Highlands Of Kenya Research Articles

Agricultural Monitoring, an Automatic Procedure for Crop Mapping and Yield Estimation: The Great Rift Valley of Kenya Case

Agricultural activities conducted in the Great Rift Valley of Kenya show a significant decline of productivity levels. This phenomenon is mainly related to limited availability of water resources, lack of supporting irrigation, and harvesting techniques ineffectiveness. Production risks reduction is closely related with a better use of water resources and a better understanding of the effects resulting from the multiple interactions between climate, agricultural vegetation, soil type, and crops management techniques. In this paper, a remote and automatic agricultural monitoring system is presented as an effective alternative to the most traditional in situ measurements and observations. We investigated the use of phenological information extracted from satellite imagery combined with crop calendar and supported by agro-ecological zoning (AEZ) in accurate crop classification and monitoring. Vegetation indices extracted from Landsat 8 imagery are capable to track the vegetation development through the year, then phenological profiles can be extracted and implemented into a multitemporal automatic classification process to detect agricultural areas and to discriminate among different crop species. The phenological profiles extracted by satellite imagery are compared with crop calendar data compiled by FAO for the area of interest. The classification procedure is supported by AEZs based on crop modeling and environmental matching procedures in order to identify crop-specific environmental limitations under assumed levels of inputs and management conditions. The FAO crop water productivity model AquaCrop is calibrated for wheat and maize yield mapping in the central highland of Kenya, handling both environmental and phenological data. The combined use of phenological data and AEZs results in a robust methodology with a classification overall accuracy of 91.35%. A good model performance is obtained relative to yield predictions, with R of 0.69 and 0.72.

Epidemiological risk factors for clinical malaria infection in the highlands of Western Kenya

BackgroundUnderstanding the complex heterogeneity of risk factors that can contribute to an increased risk of malaria at the individual and household level will enable more effective use of control measures. The objective of this study was to understand individual and household factors that influence clinical malaria infection among individuals in the highlands of Western Kenya.MethodsThis was a matched case–control study undertaken in the Western Kenya highlands. Clinical malaria cases were recruited from health facilities and matched to asymptomatic individuals from the community who served as controls. Each participant was screened for malaria using microscopy. Follow-up surveys were conducted with individual households to collect socio-economic data. The houses were also checked using pyrethrum spray catches to collect mosquitoes.ResultsA total of 302 malaria cases were matched to 604 controls during the surveillance period. Mosquito densities were similar in the houses of both groups. A greater percentage of people in the control group (64.6%) used insecticide-treated bed nets (ITNs) compared to the families of malaria cases (48.3%). Use of ITNs was associated with lower level of clinical malaria episodes (odds ratio 0.51; 95% CI 0.39–0.68; P < 0.0001). Low income was the most important factor associated with higher malaria infections (adj. OR 4.70). Use of malaria prophylaxis was the most important factor associated with less malaria infections (adj OR 0.36). Mother’s (not fathers) employment status (adj OR 0.48) and education level (adj OR 0.54) was important malaria risk factor. Houses with open eaves was an important malaria risk factor (adj OR 1.72).ConclusionThe identification of risk factors for clinical malaria infection provides information on the local malaria epidemiology and has the potential to lead to a more effective and targeted use of malaria control measures. These risk factors could be used to assess why some individuals acquire clinical malaria whilst others do not and to inform how intervention could be scaled at the local level.

Distribution, degree of damage and risk of spread of Trioza erytreae (Hemiptera: Triozidae) in Kenya

AbstractThe African citrus triozid (ACT), Trioza erytreae Del Guercio, is a destructive pest particularly on citrus, and vectors, “Candidatus” Liberibacter africanus (CLaf), which is the causal agent of the African citrus greening disease. Our study seeks to establish the distribution and host‐plant relationship of ACT across citrus production areas in Kenya. We also modelled the risk of spread using the maximum entropy modelling algorithm with known occurrence data. Our results infer that ACT is widely distributed and causes severe damage to four alternative host plants belonging to the family Rutaceae. The adults, immature stages (eggs and nymphs), galls and the percentage of infested leaves were significantly higher in shaded than unshaded trees. However, adult ACTs preferred Kenyan highlands to Victoria Lake and coastal regions. The average area under the curve of the model predictions was 0.97, indicating an optimal model performance. The environmental variables that most influenced the prediction were the precipitation of wettest quarter, precipitation of wettest month, mean diurnal range, temperature seasonality and mean temperature of the coldest quarter. The current prediction of ACT exceeded its existing range, especially in the Western, Nyanza, Central, Rift valley and Eastern regions of Kenya. The model predicted a contraction of suitable habitats for a potential spread in 2040 with an inland shift to higher altitudes in the cooler regions. The potential for further expansion to climatically suitable areas was more pronounced for the 2080 forecast. These findings provide relevant information to improve monitoring/surveillance and designing IPM strategies to limit its spread and damage.

Genetic variation of the most abundant forest‐dwelling rodents in Central Africa (Praomys jacksoni complex): Evidence for Pleistocene refugia in both montane and lowland forests

AbstractAimWe investigate the Plio‐Pleistocene evolutionary history of one of the most abundant rodents in Afrotropical forests. Specifically, we ask how their diversification was influenced by climate change, topography and major rivers.LocationTropical Africa: Lower Guinea (including Cameroon volcanic line; CVL), Congolia, Albertine Rift (AR), Kenyan highlands (KH).TaxonMurine rodents of the Praomys jacksoni complex.MethodsWe used 849 genotyped individuals to describe the overall diversity and spatial genetic structure across a majority of their known distribution area. The combination of one mitochondrial and three nuclear markers was used to infer dated phylogenies using Bayesian and maximum likelihood approaches. Genetic structure was further assessed by multispecies coalescent species delimitation. Current and past distributions of particular taxa were predicted using environmental niche modelling.ResultsThe complex is composed of five major genetic clades (proposed species). Two of them are restricted to specific habitat types (either montane forests of AR or wetlands in lowland forests along the Congo River), three others have wide geographic distributions and lower levels of ecological specialization. The earliest divergence is dated to the Plio‐Pleistocene boundary and is in accordance with the separation of AR forests and Guineo‐Congolian forests. Further diversification of the complex is associated with Pleistocene climate changes. Relatively stable refugia of suitable climatic conditions were identified in lowland Congolia (for two species currently distributed only in lowland forests) as well as in montane forests of CVL, AR, KH (playing the role of reservoirs of diversity). Large rivers, especially the Congo River, are important barriers to gene flow for most taxa, but probably were not the primary cause of differentiation.Main conclusionsThe evolutionary history of the complex was primarily affected by Pleistocene climate changes and diversification in forest refugia. There is little support for ecological parapatric speciation or the riverine barrier hypothesis.

Agricultural Productivity and Soil Carbon Dynamics: A Bioeconomic Model

AbstractWe examine the dynamic management of a soil resource—the issue at the core of both environmental and development challenges in developing countries. Our theoretical framework extends the traditional bioeconomic model of renewable resources to soil carbon management and investigates the effects of changes in agricultural practices on farmers' natural resource base and livelihoods. We parameterize the model using an eight‐year panel data set from an agronomic experiment and data from household and market surveys in the western Kenyan highlands. The optimal maize yields and soil carbon stocks are higher than those observed in the region. This divergence is partly explained by farmers' heterogeneous time preferences (with the implied discount rates of 5% to 25%), information barriers, and market imperfections. The steady‐state shadow price for soil carbon ranges from $95/Mg to $168/Mg, indicating a significant opportunity cost for soil mismanagement.

Agronomic biofortification of maize and beans in Kenya through selenium fertilization.

Deficiency in calcium, zinc, selenium, and iodine remains a major health issue in Africa. A selenium (Se) status survey conducted in central Kenya highlands revealed a high risk of dietary Se deficiency. This study investigates the effect of soil and foliar Se fertilizer application on Se concentration in maize and bean grains. It further tests the combination of Se fertilizer with phosphorus and nitrogen fertilizers, and with zinc and iodine fertilizers. Selenium fertilization results in a significant increase in Se concentration in grains. For the soil application, Se concentration increases on average by 3µgkg-1 in maize and by 10µgkg-1 in beans, for each gram of Se applied as sodium selenate. Foliar Se fertilization is more effective and increases Se concentration in grains on average by 18µgkg-1 in maize, and by 67µgkg-1 in beans. Total soil phosphorus/availability appears as an important factor influencing soil Se availability. Addition of phosphorus fertilizers positively affects the impact of Se fertilization in locations with low soil P, Fe, and Al. A Se + Zn + I fertilizer combination does not affect the impact on Se concentration in grains. Fertilizing beans alone is found to be more efficient compared to fertilizing only maize. In locations at high risk of dietary Se deficiency, foliar application at 10g Se ha-1 on beans or 31g Se ha-1 on maize is sufficient to achieve adequate daily dietary Se intake. The study points towards a multi-mineral agronomic biofortification, based on a site-specific biofortification strategy.

Controlling soil erosion in smallholder potato farming systems using legume intercrops

Soil and nutrient losses due to soil erosion are pronounced in potato growing areas of East Africa due largely to the rugged topography and high soil disturbance associated with potato cultivation. This study intercropped potato (Solanum tuberosum L.) with three grain legumes: lablab bean (Lablab purperous L.), garden pea (Pisum sativa L.) and climber bean (Phaseolus vulgaris L.) in runoff plots and assessed their impact on soil and nutrient losses in central Kenya highlands. Bare plots and sole potato stands were included as controls. Vegetal cover was measured at different potato growth stages while runoff and soil loss were quantified at every runoff generating event and used for nutrient analyses. Yields were expressed as potato equivalents (PEY) at the end of each season. Mean cumulative sediment yield decreased from 169 t/ ha in sole potato plots to 50–83 t/ ha in potato-legume intercropping, representing a reduction of 51–70%. The eroded sediment exported in large quantity the SOC (16.6–39.5 kg C ha−1 yr−1), N (5.5–29.8 kg N ha−1 yr−1), P (3.9–16.4 kg P ha−1 yr−1) and K (5.2–14.6 kg K ha−1 yr−1) and were consistently higher in sole potato plots relative to potato-legume intercropping. These losses occurred mainly at potato emergence following fertilizer application. Stronger associations of sediment nutrient enrichments was found with the micro-aggregates (250–50 μm) than with the macro-aggregates (>250 μm) pointing to the different degree of nutrient mobilization and distribution in eroded sediment. The PEY were significantly greater in potato-lablab bean system than in sole potato, while intercropping with garden pea and climber bean showed similar PEY to that of sole potato, suggesting that potato-lablab system may be preferred by the smallholder farmers. These results justify the need to intercrop potato with indeterminate legume intercrops, a strategy that must be done in a way guaranteeing high yield stability to the smallholder farmers.

Large Hive Beetles: An Emerging Serious Honey Bee Pest in the Coastal Highlands of Kenya

Surveys in Kenya have established the main arthropod pests associated with honey bees (Apis mellifera) to be small hive beetles, Aethina tumida (Coleoptera: Nitidulidae); Oplostomus haroldi and Opl...

Nitrogen release and synchrony in organic and conventional farming systems of the Central Highlands of Kenya

To match Nitrogen (N) supply to crop N demand, it is essential to understand N release and uptake patterns in different farming systems and crops. To assesses the dynamics of N released in organic and conventional systems and potential synchrony and asynchrony in crop N uptake, a study was conducted over three cropping seasons (potato, maize and leafy vegetables) at two sites in the Central Highlands of Kenya. Mineral-N release and synchrony were monitored in conventional and organic systems at high (recommended N, P, pesticides and irrigation) and low input (low N, P, pesticide use and rainfed) systems. Mineral-N release was assessed using in situ buried bags and N synchrony was measured by the daily differences in N fluxes. The percentage of N applied released during potato (38%) and vegetable (44%) cropping seasons were similar between systems. However, under maize strong temporal N immobilization from inputs occurred, particularly at Thika, related to the poor quality of manure and compost (lignin:N ratio > 13). In all systems, excess-asynchrony of available N was pronounced during vegetative stages and at harvest, while insufficient-asynchrony occurred at reproductive stages. During potato cropping season at Thika, Org-High showed highest positive N fluxes (> 20 kg N ha−1 day−1) at planting and tuber bulking stage. At early stages of maize and vegetables Org-Low and Org-High experienced up to 5 times larger negative N fluxes (insufficiency) compared to conventional treatments at Chuka site. The study recommends reducing N applications at planting and increasing N dosages at reproductive stages of crops.

Soil fertility inputs and tillage influence on maize crop performance and soil water content in the Central Highlands of Kenya

Rigorous land ploughing and cropping fertiliser treatment and mineral fertiliser combined with animal manure treatment) consistently enhanced maize crop growth and development as observed through enhanced chlorophyll content, plant height and yields. Application of soil fertility inputs significantly improved grain and stover yields except in the crop residue combined with animal manure and legume intercrop treatment (perhaps due to nutrients’ competition since Lablab has an intensive rooting system). Sole organic inputs enhanced soil moisture content in both sites. Emerging from the study, however, is the lack of advantage of minimum tillage over the conventional tillage, within the period under consideration. Thus, this study highlights the possibility of improving soil water holding capacity through application of organic inputs such as crop residues, Tithonia diversifolia and manure, either singly or in combination. It further underpins the uniqueness of an integrated approach to soil fertility and low soil moisture content in the tropical sub-humid regions experiencing erratic rainfallivity in the Central Highlands of Kenya due to low and declining soil fertility, inappropriate tillage methods, soil water scarcity and prolonged dry-spells. In this study, we assessed the effects of two tillage systems and soil fertility inputs on maize crop performance and soil water content. The research was carried out in Chuka and Kandara sites in the Central Highlands of Kenya for four seasons; long rains 2016, short rains 2016, long rains 2017 and short rains 2017. The experimental design was a split plot with tillage method (minimum and conventional) as the main treatments and soil fertility inputs as the sub-treatments: Sole mineral fertiliser, mineral fertiliser combined with crop residue, mineral fertiliser combined with animal manure, Tithonia diversifolia combined with phosphate rock (Minjingu), animal manure intercropped with Dolichos Lablab L. and a Control (conventional tillage with no inputs). Except for the control, and sole mineral fertiliser, crop residue was applied as mulch in all treatments. Based on the results, the treatments with mineral fertiliser (sole mineral fertiliser combined with mineral fertiliser treatment and mineral fertiliser combined with animal manure treatment) consistently enhanced maize crop growth and development as observed through enhanced chlorophyll content, plant height and yields. Application of soil fertility inputs significantly improved grain and stover yields except in the crop residue combined with animal manure and legume intercrop treatment (perhaps due to nutrients’ competition since Lablab has an intensive rooting system). Sole organic inputs enhanced soil moisture content in both sites. Emerging from the study, however, is the lack of advantage of minimum tillage over the conventional tillage, within the period under consideration. Thus, this study highlights the possibility of improving soil water holding capacity through application of organic inputs such as crop residues, Tithonia diversifolia and manure, either singly or in combination. It further underpins the uniqueness of an integrated approach to soil fertility and low soil moisture content in the tropical sub-humid regions experiencing erratic rainfall.

Evolutionary insights of Bean common mosaic necrosis virus and Cowpea aphid-borne mosaic virus.

Plant viral diseases are one of the major limitations in legume production within sub-Saharan Africa (SSA), as they account for up to 100% in production losses within smallholder farms. In this study, field surveys were conducted in the western highlands of Kenya with viral symptomatic leaf samples collected. Subsequently, next-generation sequencing was carried out to gain insights into the molecular evolution and evolutionary relationships of Bean common mosaic necrosis virus (BCMNV) and Cowpea aphid-borne mosaic virus (CABMV) present within symptomatic common bean and cowpea. Eleven near-complete genomes of BCMNV and two for CABMV were obtained from western Kenya. Bayesian phylogenomic analysis and tests for differential selection pressure within sites and across tree branches of the viral genomes were carried out. Three well–supported clades in BCMNV and one supported clade for CABMNV were resolved and in agreement with individual gene trees. Selection pressure analysis within sites and across phylogenetic branches suggested both viruses were evolving independently, but under strong purifying selection, with a slow evolutionary rate. These findings provide valuable insights on the evolution of BCMNV and CABMV genomes and their relationship to other viral genomes globally. The results will contribute greatly to the knowledge gap involving the phylogenomic relationship of these viruses, particularly for CABMV, for which there are few genome sequences available, and inform the current breeding efforts towards resistance for BCMNV and CABMV.

Risk factors for Plasmodium falciparum infection in the Kenyan Highlands: a cohort study.

BackgroundMalaria transmission in African highland areas can be prone to epidemics, with minor fluctuations in temperature or altitude resulting in highly heterogeneous transmission. In the Kenyan Highlands, where malaria prevalence has been increasing, characterising malaria incidence and identifying risk factors for infection is complicated by asymptomatic infection.MethodsThis all-age cohort study, one element of the Malaria Transmission Consortium, involved monthly follow-up of 3155 residents of the Kisii and Rachuonyo South districts during June 2009–June 2010. Participants were tested for malaria using rapid diagnostic testing at every visit, regardless of symptoms.ResultsThe incidence of Plasmodium falciparum infection was 0.2 cases per person, although infections were clustered within individuals and over time, with the majority of infections detected in the last month of the cohort study. Overall, incidence was higher in the Rachuonyo district and infections were detected most frequently in 5–10-year-olds. The majority of infections were asymptomatic (58%). Travel away from the study area was a notable risk factor for infection.ConclusionsIdentifying risk factors for malaria infection can help to guide targeting of interventions to populations most likely to be exposed to malaria.

Microbial biomass and acid phosphomonoesterase activity in soils of the Central Highlands of Kenya

Soil biological properties are the most sensitive soil quality indicators that respond quickly to short-term soil fertility management changes. We studied the combined effects of tillage and soil external inputs on total soil organic carbon and nitrogen, microbial biomass carbon (MBC) and nitrogen (MBN) and acid phosphomonoesterase activity (ACP). This was done in Meru South and Kandara sub-counties in Kenya for three consecutive cropping seasons. Tillage was the main factor [minimum (D0) and conventional (D15)], and soil external inputs were the sub-factors: sole mineral fertiliser (F), crop residues + mineral fertiliser (RF), crop residues + animal manure + legume intercrop Dolichos lablab L. (RML), crop residues + mineral fertiliser + animal manure (RFM), crop residues + Tithonia diversifolia + animal manure (RTiM), crop residues + Tithonia diversifolia + rock phosphate (RTiP) and an unfertilized treatment (Control). During the study period, we experienced frequent dry spells and meteorological droughts in the two sites. We found no significant effects of the tillage systems and mineral fertilisers applied alone or combined with crop residues on the biological properties. All additional organic inputs to the soils enhanced the biological soil properties. On average, MBC in the treatments with organic inputs only was enhanced by 51% in Meru South and 19% in Kandara. MBC-to-TOC ratio was significantly different (p = .0003) under soil external inputs in Meru South. On average, MBN in the treatments with organic inputs was enhanced by 66% in Meru South and 25% in Kandara. Compared with the control, ACP was higher under RML, RTiP and RTiM by 26%, 20% and 17%, respectively in Meru South. In Kandara, ACP was higher under RTiM and RTiP by 25% and 23%, respectively, compared with the control. The increase in microbial biomass indicates that application of organic inputs contributed to soil organic C, thereby stimulating the microbial growth and enzyme activity. Thus, use of organic inputs or in combination with mineral fertilisers are feasible alternatives for sustaining soil organic carbon through increased microbial biomass leading to soil organic matter build-up, which is a vital element of soil quality and fertility.

DNA Analysis of Ralstonia solanacearum Based on 270-bp PCR-amplified Fragment from the Lowlands and Highlands of Kenya

DNA Analysis of Ralstonia solanacearum Based on 270-bp PCR-amplified Fragment from the Lowlands and Highlands of Kenya

Uncertainty in malaria simulations in the highlands of Kenya: Relative contributions of model parameter setting, driving climate and initial condition errors.

In this study, experiments are conducted to gauge the relative importance of model, initial condition, and driving climate uncertainty for simulations of malaria transmission at a highland plantation in Kericho, Kenya. A genetic algorithm calibrates each of these three factors within their assessed prior uncertainty in turn to see which allows the best fit to a timeseries of confirmed cases. It is shown that for high altitude locations close to the threshold for transmission, the spatial representativeness uncertainty for climate, in particular temperature, dominates the uncertainty due to model parameter settings. Initial condition uncertainty plays little role after the first two years, and is thus important in the early warning system context, but negligible for decadal and climate change investigations. Thus, while reducing uncertainty in the model parameters would improve the quality of the simulations, the uncertainty in the temperature driving data is critical. It is emphasized that this result is a function of the mean climate of the location itself, and it is shown that model uncertainty would be relatively more important at warmer, lower altitude locations.

English

Effective promotion of artificial insemination (AI) by private providers in pastoral areas requires stakeholders’ opinion in shaping the direction of their adoption. A structured questionnaire was administered to 384 pastoralists in Kajiado and Narok counties, Kenya to elicit data on willingness to pay for AI services. Double bounded contingent valuation methodology was adapted in computing their willingness to pay for AI services. Results revealed that 90% of farmers were aware of AI of which 51.7 and 50.5% were willing to pay for the services in Kajiado and Narok counties respectively, for an average of Kenya Shillings 1, 853, reflecting a premium of 23.6% placed on AI by pastoralists with reference to the base price of Kenya Shillings (KES) 1,500 offered for exotic breeds in Kenyan highlands. Awareness, herd size and access to extension services significantly increase farmers’ willingness to pay unlike farm income. The study recommends utilization of existing extension networks of community animal health workers to ensure relevant information about AI is disseminated among pastoralists and perform free AI trials on lead pastoralists’ animals to earn others’ confidence. Key words: Artificial insemination, willingness to pay, pastoralists, adoption, contingency valuation, awareness, Maasai.

EFFECTS OF BLENDED FERTILIZERS ON YIELDS OF MATURE TEA CLONES TRFK 6/8 AND BBK 35 GROWN IN KENYAN HIGHLANDS

&lt;p&gt;Kenya’s tea industry depends predominantly on imported NPK fertilizers to replenish nutrients removed through plucking. In this respect, two blended fertilizers containing NPKS 25:5:5:4+9Ca+2.6Mg and NPKS 23:5:5:4+10Ca+3Mg with trace elements have been produced in the country. However, contribution of the blended fertilizers to optimal tea yields had not been determined. The study aimed to evaluate the optimal levels of the two blended fertilizers on tea grown in the highlands of Kenya. The blended fertilizers were evaluated in two sites, i.e. Timbilil estate in Kericho and Kagochi farm in Nyeri. The trial was laid out in a randomized complete block design with two blended fertilizers and the standard NPK 26:5:5 as a control. The treatments were applied at four fertilizer rates (0-control, 75, 150 and 225 kg N ha-1 yr-1), with three replications. The results showed that application of 225 kg N ha-1 yr-1 blended fertilizer NPKS 25:5:5:4+9Ca+2.6Mg in Timbilil produced mean yield of 2,995 kg Mt ha-1 compared with 3,099 kg Mt ha-1 from the standard NPK. In Kagochi, the highest yield was 1,975 kg Mt ha-1 obtained from the application of the same blended fertilizer NPKS 25:5:5:4+9Ca+2.6Mg at 75 kg N ha-1 yr-1. The highest yields in both sites were obtained during a warm-dry season except in 2015-2016. This study concluded that based on the annual and seasonal yields, the two blended fertilizers and the standard type had the same effectiveness, irrespective of clones and sites. However, the fertilizer rates affected the tea yield.&lt;/p&gt;

Genomic characterisation and evolutionary relationships of groundnut rosette virus from the western highlands of Kenya

Viral symptomatic groundnut (Arachis hypogaea L.) leaf samples were collected in the heterogeneous agro-ecosystem of the western highlands of Kenya. High throughput RNA sequencing (RNA-Seq) was carried out on total plant RNA using the Illumina HiSeq platform. Subsequently, de novo assembly and sequence similarity searches identified the complete genome of Groundnut rosette virus (GRV). The genome consisted of 4298 nucleotides, encoding three open reading frames (ORF1-ORF3) including an RNA-dependent RNA polymerase gene. A sequence similarity search against GenBank reference sequences matched with 84% identity to a Malawian isolate (Z69910). Bayesian evolutionary relationships using the ORF3 and ORF4 genomic regions clustered the Kenyan isolates within a distinct clade. This study provides the first complete genome of GRV from Kenya and provides a genomic resource for the development of molecular diagnostic tools.

Efficacy and persistence of long-lasting microbial larvicides against malaria vectors in western Kenya highlands

BackgroundChemical-based malaria vector control interventions are threatened by the development of insecticide resistance and changes in the behavior of the vectors, and thus require the development of alternative control methods. Bacterial-based larvicides have the potential to target both insecticide resistant and outdoor-biting mosquitoes and are safe to use in the environment. However, the currently available microbial larvicide formulations have a short duration of activity requiring frequent re-applications which increase the cost of control interventions. This study was designed to evaluate the efficacy and duration of activity of two long-lasting formulations of Bacillus thuringiensis var. israelensis (Bti) and Bacillus sphaericus (Bs) (LL3 and FourStar®) under field conditions in western Kenya highlands.MethodsThree sites were selected for this study in the highlands of western Kenya. In each site, one hundred anopheline larval habitats were selected and assigned to one of three arms: (i) LL3; (ii) FourStar®; and (iii) untreated control larval habitats. Four types of larval habitats were surveyed: abandoned gold mines, drainage canals, fish ponds and non-fish ponds. The habitats were sampled for mosquito larvae by using a standard dipping technique and collected larvae were recorded according to the larval stages of the different Anopheles species. The larvicides were applied at manufacturers’ recommended dosage of 1 briquette per 100 square feet. Both treatment and control habitats were sampled for mosquito larvae immediately before treatment (day 0), and then at 24 hours, 3 days and weekly post-treatment for 5 months.ResultsOverall larval density in treatment habitats was significantly reduced after application of the two microbial larvicides as compared to the control habitats. Post-intervention reduction in anopheline larval density by LL3 was 65, 71 and 84% for 1 day, 2 weeks and 4 weeks, respectively. FourStar® reduced anopheline larval density by 60, 66 and 80% for 1 day, 2 weeks and 4 weeks, respectively. Comparisons between the treatments reveal that LL3 and FourStar® were similar in efficacy. A higher reduction in Anopheles larval density was observed in the abandoned goldmines, while drainage canals had the lowest reduction.ConclusionsBoth LL3 and FourStar® long-lasting microbial larvicides were effective in reducing immature stages of An. gambiae complex and An. funestus group species, with significant reductions lasting for three months post-application.

Phylogenomic relationship and evolutionary insights of sweet potato viruses from the western highlands of Kenya.

Sweet potato is a major food security crop within sub-Saharan Africa where 90% of Africa production occurs. One of the major limitations of sweet potato production are viral infections. In this study, we used a combination of whole genome sequences from a field isolate obtained from Kenya and those available in GenBank. Sequences of four sweet potato viruses: Sweet potato feathery mottle virus (SPFMV), Sweet potato virus C (SPVC), Sweet potato chlorotic stunt virus (SPCSV), Sweet potato chlorotic fleck virus (SPCFV) were obtained from the Kenyan sample. SPFMV sequences both from this study and from GenBank were found to be recombinant. Recombination breakpoints were found within the Nla-Pro, coat protein and P1 genes. The SPCSV, SPVC, and SPCFV viruses from this study were non-recombinant. Bayesian phylogenomic relationships across whole genome trees showed variation in the number of well-supported clades; within SPCSV (RNA1 and RNA2) and SPFMV two well-supported clades (I and II) were resolved. The SPCFV tree resolved three well-supported clades (I–III) while four well-supported clades were resolved in SPVC (I–IV). Similar clades were resolved within the coalescent species trees. However, there were disagreements between the clades resolved in the gene trees compared to those from the whole genome tree and coalescent species trees. However the coat protein gene tree of SPCSV and SPCFV resolved similar clades to the genome and coalescent species tree while this was not the case in SPFMV and SPVC. In addition, we report variation in selective pressure within sites of individual genes across all four viruses; overall all viruses were under purifying selection. We report the first complete genomes of SPFMV, SPVC, SPCFV, and a partial SPCSV from Kenya as a mixed infection in one sample. Our findings provide a snap shot on the evolutionary relationship of sweet potato viruses (SPFMV, SPVC, SPCFV, and SPCSV) from Kenya as well as assessing whether selection pressure has an effect on their evolution.