1.1 Climate Change and Impact on African Agriculture
The Earth’s climate has become increasingly warmer, most likely from increasing greenhouse gas emissions. Climate change—a phenomenon synonymous with global warming and the greenhouse effect—is projected to continue. Major effects of climate change will be (1) a rise of 1.5°–5.8°C in the mean temperature by the end of the twenty-first century; (2) an increase in the frequency of droughts; (3) an increase in sea levels and frequency of floods and heavy rains; and (4) an alteration of wind directions (IPCC 2001, 2014). Predictions forecast higher growing season temperatures in the tropics and subtropics that will exceed the most extreme seasonal temperatures recorded in the 1900s. Climate change is expected to exacerbate the already serious challenges to food security and economic development, especially on the African continent, where people are already struggling to meet challenges posed by existing climatic variability. Some 330 million people live in extreme poverty in sub-Saharan Africa (SSA), with 70% of the population surviving by subsistence agriculture (Hellmuth et al. 2007). Climate change will greatly affect crop productivity as overall yields may fall because of two primary factors—warming and drying—as well as increased presence and spread of insect pests. This makes adaptation to climate change especially relevant for Africa. Climate-derived information is most likely to improve development outcomes when it is integrated into a framework for decision making to specific risks (Thomas and Twyman 2005; Hellmuth et al. 2007).
1.2 Climate Change Impacts on Arthropod Pests and Biological Control
On average, 30–50% of the yield losses in agricultural crops are caused by pests despite the application of pesticides to control them (Oerke 2006). Climate change will aggravate these already serious challenges to food security due to increasing pest problems and related losses in crop yield and quality. As exothermic organisms, insect pests cannot internally regulate their own temperature and depend on the temperature to which they are exposed in the environment. Under climate change, then, temperature is the dominant abiotic factor directly affecting herbivorous insects. Any temperature increase—depending on a species’ optimal temperature of development—is expected to magnify pest pressure in agricultural systems through:
- Range expansion of native pests and invasion by new pests
- Accelerated pest development leading to more pest generations per season and year
- Disruption of the temporal and geographical synchronization of pests and beneficial insects that increases the risk of pest outbreaks
- Promotion of minor pests to primary pests through reduced host tolerance and changes in landscape characteristics and land-use practices
- Increase in the susceptibility to pests in drought-stressed plants.
Depending on the complexity and species richness, agro-ecosystems can have good potential to provide a high level of natural biological control; hence ecosystem complexity can increase ecosystem resilience to pest outbreaks. Several studies indicate, however, that climate change can dissociate natural enemy (predator/parasitoid)-pest relationships, because of a higher sensitivity of higher trophic levels to climatic variability or of different temperature optima compared with pests. In this respect, divergences in the thermal preferences of pests and associated natural enemies can lead to a disruption of the temporal or geographical synchronization, increasing the risks of host outbreaks. This might also reduce the efficacy of successful classical biocontrol programs.