus rattus)

The black rat is considered one of the world’s top pests.With increased restrictions on rodenticides,new alternatives to manage rats are urgently needed.Research on the use of contraceptive hormones,levonorgestrel(LE),and quinestrol(QU),have been evaluated against some rodent species,and this research is thefirst study to assess these on black rats.Hormones were incorporated into rodent bait at 10 and 50 ppm concentrations singly and in combination(EP-1).Groups of 10 animals of each sex were fed the baits over 7 days.Lower bait consumption was observed with slight body mass reductions.On dissection,it was observed that the uterus was in a state of edema and male reproductive organs weighed less with reduced sperm counts/motility.The 2 most promising baits,50 ppm QU and EP-1,were used to assess impact on pregnancy and litter size.Pregnancy was reduced from 70%success when both males and females consumed untreated bait,down to 30%when males had consumed contraceptive bait but females had not,and down to 0%when females had consumed contraceptive bait,regardless of whether they had paired with a treated or untreated male.Litter size in the untreated pairs was 8 pups,but only 4 pups in those cases where the male only had consumed the contraceptive.Further studies should investigate how long the effect lasts and its reversibility.Field studies at the population level may also shed light on the practicality of using contraceptive baits for black rats in different habitats.

Impact of fertility versus mortality control on the demographics of Mastomys natalensis in maize fields

The multimammate mouse,Mastomys natalensis,is the most common rodent pest species in sub-Saharan Africa.Currently,rodenticides are the preferred method used to reduce the population of rodent pests,but this method poses direct and indirect risks to humans and other non-target species.Fertility control is a promising alternative that has been argued to be a more sustainable and humane method for controlling rodent pests.In this study,we compared the effectiveness of fertility control bait EP-1(quinestrol(E)and levonorgestrel(P),10 ppm)and an anticoagulant rodenticide bait(bromadiolone,50 ppm)on the population dynamics of M.natalensis in maizefields in Zambia during 2 cropping seasons.M.natalensis was the most abundant species in maizefields(77%of total captures).Fertility control reduced the number of juveniles and suppressed population growth of M.natalensis at the end of the 2019–2020 cropping season.The population density initially decreased after rodenticide treatment,but the population rapidly recovered through immigration.None of the treatments influenced maize damage by rodents at germination(F2,67=1.626,P=0.204).Applying the treatments during the maize seeding time was effective at suppressing population growth at the end of the cropping season than application the month before maize seeding.This research indicates that a single-dose delivery of EP-1 and rodenticide have comparable effects on the population dynamics of M.natalensis.Thesefindings are important in developing fertility control protocols for rodent pest populations to reduce maize crop damage and improve yields.

Reproductive responses of rice field rats(Rattus argentiventer)following treatment with the contraceptive hormones,quinestrol and levonorgestrol

The ricefield rat,Rattus argentiventer,is a significant pest of rice in Southeast Asia.Fertility control methods have the potential to provide safe and effective alternatives to control methods that often include indiscriminate use of rodenticides or electric barriers.The aim of this laboratory study was to assess uptake of bait coated with different concentrations of the contraceptive hormones,quinestrol(E)and levonorgestrel(P),delivered alone and in combination(i.e.EP-1)and determine the short-term effects on reproductive parameters of adult male and female R.argentiventer.In Experiment 1,2 concentrations of E,P,and EP-1(10,20 ppm)were fed to groups of wild-caught rats for 7 days.In females,both E and EP-1 induced uterine edema.In males,EP-1 reduced epididymis and seminal vesicle weights and lowered sperm motility.However,these responses were inconsistent due to low bait acceptance,especially with increasing concentrations.In Experiment 2,EP-1(0,20,50,100 ppm)was administered by oral gavage daily for 7 days to male R.argentiventer.There were significant reductions in epididymal and seminal vesicle weights for all oral doses of EP-1,in sperm counts for the 50 ppm dose,and in sperm motility for the 20 and 50 ppm doses compared to the control group.To select the optimum dose of EP-1,we must address the poor acceptance of contraceptive-coated baits by ricefield rats.Further research is required to improve the palatability of EP-1 and to test its uptake underfield conditions.