Browsing by Author "Otieno, Nickson Erick"
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- ItemAssessment of farming systems and cover configuration options that enhance natural regulation of herbivorous arthropod abundance in maize-fields(Stellenbosch : Stellenbosch University, 2018-12) Otieno, Nickson Erick; Jacobs, Shayne Martin; Pryke, James S.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.ENGLISH ABSTRACT: Maize, Zea mais, is grown globally and is a leading staple crop in sub-Saharan Africa, where it crucially sustains many household economic and nutritional needs, and the continent’s food security. However, its production is curtailed by damage from a range of herbivorous arthropods, undermining its potential to fulfil increasing demand from a growing population. In Kenya, maize is produced primarily by small-scale subsistence farmers who have limited economic capacity for commercially-based arthropod herbivore control. Whereas the scale of future crop arthropod damage is projected to increase due to global warming, low economies of operational scale undermine many farmers’ ability to increase their response investment to forestall anticipated crop losses. This calls for measures for crop-field arthropod control that are affordable yet affective for sustainable maize production. I investigated a range of agronomic management practices that may be applied in fostering natural suppression of arthropod herbivore abundance across 16 non-Bt maize-fields in western Kenya. I assessed how structural configurations and cover elements including hedgerows, on-farm trees, crop-cover patterns, woodlots and maize cover proportion enhance farm-level habitat complexity to attract predatory arthropods and insectivorous birds for top-down suppression of herbivorous arthropods. I compared effects of these variables on abundance, richness and diversities of arthropod and birds species between organic and conventional farming systems and between monocultured maize versus maize inter-cropped with legume crops. To assess potential for herbivorous arthropod reduction rates, I analysed δ13C and δ 15N stable isotope signatures to track maize carbon through herbivorous arthropods to arthropod predators, and also established a bird exclusion experiment to test insectivorous birds’ contribution to reducing arthropod abundance. By grouping farms into structural clusters, I further tested how arthropod and bird assemblage turnovers differed between local farm-level and wider spatial scales and along a heterogeneity gradient. Organic rather than conventional farming was more supportive of local-scale arthropod abundance, together with inter-copping, but not at wider spatial levels. However, organic farming was less important than crop diversity in boosting insectivorous bird abundance and richness. Herbivorous arthropods were significantly attracted to fields with higher maize cover proportions especially on conventional farms, suggesting susceptibility of monocultured maize to proliferous arthropod herbivory. Higher hedgerow volume, tree densities and larger woodlots enhanced all arthropod guild and bird aggregations at both spatial scales. Although the bird exclusion experiment proved insectivorous birds’ linkage to herbivorous arthropod suppression at local-farm level, this effect was not evident at wider spatial scales. Stable isotope analyses revealed a stronger predator-herbivore trophic linkage under inter-cropping systems, with lepidopteran herbivores the most significant consumers of both maize and legumes. On the other hand, ants showed the best capacity to suppress maize-consuming arthropods while wasps and beetles would best reduce legume consumers. The findings demonstrate that there is a wide range of farm-level habitat management practices for enhancing habitat complexity to boost natural top-down herbivore suppression across maize-fields, but greater effectiveness is achievable through synergistic application of measures rather than individualistic approaches. Furthermore, a multi-spatial scale strategy in applying appropriate techniques would maximize landscape resilience against herbivorous arthropods.