Papers by Johnson Nyasani
Potential of using entomopathogenic nematodes in the management of diamondback moth Plutella xylostella (L.) (Lepidoptera: Plutellidae) in Kenya
8th African Crop Science Society Conference, El-Minia, Egypt, 27-31 October 2007, 2007
... JO NYASANI1, JW KIMENJU1, FM OLUBAYO1 & MJ WILSON2 1Department of Plant Science and Crop ... more ... JO NYASANI1, JW KIMENJU1, FM OLUBAYO1 & MJ WILSON2 1Department of Plant Science and Crop Protection, University of Nairobi, Kenya PO Box 30197 ... translates to US$ 7.9 million per year for the whole country and control costs amount to US$ 118.9/ha (Macharia et al ...
Prospects of Classical Biological Control of Papaya Mealybug in Kenya: Performance of its Exotic Parasitoid, Acerophagus Papayae, Under Laboratory and Field Conditions
Estimating maize lethal necrosis (MLN) severity in Kenya using multispectral high-resolution data
Applied Geomatics
Maize lethal necrosis (MLN) is a severe disease in maize that significantly reduces yields by up ... more Maize lethal necrosis (MLN) is a severe disease in maize that significantly reduces yields by up to 90% in maize-growing regions such as Kenya and other countries in Africa. The disease causes chlorotic mottling of leaves and severe stunting which leads to plant death. The spread of MLN in the maize-growing regions of Kenya has intensified since the first outbreak was reported in September 2011. In this study, the RapidEye (5 m) imagery was combined with field-based data of MLN severity to map three MLN severity levels in Bomet County, Kenya. Two RapidEye images were acquired during maize stem elongation and inflorescence stages, respectively, and thirty spectral indices for each RapidEye time step were computed. A two-step random forest (RF) classification algorithm was used to firstly create a maize field mask and to predict the MLN severity levels (mild, moderate, and high). The RF algorithm yielded an overall accuracy of 91.0%, representing high model performance in predicting the MLN severity levels in a complex cropping system. The normalized difference red edge index (NDRE) was highly sensitive to MLN detection and demonstrated the ability to detect MLN-caused crop stress earlier than the normalized difference vegetation index (NDVI) and the green normalized difference vegetation index (GNDVI). These results confirm the potential of the RapidEye sensor and machine learning to detect crop disease infestation rates and for use in MLN monitoring in fragmented agro-ecological landscapes.
Land use effects on termite assemblages in Kenya
Heliyon, 2021
Termites perform key ecological functions and they also cause crop damage. Land use change result... more Termites perform key ecological functions and they also cause crop damage. Land use change resulting from agricultural intensification can result in changes in termite species diversity and abundance. Termite species occurring in natural vegetation, maize monocrop and maize-beans intercrop macrohabitats were investigated in Embu and Machakos Counties, Kenya. Influence of soil properties and seasons was also evaluated. Across the two Counties, seven termite species were recorded with Machakos County having the highest number. Additive diversity partitioning of species richness and Simpson diversity showed that, α component contributed to 98.3% and 99.1% of the total diversity, respectively. Population densities of three termite species significantly varied between land use types in Machakos County but there were no differences in termite species abundance in Embu County. In addition, there were no significant differences in species richness between macrohabitats within each County. In Embu, season significantly influenced the abundance of Macrotermes subhyalinus, M. herus, and Coptotermes formosanus which occurred in greater numbers during the wet season. There was a significant influence of land use on Trinervitermes gratiosus and C. formosanus in Machakos with both species occurring in higher numbers in natural vegetation. Trinervitermes gratiosus was negatively associated with Mn and positively correlated to pH and sand. Macrotermes subhyalinus and M. herus showed a positive association with P and silt while C. formosanus was positively correlated to Ca and Mg. These findings provide an insight into the effects of land use change from natural vegetation to maize agro-ecosystems on termite diversity. It also provides a baseline for further studies on termite diversity in Kenya and their ecological significance.
Establishment of an Exotic Parasitoid Cotesia vestalis in Coastal Areas of Kenya as Biological Control Agent of Plutella xylostella
The aims of this study were to follow up on the establishment of Cotesia vestalis in the coastal ... more The aims of this study were to follow up on the establishment of Cotesia vestalis in the coastal regions of Kenya, assessing its contribution in the management of the diamondback moth (Plutella xylostella), parasitism rates, and cultural practices affecting its establishment. Post-release surveys were carried out in five counties in Kenya, Kitui, Kajiado, Kwale, Machakos and Makueni, between 2015 and 2016. The results showed that the overall parasitism rate of C. vestalis in 2015 ranged between 0% and 37.86% while that in 2016 ranged from 0% to 32.19% in the different counties. Farmers carry out routine sprays, either weekly or fortnightly, with different synthetic insecticides. Pyrethroids (60.56%) constituted most of the insecticides used, while only 3.18% of the products used were plant or microorganism- based. Farmers did most of their cabbage production during the rainy season, with production being greatly reduced during the dry seasons. The sampled diamondback moths from Kaji...
Prospects of Fungus-Based Biopesticides for Management of Insect Vectors of Maize Lethal Necrosis Disease
Maize, Zea mays L., production in Kenya is constrained by both biotic and abiotic factors. For in... more Maize, Zea mays L., production in Kenya is constrained by both biotic and abiotic factors. For instance, maize lethal necrosis (MLN) was first reported in Bomet County in 2011 and has since spread to other maize growing areas. In Kenya, MLN is reported to be caused by a co-infection of maize plant by Maize chlorotic mottle virus (MCMV) and Sugarcane mosaic virus (SCMV). Since this disease is new to Africa, there is little information about management of its insect vectors. To develop management strategies for MLN insect vectors, a field experiment was conducted using fungus-based biopesticides, Metarhizium anisopliae (MA) and Trichoderma asperellum (TA), and Nurelle*D 50/500EC (NuD) insecticide. Seven treatment were used: 1) untreated plot; 2) soil application of TA with foliar sprays of NuD; 3) soil application of TA with foliar spray of MA; 4) soil application of TA with foliar spray of MA and NuD; 5) foliar spray of NuD alone; 6) foliar sprays of MA alone; 7) soil application of ...
Termite species and functional groups in maize intercrop systems in Machakos County, Kenya
Crop Protection, 2022
Attraction of pest thrips (Thysanoptera: Thripidae) infesting French beans to coloured sticky traps with Lurem-TR and its utility for monitoring thrips populations
International Journal of Tropical Insect Science, 2014
In the present study, experiments were carried out in French bean fields over two planting period... more In the present study, experiments were carried out in French bean fields over two planting periods to evaluate the potential use of sticky traps for monitoring the populations of pest thrips. To this end, blue, yellow and clear sticky traps (with and without a thrips lure, i.e. Lurem-TR) were tested. Field observations on thrips catches were made at weekly intervals from the sticky traps, and absolute estimates of thrips populations and their natural enemies were made by destructive (picking leaves and flowers) and non-destructive sampling (plant tapping) of plants until crop senescence during the two planting periods. Blue traps caught two and three times more thrips compared with yellow traps over the first and second planting periods, respectively. Blue traps were more attractive to Megalurothrips sjostedti (Trybom), Frankliniella schultzei (Trybom) and Frankliniella occidentalis (Pergande), while yellow traps were only attractive to Hydatothrips adolfifriderici (Karny) and the n...
Invasive alien species (IAS) rank among the most significant drivers of species extinction and ec... more Invasive alien species (IAS) rank among the most significant drivers of species extinction and ecosystem degradation, causing significant impacts on ecosystem services, human well-being and socio-economic development. Recent invasions have spread rapidly in Africa due to porous borders constraining maintenance of border biosecurity. Countries also lack adequate information about potential invasions and have limited capacity to reduce risk of invasions. Horizon scanning prioritises the risks of potential IAS through rapid assessments of likelihood of their entry and establishment and their potential socio-economic and environmental impacts. This approach was used to identify and assess risks of 120 potential IAS (70 arthropods, 41 pathogens and 9 nematodes) to Kenya. The likely pathway of arrival for assessed species was mainly as contaminants of commodities, but some could most likely enter as stowaways. All species were scored for likelihood of entry, likelihood of establishment, p...
Genome Biology and Evolution, 2020
Busseola fusca (Fuller) (Lepidoptera: Noctuidae), the maize stalk borer, is a widespread crop pes... more Busseola fusca (Fuller) (Lepidoptera: Noctuidae), the maize stalk borer, is a widespread crop pest in sub-Saharan Africa that has been the focus of biological research and intensive management strategies. Here, we present a comprehensive annotated transcriptome of B. fusca (originally collected in the Western Province of Kenya) based on ten pooled libraries including a wide array of developmental stages, tissue types, and exposures to parasitoid wasps. Parasitoid wasps have been used as a form of biocontrol to try and reduce crop losses with variable success, in part due to differential infectivities and immune responses among wasps and hosts. We identified a number of loci of interest for pest management, including genes potentially involved in chemoreception, immunity, and response to insecticides. The comprehensive sampling design used expands our current understanding of the transcriptome of this species and deepens the list of potential target genes for future crop loss mitigat...
Plants, 2020
In eastern Africa, Maize lethal necrosis (MLN) is caused by the co-infection of maize plants with... more In eastern Africa, Maize lethal necrosis (MLN) is caused by the co-infection of maize plants with Maize chlorotic mottle virus (MCMV) (Tombusviridae: Machlomovirus) and Sugarcane mosaic virus (SCMV) (Potyviridae: Potyvirus). With the disease being new to Africa, minimal effective management strategies exist against it. This study examined the potential of 10 fungal isolates to colonize maize plants and induce resistance against MCMV and SCMV. Maize seeds were soaked in fungal inoculum, sown and evaluated for endophytic colonization. Fungus-treated plants were challenge-inoculated with SCMV and/or MCMV to assess the effects of fungal isolates on the viruses in terms of incidence, severity and virus titers over time. Isolates of Trichoderma harzianum, Trichoderma atroviride and Hypocrea lixii colonized different plant sections. All plants singly or dually-inoculated with SCMV and MCMV tested positive for the viruses by reverse transcription-polymerase chain reaction (RT-PCR). Maize pl...
Thrips as vectors of an emerging maize disease: A case study of maize chlorotic mottle virus
2016 International Congress of Entomology, 2016
Journal of chemical ecology, 2018
Maize lethal necrosis is one of the most devastating diseases of maize causing yield losses reach... more Maize lethal necrosis is one of the most devastating diseases of maize causing yield losses reaching up to 90% in sub-Saharan Africa. The disease is caused by a combination of maize chlorotic mottle virus (MCMV) and any one of cereal viruses in the Potyviridae group such as sugarcane mosaic virus. MCMV has been reported to be transmitted mainly by maize thrips (Frankliniella williamsi) and onion thrips (Thrips tabaci). To better understand the role of thrips vectors in the epidemiology of the disease, we investigated behavioral responses of F. williamsi and T. tabaci, to volatiles collected from maize seedlings infected with MCMV in a four-arm olfactometer bioassay. Volatile profiles from MCMV-infected and healthy maize plants were compared by gas chromatography (GC) and GC coupled mass spectrometry analyses. In the bioassays, both sexes of F. williamsi and male T. tabaci were significantly attracted to volatiles from maize plants infected with MCMV compared to healthy plants and so...
Sensors (Basel, Switzerland), Jan 3, 2017
Cropping systems information on explicit scales is an important but rarely available variable in ... more Cropping systems information on explicit scales is an important but rarely available variable in many crops modeling routines and of utmost importance for understanding pests and disease propagation mechanisms in agro-ecological landscapes. In this study, high spatial and temporal resolution RapidEye bio-temporal data were utilized within a novel 2-step hierarchical random forest (RF) classification approach to map areas of mono- and mixed maize cropping systems. A small-scale maize farming site in Machakos County, Kenya was used as a study site. Within the study site, field data was collected during the satellite acquisition period on general land use/land cover (LULC) and the two cropping systems. Firstly, non-cropland areas were masked out from other land use/land cover using the LULC mapping result. Subsequently an optimized RF model was applied to the cropland layer to map the two cropping systems (2nd classification step). An overall accuracy of 93% was attained for the LULC c...
International Journal of Tropical Insect Science, 2017
The short-range diurnal dispersal pattern of adult western flower thripsFrankliniella occidentali... more The short-range diurnal dispersal pattern of adult western flower thripsFrankliniella occidentalis(Pergande), in relation to spatial distribution of French beans, was determined in the field. A total of 1200 adult femaleF. occidentaliswere released on 60 French bean plants with 20 adult thrips per plant at the central release point of 3.14 m2. Dispersal was determined in terms of the number of thrips recorded on French beans planted on concentric circles at 0.9, 1.8, 3.6, 7.2 and 14.4 m radii from a circular central release point for five days. Results indicated that there was a steady increase in the proportion of dispersing adultF. occidentalisfrom the first to the fourth day in the first planting season, and from the first to the third day in the second planting season. The peak hour for dispersal was 10.15 h in the first season while it was 13.15 h in the second season. Temperature and wind speed were positively associated with the dispersal activity of adultF. occidentalis. Min...
Diversity, distribution and plant association of thrips belonging to Frankliniella genus in East Africa
The genus Frankliniella Karny is the second largest in the family Thripidae with many polyphagous... more The genus Frankliniella Karny is the second largest in the family Thripidae with many polyphagous thrips and tospovirus vectors which are Neotropic and Nearctic in origin. The invasive Western Flower Thrips (WFT), Frankliniella occidentalis (Pergande) and F. schultzei Trybom are known to occur in East Africa. However detailed information on the distribution and diversity of Frankliniella sp. is lacking in East Africa. Detailed surveys in over 250 locations were undertaken from August 2008 to July 2010. Both the dark and pale forms of WFT were found restricted to the high and mid altitude regions of Kenya. Frankliniella schultzei, the most widespread species was observed in high-, mid- and low altitude regions of East Africa. Both pale forms with short third ocellar setae (OSIII) and dark forms with long OSIII were observed in East Africa. Molecular analysis of the ITS1/ITS2 sequences of F. schultzei forms with RFLP technique indicated high degree of divergence between them. While WF...
Role of vectors and their host plants in the epidemiology of maize lethal necrosis in eastern Africa
The prevalence and severity of a new maize disease complex known as Maize Lethal Necrosis (MLN) c... more The prevalence and severity of a new maize disease complex known as Maize Lethal Necrosis (MLN) caused by viruses such as Maize chlorotic mottle virus (MCMV), and Sugarcane mosaic virus (SCMV) has resulted in 100% yield loss in severely affected areas in Kenya. The disease has spread rapidly to other eastern Africa countries like Uganda, Tanzania, Rwanda and DRC Congo. Despite this rapid spread, role of potential vectors in the disease epidemiology and sustainable vector management strategies are poorly understood in eastern Africa. Hence we focused to identify potential vectors and estimate their competencies to transmit MLN-causing viruses, and to determine their host plants and natural enemies. Field surveys to determine the seasonality and diversity of potential vectors of MLN-casing viruses were carried out in MLN hotspots in Kenya. The presence of MLN viruses in wild grasses and other cereal crops were detected by DAS-ELISA and RT-PCR. Potential vectors in the MLN positive hos...
Feeding and oviposition preference of
Western flower thrips (WFT), Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), is ... more Western flower thrips (WFT), Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), is an important pest of French beans in Kenya. However, information on the feeding activity and oviposition preference of WFT on crop and weed hosts associated with French beans in Kenya and other parts of the world is lacking. To determine the feeding and oviposition preference of WFT for crop and weed plants commonly encountered in French bean fields in Kenya, no-choice and choice experiments were conducted using four important crop and weed plants. Among the crop plants tested, highest feeding and oviposition activity of WFT was recorded on courgette/zucchini (Cucurbita pepo L.) and French beans (Phaseolus vulgaris L.). Spinach beet (Beta vulgaris L.) and sweet pepper (Capsicum annuum L.) were of relatively minor importance for feeding and oviposition. Among the weeds tested, gallant soldier (Galinsoga parviflora Cav.) was the most preferred host plant for feeding and oviposition compare...
Insects, 2015
Western flower thrips (WFT), Frankliniella occidentalis (Pergande), is an important pest of veget... more Western flower thrips (WFT), Frankliniella occidentalis (Pergande), is an important pest of vegetable crops worldwide and has developed resistance to many insecticides. The predatory mites Neoseiulus (=Amblyseius) cucumeris (Oudemans), the entomopathogenic fungus Metarhizium anisopliae (Metsch.), and an insecticide (imidacloprid) were tested for their efficacy to reduce WFT population density and damage to French bean (Phaseolus vulgaris L.) pods under field conditions in two planting periods. Metarhizium anisopliae was applied as a foliar spray weekly at a rate of one litre spray volume per plot while imidacloprid was applied as a soil drench every two weeks at a rate of two litres of a mixture of water and imidacloprid per m 2 . Neoseiulus cucumeris was released every two weeks on plant foliage at a rate of three mites per plant. Single and combined treatment applications reduced WFT population density by at least three times and WFT damage to French bean pods by at least 1.7 times compared with untreated plots. The benefit-cost ratios in management of WFT OPEN ACCESS Insects 2015, 6 280 were profitable with highest returns realized on imidacloprid treated plots. The results indicate that M. anisopliae, N. cucumeris, and imidacloprid have the potential for use in developing an integrated pest management program against WFT on French beans.
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Papers by Johnson Nyasani