Agrobiodiversity for Biological Pest Control in Sub-Saharan Africa

Abstract

Sub-Saharan Africa (SSA) currently has the fastest global population growth and urbanization rates respectively put at 2.7 % and 40 %. Crop yields in the region have however stagnated over the past five decades at about 1 tonne per hectare. The increasing demand for human food/livestock feed and financial gains continue to drive extensive conversion of land use to agriculture, agricultural land expansion and intense/unsustainable use of agropastoral practices such as annual monocultures, excessive agrochemicals/soil contamination, overcultivation, overgrazing, uncontrolled bush fires, unskilled irrigation, etc. that lead to land degradation. Land degradation in the forms of soil and water erosion, soil nutrient depletion, deforestation, desertification, etc. are common in the region, and may further exacerbate in the face of increasing climate change effects. Put together, these events greatly cause the destruction of natural and semi-natural habitats in the region, and in turn, increasingly threatens the sustainability of agrobiodiversity and associated ecosystem functions (i.e., biological control) and services (i.e., insect pest population regulation). This synthesis of literature highlighted the importance of natural/semi-natural habitats in agricultural ecosystems to the survival, fitness and effectiveness of natural enemies (i.e., predators and parasitoids) against agricultural insect pests. The causes and consequences of fragmentation/loss of these habitats, and also agroecosystem simplification were further accentuated. Natural enemies increasingly face limited resources or life-support functions in simplified agroecosystems, wherein natural enemies richness/diversity and activities tend to be low. Conversely, evidence increasingly shows that agricultural landscapes with more permanent/less disturbed, greater spatio-temporal and interconnected natural/semi-natural habitats hold more potential for sustaining agrobiodiversity as well as natural enemy diversity and associated biological control functions (i.e., predation and parasitism). Agroecosystem simplification, largely due to anthropogenic pressures is currently massive in SSA, and may continue to drastically increase in the future. Urgent proactive actions are therefore needed to stall and reverse this ugly trend. There is, however, dearth of information on the effects of agroecosystem simplification on agrobiodiversity sustainability as well as the diversity, survival and antagonistic actions or impact of natural enemies against agricultural insect pests. This review concludes by underscoring the need for future studies in the region to increase understanding on the effects of non-cultivated habitats destruction at different scales, land degradation and climate change on agrobiodiversity sustainability, agroecosystem stability, sustainability of natural enemy diversity and effective biological control function against insect pests and agricultural productivity.