Browsing by Author "Belmain, Steven"

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Beneficial insects are associated with botanically rich margins with trees on small farms
(2021-07-21) Arnold, Sarah; Elisante, Filemon; Mkenda, Prisila; Tembo, Yolice; Ndakidemi, Patrick; Gurr, Geoff; Darbyshire, Iain; Belmain, Steven; Stevenson, Philip
Beneficial insect communities on farms are influenced by site- and landscape-level factors, with pollinator and natural enemy populations often associated with semi-natural habitat remnants. They provide ecosystem services essential for all agroecosystems. For smallholders, natural pest regulation may be the only affordable and available option to manage pests. We evaluated the beneficial insect community on smallholder bean farms (Phaseolus vulgaris L.) and its relationship with the plant communities in field margins, including margin trees that are not associated with forest fragments. Using traps, botanical surveys and transect walks, we analysed the relationship between the floral diversity/composition of naturally regenerating field margins, and the beneficial insect abundance/diversity on smallholder farms, and the relationship with crop yield. More flower visits by potential pollinators and increased natural enemy abundance measures in fields with higher plant, and particularly tree, species richness, and these fields also saw improved crop yields. Many of the flower visitors to beans and potential natural enemy guilds also made use of non-crop plants, including pesticidal and medicinal plant species. Selective encouragement of plants delivering multiple benefits to farms can contribute to an ecological intensification approach. However, caution must be employed, as many plants in these systems are introduced species.
Biopesticides Potential to Protect Tomato (Solanum lycopersicum L.) Production from Early Blight Disease (Alternaria solani) and Leaf Miners (Tuta absoluta)
(preprint, 2025-01-03) Abel, Fikiri; Mkindi, Angela; Mbega, Ernest; Stevenson, Philip; Belmain, Steven; Venkataramana, Pavithravani
Early blight disease (Alternaria solani) and leaf miners (Tuta absoluta) pose significant biotic constraints to tomato production, causing 80 -100% yield loss. A study involving laboratory, screen house and field experiments evaluated the efficacy of plant and bio product pesticides including extracts of Azadirachta indica, Lantana camara , Cymbopogon citratus, Capsicum frutescens, Zingiber officinal and rabbit urine. We report significant inhibition of fungal mycelial growth ranging from 20% with a 5% rabbit urine to 98.25% by 10% hot pepper in the laboratory. Screen house trials showed a positive inhibitory effect of plant extracts on controlling leaf miners. The most effective extracts were 10% lantana (80%), 10% hot pepper (76.6%) and 10% ginger (72.6%).The most successful four extracts were used in field trials and resulted in an average 50% reduction in disease severity compared to the control. Also, 10% ginger, hot pepper (both 5% and 10%) and 10% lantana were effective in controlling Tuta absoluta and significantly reduced leaf damage. A cost benefit analysis showed that the 5% hot pepper treatment had the highest revenue benefit compared to the negative control and conventional tomato production methods. Further research is needed to integrate these biopesticides into crop management practices.
Botanical extracts control the fungal pathogen Colletotrichum boninense in smallholder production of common bean
(Springer link, 2024-04-11) Kushaha, Tamia; Mkindi, Angela; Mbega, Ernest; Stevenson, Philip; Belmain, Steven
Anthracnose caused by Colletotrichum spp. remains an intractable problem in the most common bean (Phaseolus vulgaris) production areas worldwide and can cause total yield loss. Many smallholder farmers are familiar with using botanical extracts to control insect pests; however, there is less familiarity with their use to control fungal diseases due to a lack of evidence. Here, we demonstrate that anthracnose could be controlled effectively by pesticidal plant species that are used for insect control. In laboratory trials, water extracts from 11 plant species could inhibit fungal growth (100%) and spore germination (75–100%) equally well to two commercially available fungicides, the syn- thetic Mancolaxyl and biofungicide Bioderma. In screenhouse trials, anthracnose disease was reduced by the extracts of three plant species. Moreover, bean crop growth in these botanical treatments did not differ significantly from that observed in the commercial fungicide treated plants. Field trials in a smallholder community reporting severe problems with anthracnose showed an effect similar to the screenhouse results. Field trials resulted in bean seed yields approximately 350 kg/ha higher in bean plants treated with Azadirachta indica and Lippia javanica at 10% w/v compared to the negative control untreated plants. In all trials, botanical extracts were as effective as commer- cially available fungicides, suggesting that these botanical extracts could provide dual-purpose pest and disease management for anthracnose and crop pest insects. The outcomes of this research show that prospects for using locally available resources to control anthracnose on common bean are credible and can be combined with control- ling insect pests.
The diversity of aphid parasitoids in East Africa and implications for biological control
(Wiley Online Library, 2021-11-18) Woolley, Victoria; Tembo, Yolice; Ndakidemi, Baltazar; Obanyi, Janet; Arnold, Sarah; Belmain, Steven; Ndakidemi, Patrick; Ogendo, Joshua; Stevenson, Philip
BACKGROUND Hymenopteran parasitoids provide key natural pest regulation services and are reared commercially as biological control agents. Therefore, understanding parasitoid community composition in natural populations is important to enable better management for optimized natural pest regulation. We carried out a field study to understand the parasitoid community associated with Aphis fabae on East African smallholder farms. Either common bean (Phaseolus vulgaris) or lablab (Lablab purpureus) sentinel plants were infested with Aphis fabae and deployed in 96 fields across Kenya, Tanzania, and Malawi. RESULTS A total of 463 parasitoids emerged from sentinel plants of which 424 were identified by mitochondrial cytochrome oxidase I (COI) barcoding. Aphidius colemani was abundant in Kenya, Tanzania and Malawi, while Lysiphlebus testaceipes was only present in Malawi. The identity of Aphidius colemani specimens were confirmed by sequencing LWRh and 16S genes and was selected for further genetic and population analyses. A total of 12 Aphidius colemani haplotypes were identified. Of these, nine were from our East African specimens and three from the Barcode of Life Database (BOLD). CONCLUSION Aphidius colemani and Lysiphlebus testaceipes are potential targets for conservation biological control in tropical smallholder agro-ecosystems. We hypothesize that high genetic diversity in East African populations of Aphidius colemani suggests that this species originated in East Africa and has spread globally due to its use as a biological control agent. These East African populations could have potential for use as strains in commercial biological control or to improve existing Aphidius colemani strains by selective breeding.
Elements of agroecological pest and disease management
(University of California Press, 2022-06-01) Belmain, Steven; Tembo, Yolice; Mkindi, Angela; Arnold, Sarah; Stevenson, Philip
The development of large-scale monocropped agrisystems has facilitated increased problems with pests and diseases, perpetuating the reliance of farmers on synthetic pesticides. The economic success of synthetic inputs has, however, been achieved at a high cost to the environment through the loss of biodiversity, depletion of soil quality, greenhouse gas emissions, and disrupting the ecosystem services that can otherwise help mitigate losses caused by pests and diseases. Environmentally benign alternatives for pest and disease management are urgently needed and are now widely recognized as essential for sustainable food and agriculture. The Food and Agriculture Organization, for example, has published the 10 elements of agroecology as a framework for the transformation of agriculture. Agroecology combines ecological and social concepts and principles to develop sustainable food and agricultural systems by harnessing nature based solutions that are tailored to farmers’ needs. Plant-based biopesticides, for example, offer an alternative to synthetic pesticides that are less harmful to the environment and nonpersistent, yet effective at managing pests and have a long tradition of use among farmers so are more socially acceptable. Here, we provide a critical assessment of how nature-based approaches to pest and disease management comply with the 10 elements of agroecology and show how they integrate with other ecosystem services through farmer participatory research. We conclude that the adoption of nature-based solutions for pest management addresses all 10 elements of agroecology and provides an entry point to promote sustainable farming practices among farmers more widely.
Enhancing knowledge among smallholders on pollinators and supporting field margins for sustainable food security
(Elsevier Ltd., 2019-08) Elisante, Filemon; Ndakidemi, Patrick; Arnold, Sarah; Belmain, Steven; Gurr, Geoff; Darbyshire, Iain; Xie, Gang; Tumbo, Julie; Stevenson, Philip
Agro-ecological intensification (AEI) harnesses natural processes, such as pollination, that support sustainable crop production and can buffer against future food security risks. However, the transition from conventional agriculture, which relies on inputs that can damage natural ecosystem processes, to more sustainable food production under AEI, is knowledge-intensive. Here, we investigated knowledge gaps among smallholder farmers about pollinators and field margins in a bean agri-system in Tanzania. While 77% of farmers were familiar with and identified honeybees correctly prior to training, only 52% understood their role as a pollinator of crops. Furthermore, 80% and 98% of farmers were unaware of the significance of wild (solitary) bees or the importance of hoverflies as pollinators. A high level of synthetic agrochemical use was reported for the management of pests and weeds, particularly in the more agriculturally intensive production systems. However, an end-line survey conducted one year after training showed an increase in knowledge and the majority of farmers, 99%, 54% and 62% subsequently recognised honeybees, hoverflies and solitary bees respectively, by name. Furthermore, 95%, 69% and 60% of farmers understood the importance of honeybees, hoverflies and solitary bees respectively, as crop pollinators and natural enemies (for hoverflies). Similarly, a majority of farmers recognised the benefits of biopesticides as environmentally safer over synthetic pesticides as well as the value of field margins in supporting pollinators and other ecosystem services. We argue that, improving understanding among smallholder farmers of ecosystem services and their ecological requirements is both feasible and essential to achieving sustainable intensification in small holder farming systems.
Enhancing sustainable agriculture through farmer research networks: a pathway to co-learning and innovation
(University of Greenwich, 2025-05-01) Stevenson, Philip; Mkindi, Angela; Tembo, Yolice; Belmain, Steven
Smallholder farming communities face numerous challenges in securing food production sustainably, often stemming from poor levels of adoption, or uptake, of researcher-led interventions and innovations. Farmer research networks (FRNs) have emerged as a promising approach to address these challenges by involving farmers in the research process through co-development and implementation of research, fostering collaboration, and facilitating knowledge sharing through extended networks. FRNs offer an opportunity to promote agroecological practices and this has been demonstrated through the evaluation and adoption of botanical pesticides. Through this approach FRNs have been an effective route for smallholders to reduce synthetic pesticide use, promoting more sustainable farming practices, and enhancing community resilience. Future potential opportunities for FRNs include enabling farmers to adopt interventions that optimise the contribution of natural enemies for pest control and pollination services by improving agricultural landscapes, expanding the cultivation of useful plants for pest management, and conducting research with FRNs on beneficial insects and soil health.
Extracts from Field Margin Weeds Provide Economically Viable and Environmentally Benign Pest Control Compared to Synthetic Pesticides
(Plos One, 2015-11-23) Mkenda, Prisila; Mwanauta, Regina; Stevenson, Philip; Ndakidemi, Patrick; Mtei, Kelvin; Belmain, Steven
Plants with pesticidal properties have been investigated for decades as alternatives to synthetics, but most progress has been shown in the laboratory. Consequently, research on pesticidal plants is failing to address gaps in our knowledge that constrain their uptake. Some of these gaps are their evaluation of their efficacy under field conditions, their economic viability and impact on beneficial organisms. Extracts made from four abundant weed species found in northern Tanzania, Tithonia diversifolia, Tephrosia vogelii, Vernonia amygdalina and Lippia javanica offered effective control of key pest species on common bean plants (Phaseolus vulgaris) that was comparable to the pyrethroid synthetic, Karate. The plant pesticide treatments had significantly lower effects on natural enemies (lady beetles and spiders). Plant pesticide treatments were more cost effective to use than the synthetic pesticide where the marginal rate of return for the synthetic was no different from the untreated control, around 4USD/ha, compared to a rate of return of around 5.50USD/ha for plant pesticide treatments. Chemical analysis confirmed the presence of known insecticidal compounds in water extracts of T. vogelii (the rotenoid deguelin) and T. diversifolia (the sesquiterpene lactone tagitinin A). Sesquiterpene lactones and the saponin vernonioside C were also identified in organic extracts of V. amygdalina but only the saponin was recorded in water extracts which are similar to those used in the field trial. Pesticidal plants were better able to facilitate ecosystem services whilst effectively managing pests. The labour costs of collecting and processing abundant plants near farm land were less than the cost of purchasing synthetic pesticides.
Extracts of Common Pesticidal Plants Increase Plant Growth and Yield in Common Bean Plants.
(MDPI, 2020-01-23) Mkindi, Angela; Tembo, Yolice; Mbega, Ernest; Smith, Amy; Farrell, Iain; Ndakidemi, Patrick; Stevenson, Philip; Belmain, Steven
Common bean () is an important food and cash crop in many countries. Bean crop yields in sub-Saharan Africa are on average 50% lower than the global average, which is largely due to severe problems with pests and diseases as well as poor soil fertility exacerbated by low-input smallholder production systems. Recent on-farm research in eastern Africa has shown that commonly available plants with pesticidal properties can successfully manage arthropod pests. However, reducing common bean yield gaps still requires further sustainable solutions to other crop provisioning services such as soil fertility and plant nutrition. Smallholder farmers using pesticidal plants have claimed that the application of pesticidal plant extracts boosts plant growth, potentially through working as a foliar fertiliser. Thus, the aims of the research presented here were to determine whether plant growth and yield could be enhanced and which metabolic processes were induced through the application of plant extracts commonly used for pest control in eastern Africa. Extracts from and were prepared at a concentration of 10% and applied to potted bean plants in a pest-free screen house as foliar sprays as well as directly to the soil around bean plants to evaluate their contribution to growth, yield and potential changes in primary or secondary metabolites. Outcomes of this study showed that the plant extracts significantly increased chlorophyll content, the number of pods per plant and overall seed yield. Other increases in metabolites were observed, including of rutin, phenylalanine and tryptophan. The plant extracts had a similar effect to a commercially available foliar fertiliser whilst the application as a foliar spray was better than applying the extract to the soil. These results suggest that pesticidal plant extracts can help overcome multiple limitations in crop provisioning services, enhancing plant nutrition in addition to their established uses for crop pest management.
Farmers’ insights and practices on sustainable soil nutrient and pest management in semi-arid Eastern Africa
(MDPI, 2025-03-12) Ojuu, David; Mkindi, Angela; Meya, Akida; Giliba, Richard; Vanek, Steven; Belmain, Steven
The need to increase agricultural production for food, fiber, and feed for a growing population is a global call. Sub-Saharan Africa currently experiences declining soil fertility and increasing pest pressures affecting agricultural production. Soil fertility and pest management practices tend to vary greatly among smallholder farmers due to farm-based limitations, attitudes, and perceptions. Using focus group discussions and individual farmer interviews, we evaluated the socio-economic factors influencing the production and utilization of nutrient resources by smallholder farmers. We also assessed factors for pest prevalence and management by smallholder farmers. We observed that the major organic nutrient fertilizer resources used by farmers are farmyard manure and crop residue recycling. The production and utilization of organic nutrient fertilizer resources vary according to agroecological zone, influenced by livestock ownership, grazing management, and farmer organization; Farmer Research Network farmers show optimal use of nutrient resources compared to non-Farmer Research Network farmers. Pest problems varied across agroecologies and were influenced by field management gradients. We noted that FRN farmers used ecologically relevant pest management approaches more frequently than non-FRN farmers. Our findings on nutrient resources and pest management highlight context-specific issues to leverage to promote agroecological approaches for agricultural productivity and resilient semi-arid landscapes.
Field Margin Plants Support Natural Enemies in Sub-Saharan Africa Smallholder Common Bean Farming Systems
(MDPI, 2022-03-28) Ndakidemi, Baltazar; Mbega, Ernest; Ndakidemi, Patrick; Belmain, Steven; Arnold, Sarah; Woolley, Victoria; Stevenson, Philip
Flower-rich field margins provide habitats and food resources for natural enemies of pests (NEs), but their potential, particularly in the tropics and on smallholder farms, is poorly understood. We surveyed field margins for plant-NE interactions in bean fields. NEs most often interacted with Bidens pilosa (15.4% of all interactions) and Euphorbia heterophylla (11.3% of all interactions). In cage trials with an aphid-infested bean plant and a single flowering margin plant, the survival of Aphidius colemani, the most abundant parasitoid NE in bean fields, was greater in the presence of Euphorbia heterophylla than Bidens pilosa, Tagetes minuta, and Hyptis suaveolens. UV-fluorescent dye was applied to flowers of specific field margin plant species and NE sampled from within the bean crop and field margins using sweep-netting and pan-traps respectively. Captured insects were examined for the presence of the dye, indicative of a prior visit to the margin. Lady beetles and assassin bugs were most abundant in plots with B. pilosa margins; hoverflies with T. minuta and Parthenium hysterophorus margins; and lacewings with T. minuta and B. pilosa margins. Overall, NE benefitted from field margin plants, and those possessing extra floral nectaries had an added advantage. Field margin plants need careful selection to ensure benefits to different NE groups.
Field Margin Vegetation in Tropical African Bean Systems Harbours Diverse Natural Enemies for Biological Pest Control in Adjacent Crops
(MDPI, 2019-11-14) Mkenda, Prisila; Ndakidemi, Patrick; Stevenson, Philip; Arnold, Sarah; Belmain, Steven; Chidege, Maneno; Gurr, Geo
Non-crop vegetation around farmland can be valuable habitats for enhancing ecosystem services but little is known of the importance of field margins in supporting natural enemies of insect pests in tropical agriculture. This study was conducted in smallholder bean fields in three elevation zones to assess the importance of field margin vegetation to natural enemy populations and movement to the bean crop for biological pest control. The pests and natural enemies were assessed using di erent coloured water pan traps (to ensure the capture of insects with di erent colour preferences) and the interactions of the two arthropod groups with the margin vegetation and their movement to the bean crop were monitored using fluorescent dye. Sentinel plants were used to assess predation and parasitism levels. A total of 5003 natural enemies were captured, more in the field margin than within the bean field for low and mid elevation zones, while in the high elevation zone, they were more abundant within the bean field. Pests were more abundant in the crop than margins for all the elevation zones. The use of a dye applied to margin vegetation demonstrated that common natural enemy taxa moved to the crop during the days after dye application. The proportion of dye-marked natural enemies (showing their origin to be margin vegetation) sampled from the crop suggest high levels of spatial flux in the arthropod assemblage. Aphid mortality rates (measured by prey removal and parasitism levels on sentinel plants) did not di er between the field edges and field centre in any of the three elevation zones, suggesting that for this pest taxon, the centre of the fields still receive comparable pest control service as in the field edges. This study found that field margins around smallholder bean fields are useful habitats to large numbers of natural enemy taxa that move to adjacent crops providing biological pest control service.
Field margins and botanical insecticides enhance Lablab purpureus yield by reducing aphid pests and supporting natural enemies
(John Wiley and Sons Inc, 2022-05-20) Ochieng, Lawrence; Ogendo, Joshua; Bett, Philip; Nyaanga, Jane; Cheruiyot, Erick; Mulwa, Richard; Arnold, Sarah; Belmain, Steven; Stevenson, Philip
Botanical insecticides offer an environmentally benign insect pest management option for field crops with reduced impacts on natural enemies of pests and pollinators while botanically rich field margins can augment their abundance. Here, we evaluated the non-target effects on natural enemies and pest control efficacy on bean aphids in Lablab of three neem- and pyrethrum-based botanical insecticides (Pyerin75EC®, Nimbecidine® and Pyeneem 20EC®) and determine the influence of florally rich field margin vegetation on the recovery of beneficial insects after treatment. The botanical insecticides were applied at the early and late vegetative growth stages. Data were collected on aphids (abundance, damage severity and percent incidence) and natural enemy (abundance) both at pre-spraying and post-spraying alongside Lablab bean yield. The efficacy of botanical insecticides was similar to a synthetic pesticide control and reduced aphid abundance by 88% compared with the untreated control. However, the number of natural enemies was 34% higher in botanical insecticide-treated plots than in plots treated with synthetic insecticide indicating that plant-based treatments were less harmful to beneficial insects. The presence of field margin vegetation increased further the number of parasitic wasps and tachinid flies by 16% and 20%, respectively. This indicated that non-crop habitats can enhance recovery in beneficial insect populations and that botanical insecticides integrate effectively with conservation biological control strategies. Higher grain yields of 2.55–3.04 and 2.95–3.23 t/ha were recorded for both botanical insecticide and synthetic insecticide in the presence of florally enhanced field margins in consecutive cropping seasons. Overall, these data demonstrated that commercial botanical insecticides together with florally rich field margins offer an integrated, environmentally benign and sustainable alternative to synthetic insecticides for insect pest management and increased productivity of the orphan crop legume, Lablab.
Identifying the right plants for diverse biocontrol agents in tropical smallholder bean farming systems
(African Journals OnLine (AJOL), 2022-10-20) Mkenda, ‪Prisila; Ndakidemi, Patrick; Stevenson, Philip; Arnold, Sarah; Belmain, Steven; Darbyshire, Iain; Gurr, Geoff
Biocontrol agents such as predators, parasitoids and pathogens potentially regulate crop pests populations. The agents feed directly on the pests, oviposit in the pest body or cause disease in the pest. While biocontrol has become a commercial enterprise in temperate horticulture, there is much less information on the biocontrol agents present in smallholder agricultural systems in the tropics and little knowledge about the importance of plant diversity in supporting their biocontrol activities. A standardized botanical survey walk combined with observations of plant insect interactions was conducted on field margin vegetation of 24 smallholder fields of common beans (Phaseolus vulgaris L.) in three elevation zones of a tropical ecosystem. Sweep nets were also used to capture the biocontrol agents and stored in 70% ethanol for detailed taxonomy where identification in the field was not possible. A wide range of biocontrol agents interacting with the field margin plants, particularly flowering forbs were revealed. The most preferred field margin plants were Ageratum conyzoides, Commelina benghalensis, Pennisetum purpureum, Panicum maximum and Tripsacum sp. The most common biocontrol agents found to interact with the field margin plants were spiders (Araneae), long-legged flies (Dolichopodidae), predatory and parasitic wasps (Ichneumonids and braconids), hoverflies (Syrphidae) and assassin bugs (Reduviidae). Preferences of the biocontrol agents to certain plant species were similar across all three zones, indicating the importance of such plants in terms of food resources, shelter or nesting sites. The preference of the biocontrol agents to some plant species indicates the need to identify the specific benefits of these species to the biocontrol agents to determine whether non-crop habitat manipulation might enhance natural pest regulation.Biocontrol agents such as predators, parasitoids and pathogens potentially regulate crop pests populations. The agents feed directly on the pests, oviposit in the pest body or cause disease in the pest. While biocontrol has become a commercial enterprise in temperate horticulture, there is much less information on the biocontrol agents present in smallholder agricultural systems in the tropics and little knowledge about the importance of plant diversity in supporting their biocontrol activities. A standardized botanical survey walk combined with observations of plant insect interactions was conducted on field margin vegetation of 24 smallholder fields of common beans (Phaseolus vulgaris L.) in three elevation zones of a tropical ecosystem. Sweep nets were also used to capture the biocontrol agents and stored in 70% ethanol for detailed taxonomy where identification in the field was not possible. A wide range of biocontrol agents interacting with the field margin plants, particularly flowering forbs were revealed. The most preferred field margin plants were Ageratum conyzoides, Commelina benghalensis, Pennisetum purpureum, Panicum maximum and Tripsacum sp. The most common biocontrol agents found to interact with the field margin plants were spiders (Araneae), long-legged flies (Dolichopodidae), predatory and parasitic wasps (Ichneumonids and braconids), hoverflies (Syrphidae) and assassin bugs (Reduviidae). Preferences of the biocontrol agents to certain plant species were similar across all three zones, indicating the importance of such plants in terms of food resources, shelter or nesting sites. The preference of the biocontrol agents to some plant species indicates the need to identify the specific benefits of these species to the biocontrol agents to determine whether non-crop habitat manipulation might enhance natural pest regulation.
Insect pollination is important in a smallholder bean farming system.
(PeerJ, 2020-10-20) Elisante, Filemon; Ndakidemi, Patrick; Arnold, Sarah; Belmain, Steven; Gurr, Geoff; Darbyshire, Iain; Xie, Gang; Stevenson, Philip
Many crops are dependent on pollination by insects. Habitat management in agricultural landscapes can support pollinator services and even augment crop production. Common bean ( L.) is an important legume for the livelihoods of smallholder farmers in many low-income countries, particularly so in East Africa. While this crop is autogamous, it is frequently visited by pollinating insects that could improve yields. However, the value of pollination services to common beans (Kariasii) yield is not known. We carried out pollinator-exclusion experiments to determine the contribution of insect pollinators to bean yields. We also carried out a fluorescent-dye experiment to evaluate the role of field margins as refuge for flower-visitors. Significantly higher yields, based on pods per plant and seeds per pod, were recorded from -pollinated and -pollinated flowers compared to plants from which pollinators had been excluded indicating that flower visitors contribute significantly to bean yields. Similarly, and -pollinated plants recorded the highest mean seed weight. Extrapolation of yield data to field scale indicated a potential increase per hectare from 681 kg in -pollinated beans to 1,478 kg in -pollinated beans indicating that flower visitors contributed significantly to crop yield of beans. Our marking study indicated that flower-visiting insects including bees, flies and lepidopterans moved from the field margin flowers into the bean crop. Overall, these results show that insect pollinators are important for optimising bean yields and an important food security consideration on smallholder farms. Field margin vegetation also provides habitat for flower-visiting insects that pollinate beans. Hence, non-crop habitats merit further research focusing on establishing which field margin species are most important and their capacity to support other ecosystem services such as natural pest regulation or even pests.
Insecticidal activity of Tithonia diversifolia and Vernonia amygdalina
(Elsevier Ltd, 2017-08-26) Stevensona, Philip; Greena, Paul; Belmain, Steven; Ndakidemi, Patrick; Farrell, Iain
The diversity of synthetic pesticides has been reduced through regulation especially in the European Union, leading to a resurgence of interest in natural plant products for pest control. Here we investigated two Asteraceae species, Tithonia diversifolia and Vernonia amygdalina that are used by farmers in Africa in bio-rational pest control to determine the chemical basis of activity against pests of stored legumes and identify plant compounds with commercial potential. The cowpea beetle, Callosobruchus maculatus, an ubiquitous pest of African stored grain legumes, was exposed to extracts of both plant species at 10, 1 and 0.1% w/v and fractions of these extracts at representative concentrations. Extracts and fractions were toxic to recently emerged adults, but did not reduce oviposition by those females that survived. The sesquiterpene, tagitinin A, was isolated from one of the active fractions and identified using H1 and C13-NMR and shown also be toxic to C. maculatus and so partially explains the activity of the whole plant. Other compounds in the active fractions were identified, at least to structural class, using high resolution mass spectroscopy (HRESI-MS). Sequiterpenes and flavones were common to fractions from both plants. Stigmostane steroidal saponins were the most abundant secondary metabolites in V. amygdalina.
Intercropping and diverse field margin vegetation suppress bean aphid (Homoptera: Aphididae) infestation in dolichos (Lablab purpureus L.)
(Polska Akademia Nauk, 2021-10-12) Mwani, Christine; Nyaanga, Jane; Cheruiyot, Erick; Ogendo, Joshua; Bett, Philip; Mulwa, Richard; Stevenson, Philip; Arnold, Sarah; Belmain, Steven
Dolichos (Lablab purpureus L.) is a drought tolerant legume used as food/feed and improvement of soil fertility. The production of dolichos in Kenya, Nakuru County is however limited by insect pests like bean aphids, pod borers and whiteflies. Field studies were conducted to determine the effect of cropping systems (dolichos monocrop and maize-dolichos intercrop) and field margin vegetation on bean aphids and their natural enemies. The experiment was conducted in Njoro (high field margin vegetation) and Rongai (low field margin vegetation) during May–December 2019 and March−November 2020 cropping seasons. Bean aphid percent incidence, severity of damage and abundance was assessed at seedling, early vegetative, late vegetative and flowering dolichos growth stages. The populations of natural enemies in the plots and field margin vegetation were monitored using pan traps and sweep nets. Species diversity and composition of the field margin vegetation was determined using a quadrat. Results showed that location and cropping system had significant effects on bean aphid infestations. A high bean aphid incidence (38.13%) was observed in Njoro compared to Rongai (31.10%). Dolichos monocrop had significantly higher bean aphid infestation (51.63%) than the maize-dolichos intercrop system (24.62%). A highly diverse Shannon-weaver index was observed in Rongai (1.90) compared to Njoro (1.67). Dolichos monocrop had a more diverse Shannon-weaver index (1.8) than the maizedolichos intercrop system (1.7). Rongai had the most abundant annual and perennial field margin vegetation species. The field margin species richness and diversity were higher in Rongai (81%) than in Njoro (54%). The findings of this study have demonstrated that a maize-dolichos intercrop in Rongai can reduce bean aphid damage in dolichos.
Invasive weeds with pesticidal properties as potential new crops
(Elsevier, 2017) Belmain, Steven; Mkindi, Angela; Mpumi, Nelson; Tembob, Yolice; Stevenson, Phillip; Ndakidemi, Patrick; Mtei, Kelvin; Machunda, Revocatus
Plants with pesticidal properties have been investigated for decades as alternatives to synthetics, but only a handful have been commercialised and developed as non-food cash crops. One of the reasons why pesticidal plants are failing to deliver new pesticidal products is that they are often not evaluated under field conditions by farmers. Furthermore, many aspects of pesticide use related to environmental safety, such as their impact on beneficial organisms, remain under-evaluated. With a view to overcoming these bottlenecks, extracts made from six abundant weed species found across sub-Saharan Africa (Bidens pilosa, Lantana camara, Lippia javanica, Tithonia diversifolia, Tephrosia vogelii and Vernonia amygdalina) were evaluated in on-station and on-farm trials over two years (2015 and 2016) in two different countries (Tanzania and Malawi) on common bean plants (Phaseolus vulgaris). All plant species offered effective control of key pest species that was comparable in terms of harvested bean yield to a synthetic pyrethroid. Furthermore, the plant pesticide treatments had significantly lower negative effects on natural enemies (hover flies, lacewings, ladybird beetles and spiders). Thus, pesticidal plants were better able to support ecosystem services whilst effectively managing pests. Small holder farmer rankings on their perceived efficacy of the different plant species indicated that T. vogelii was the most preferred and effective, achieving bean yields as good as the synthetic, if not better. As T. vogelii is fast growing with a wellknown and understood phytochemistry, it is an excellent candidate for commercial development to supplement pyrethrum production by African small holder farmers.
Multiple ecosystem services from field margin vegetation for ecological sustainability in agriculture: scientific evidence and knowledge gaps.
(PubMed, 2019-11-28) Mkenda, Prisila; Ndakidemi, Patrick; Mbega, Ernest; Stevenson, Philip; Arnold, Sarah; Gurr, Geoff; Belmain, Steven;
Background Field margin and non-crop vegetation in agricultural systems are potential ecosystem services providers because they offer semi-natural habitats for both below and above ground animal groups such as soil organisms, small mammals, birds and arthropods that are service supplying units. They are considered as a target area for enhancing farm biodiversity. Methodology To explore the multiple potential benefits of these semi-natural habitats and to identify research trends and knowledge gaps globally, a review was carried out following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. A total of 235 publications from the year 2000 to 2016 in the Scopus and Web of Science databases were reviewed. Results The literature showed an increasing trend in the number of published articles over time with European studies leading in the proportion of studies conducted, followed by North America, Asia, South America, Africa and Australia. Several functional groups of organisms were studied from field margin and non-crop vegetation around agricultural lands including natural enemies (37%), insect pests (22%), birds (17%), pollinators (16%), soil macro fauna (4%) and small mammals (4%). Ecosystem services derived from the field margin included natural pest regulation, pollination, nutrient cycling and reduced offsite erosion. Some field margin plants were reported to host detrimental crop pests, a major ecosystem dis-service, potentially leading to increased pest infestation in the field. Conclusion The majority of studies revealed the importance of field margin and non-crop vegetation around arable fields in enhancing ecosystem biodiversity. Promotion of field margin plants that selectively enhance the population of beneficial organisms would support sustainable food security rather than simply boosting plant diversity. Our analyses also highlight that agro-ecological studies remain largely overlooked in some regions.
Natural Pest Regulation and Its Compatibility with Other Crop Protection Practices in Smallholder Bean Farming Systems
(MDPI, 2021-08-20) Ndakidemi, Baltazar; Mbega, Ernest; Ndakidemi, Patrick; Stevenson, Philip; Belmain, Steven; Arnold, Sarah; Woolley, Victoria
Common bean (Phaseolus vulgaris) production and storage are limited by numerous con- straints. Insect pests are often the most destructive. However, resource-constrained smallholders in sub-Saharan Africa (SSA) often do little to manage pests. Where farmers do use a control strategy, it typically relies on chemical pesticides, which have adverse effects on the wildlife, crop pollinators, natural enemies, mammals, and the development of resistance by pests. Nature-based solutions —in particular, using biological control agents with sustainable approaches that include biopesticides, resistant varieties, and cultural tools—are alternatives to chemical control. However, significant barriers to their adoption in SSA include a lack of field data and knowledge on the natural enemies of pests, safety, efficacy, the spectrum of activities, the availability and costs of biopesticides, the lack of sources of resistance for different cultivars, and spatial and temporal inconsistencies for cultural methods. Here, we critically review the control options for bean pests, particularly the black bean aphid (Aphis fabae) and pod borers (Maruca vitrata). We identified natural pest regulation as the option with the greatest potential for this farming system. We recommend that farmers adapt to using biological control due to its compatibility with other sustainable approaches, such as cultural tools, resistant varieties, and biopesticides for effective management, especially in SSA.