Field margin Plants support arthropod natural enemies in smallholder common bean farming systems in northern Tanzania

A Dissertation Submitted in Fulfilment of the Requirements for the Degree of Doctor of Philosophy in Life Sciences of the Nelson Mandela African Institution of Science and TechnologyField margin plants provide habitats and food resources for natural enemies of pests (NEs), but their potential is poorly understood, particularly in the tropics and on smallholder farms. The experiments were conducted to test the potential of field margin plants on NEs. Sentinel plants were developed to collect Aphis fabae and Maruca vitrata parasitoids. Aphidius colemani was identified as the primary parasitoid of A. fabae. The dominant M. vitrata larval parasitoids were the Braconidae and Dolichogenidea, while the Platygastridae were the abundant egg parasitoids. The survey of field margins for plant-NE interactions in bean fields found that NEs most often interacted with Bidens pilosa (15.4%) and Euphorbia heterophylla (11.3%). Flowering plant species (Bidens pilosa, Lantana camara, Euphorbia heterophylla and Ageratum conyzoides) supported NEs out of bean growing season. In cage trials with an aphid- infested bean plant and a single flowering margin plant, the survival of A. colemani was more significant in the presence of E. heterophylla than B. pilosa, Tagetes minuta and Hyptis suaveolens. UV-fluorescent dye was applied to flowers of specific field margin plant species and NE was 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 abundant in plots with B. pilosa margins, hoverflies with T. minuta and Parthenium hysterophorus margins, and lacewings with T. minuta and B. pilosa margins. NEs were also sampled from high and low plant diversity bean fields using sweep netting and coloured sticky traps, comparing monocropped and intercropped farms. Overall, high-plant diversity fields had higher NEs than low-diversity fields. The field margin had a significantly higher number of NEs than the crop field. However, marginally higher populations of NEs in intercropping than in monocropping were observed, although the effect was not significant. To confirm that NE communities on farms predated Aphis fabae, we extracted and amplified A. fabae DNA from predatory insects. Fourteen lady beetle larvae, two lacewing larvae, and one assassin bug analyzed were found to contain A. fabae DNA, indicating all these groups can regulate the significant aphid pest of beans, A. fabae. A. colemani was a parasitoid that emerged from several non-aphid species collected from the field margins. Overall, NEs benefitted from field margin plants; those possessing extra floral nectaries had an added advantage. Thus, smallholder farmers protect the field margins for the added benefit of natural pest regulation in their fields and thus for food security and enhancing their livelihoods

Plant-rich field margins influence natural predators of aphids more than intercropping in common bean

Field margins support important ecosystem services including natural pest regulation. We inves-tigated the influence of field margins on the spatial and temporal distribution of natural enemies (NEs) of bean pests in smallholder farming systems. We sampled NEs from high and low plant diversity bean fields using sweep netting and coloured sticky traps, comparing monocropped and intercropped farms. NEs collected from within crops included predatory bugs, lacewings, pred-atory flies, parasitic flies, parasitic wasps, lady beetles, and a range of other predatory beetles; with the most dominant group being parasitic wasps. Overall, high plant diversity fields had a higher number of NEs than low-diversity fields, regardless of sampling methods. The field mar-gin had a significantly higher number of lacewings, parasitic wasps, predatory bugs, syrphid flies, and other predatory beetles relative to the crop, but beneficial insects were collected throughout the fields. However, we observed marginally higher populations of NEs in intercrop-ping than in monocropping although the effect was not significant in both low and high plant di-versity fields. We recommend smallholder farmers protect the field margins for the added benefit of natural pest regulation in their fields

Field margin plants support natural enemies in sub-Saharan Africa smallholder common bean farming systems

Flower-rich field margins provide habitat 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, 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 NEs 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; lacewings with T. minuta and B. pilosa margins. Overall, NEs 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

Natural pest regulation and its compatibility with other crop protection practices in smallholder bean farming systems

Common bean (Phaseolus vulgaris) production and storage are limited by numerous constraints. 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

Ecosystem services for crop protection in bean fields in Moshi rural, along the slopes of Mt. Kilimanjaro Northern Tanzania

A Dissertation Submitted in Partial Fulfilment of the Requirements for the Degree of Master’s in Environmental Science and Engineering of the Nelson Mandela African Institution of Science and Technology, Arusha, TanzaniaThe natural ecosystem, in and around bean fields potentially offer beneficial services that assist bean productivity. This study was conducted to investigate the distribution of beneficial invertebrates and plants and their conducive environmental conditions in bean fields in Moshi rural, along the slopes of Mt. Kilimanjaro Northern Tanzania. Four farms were chosen on the basis of four factors which were elevation, crop diversity (mixed crop farming), forestation level (farming in grasslands, woodlands and bush land areas), and cropping intensity (most land converted to farming with little bush land, farm-fallow mosaic, small areas of farming with mostly bush/fallow land). Beneficial insects were collected monthly using pan traps. Five traps were placed in the crop plants and the other five traps were placed in the field margin. The insects collected were identified to the functional group level. Plants found associated with beneficial insects were also collected for identification. Monitoring of the insects’ visits to plants was done and photos were taken. It was observed that elevation, time of the year (month), field margin plant species, rainfall and temperature affected the type, richness and diversity of invertebrate communities. There are great spatio-temporal differences in invertebrates’ groups associated with ecosystems services delivery, particularly pollination and pest management functions. The results indicated that there was significant difference (P ≤ .05) among sites in terms of the abundance and richness of invertebrates present. Rainfall and temperature had a potential influence on invertebrates’ groups. In most cases, the highest populations of insects were found in the field margins and edges (P ≤ .05). From this study it can be recommend that it is essential to preserve field margins and edges, cultivate plant species that attract beneficial insects and devise agro-environment strategies to support them

The Potential of Common Beneficial Insects and Strategies for Maintaining Them in Bean Fields of Sub Saharan Africa

This research article was published by Scientific Research Publishing in 2016Beneficial insects provide natural ecosystem services such as biological control of pests, soil for mation, nutrient cycling and pollination of plants. Beneficial insects include pollinators important in the essential pollination process of all plants, and natural enemies of pests such as parasitoids and predators which are important in the suppression of pest damage to crops. Knowledge on management techniques to attract beneficial insects in the agricultural fields is a way forward to enhance agro ecosystems for increased crop production. Therefore, proper understanding and identification of natural enemies, as well as pollinators in agricultural fields, is essential in pro moting biological control and pollination activity. Natural enemies and pollinators, within legume fields, play a key role in ensuring sustainable production, especially in smallholder farms. There is a limited understanding of beneficial insects and the ecosystem services they offer to the agricul tural production process in much of sub-Saharan Africa. This paper reviewed and provided exist ing knowledge on beneficial insects in bean fields. This will give the basis for research on benefi cial insects in bean fields and practices that encourage their population

Natural Pest Regulation and Its Compatibility with Other Crop Protection Practices in Smallholder Bean Farming Systems

Common bean (Phaseolus vulgaris) production and storage are limited by numerous constraints. 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

Impacts of synthetic and botanical pesticides on beneficial insects

This research article was published by Scientific Research Publishing in 2016Sustainable methods to control insect pests that affect crop yield have become a great challenge to mainly smallholder farmers. Beneficial insects in agricultural fields play an important role in natural pest control and pollination. The use of synthetic and botanical pesticides has detrimental effects to both natural enemies and pollinators in agricultural fields. The pesticides affect the survival of a range of life cycle stages, reductions in reproductive capacity, changes in the suitability of hosts for parasitising or predation, reduced emergence of parasitoids from sprayed host eggs and cause direct mortality. This has caused a serious menace to biological control agents and pollinators. When natural enemies are reduced, even more serious consequences may result for pest population dynamics which include the phenomena of resurgence and eruption of secondary pests. The decrease in pollinators reduces agricultural productivity. This review aims at exploring the side effects of synthetic and botanical pesticides on beneficial insects to give the basis for research on the negative impacts of synthetic and botanical pesticides on these insects. This information will assist in optimizing the use of pesticides in integrated pest management programmes by employing more sustainable and ecosystem benign practices such as the use of right dosage and selective pesticides in agricultural fields

The diversity of aphid parasitoids in East Africa and implications for biological control

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