Enhancing crop diversity and ecosystem services to promote biological control of fall armyworm in smallholder cropping systems

Smallholder farming communities in sub-Saharan Africa are particularly vulnerable to crop losses to pests because they generally cannot afford pesticides and as subsistence farmers, they depend directly on the crops for their food security. Fall armyworm has recently invaded and rapidly spread across large areas of Africa, where it has become a major threat to agriculture and sustainable food production. This invasion is a serious and growing threat to food security and livelihoods and already affects at least 400,000 ha causing estimated crop losses worth $3 billion a year.

Our project will employ a four-pronged attack on the fall armyworm, utilising the natural defence mechanisms of the crop and companion plants. Firstly, we will assess the natural resistance levels of the maize millet and sorghum crops available to the farmers to determine which varieties would be most robust against the fall armyworm. We will then attempt to drive pests away from the main crop using a repellent intercrop (push), whilst attracting them to alternative locations with trap plants (pull). This technique is known as a "Push-Pull" companion cropping system and is used currently, successfully, against stemborer pests. Finally, we will attempt to utilise the defence mechanism of other companion plants to bring in local predators of the crop pet. These 'early herbivore varieties' are able to detect insect eggs that have been laid on them and emit odours to attract the natural enemies of the pests to the area where the crop is being cultivated. This novel design of pest management based on the four strategies of resist, expel, trap and kill should provide a novel cropping system which can withstand attack by fall army worm and other major pests.

Design of such a system requires a detailed understanding of the predators and parasites that are the key natural enemies of the invasive fall armyworm in Kenya. Therefore, a major part of this project will be to understand the current pest and predator relationship where the crops are being grown. Once determined, we will be able to test how such companion cropping and early alert crops could mitigate crop losses to the fall army worm using crops that are readily available to the farmers in Kenya. Such a system could only be generated through close partnership with the local farmers. We will co-design solutions with them so that that we can be assured from the onset that the novel cropping system that is created is not just appropriate for their requirements but can be feasibly implemented with the resources available to them.

Fall armyworm (FAW), S. frugiperda, biology and behaviour on different farmer-preferred crop varieties will be measured in bioassays to assess constitutive and induced resistance. Smallholder farmers in much of Africa practice mixed cropping. Thus, a Push-Pull system will be developed modelled along the polycropping nature of these farming systems, for which repellent intercrop (Push) and attractive trap crop (Pull) components are required. Candidate repellent intercrops will be tested for their ability to repel FAW moths, and will include a range of African food legumes; while candidate attractive trap crops will be tested for their ability to attract the moths. Field sampling will be conducted to determine the key natural enemies that attack FAW and insects reared in the laboratory so that parasitoids emerging can be recorded. Field sampling of potential reservoir hosts (wild plants) will be conducted to determine their role in pest epidemiology and the possible ecosystem service they may provide by acting as habitat for natural enemies of the pest. To assess indirect defence, volatiles collected from infested plants will be tested in an olfactometer to determine if key predators and parasitoids prefer them. Volatiles from intercrops will be tested for attraction of natural enemies. For plants that have reduced feeding and growth rates of FAW larvae, secondary metabolites will be extracted by solvent washing and the collected extracts analysed by HPLC. Volatiles will be collected from plants that significantly repel or attract insects, or where a difference in moth oviposition preference is observed. Headspace samples of volatiles will be analysed by GC-EAG and GC-MS to identify bioactive compounds. Field trials will be conducted with crops with improved resistance to FAW grown with appropriate companion crops to support biological control by natural enemies. Co-design workshops will be held with participating farmers and trials will be held on their farms.

Who might benefit from this research?

This research will benefit smallholder farmers who require improved cropping systems that are resilient to attack from the invasive fall armyworm pest. The agricultural landscapes of SSA are dominated by family smallholder farms, where women provide the majority of agricultural labour but seldom own the land they farm. Women often lack some or all of the resources that are needed to grow enough food to ensure household food security - whether seeds, tools, fertilizers, knowledge or the power to make strategic decisions about the farm. In this region, grain is at the heart of the household economy, grown for both consumption and sale. But cereal production is constrained by insect pests, and the fall army worm invasion is a new threat. Getting enough to eat is a constant worry for too many households.

Society will benefit because the food system in developing countries is highly dependent on smallholder farmers who are typically responsible for over 85% of food production. Currently these food supply chains are highly vulnerable to crop losses to pests.


How might they benefit from this research?

Farmers will benefit from a range of options to reduce pest damage. These will be resistant crop varieties, crop varieties that attract natural enemies of pests, intercrops that repel pests and trap crops which attract them. All these will be combined in a Push-Pull mixed cropping system. Reduced losses to pest remove uncertainties relating to food security and income security.

As well as managing pests, our approach will include features already built into the Push-Pull companion cropping approach, namely:
- striga weed management through suppressive root exudates of intercrops
- provision of sources of forage for animals
- improvement of soil fertility with nitrogen fixing intercrops that also improve soil organic matter content
- climate smart features as the mixed cropping system is drought resilient

Health will be promoted because food and nutritional insecurity is the biggest risk factor for poor health in developing countries with approximately 50% of infant mortality caused by inadequate nutrition. Securing production will directly benefit subsistence farmers as well as reducing food costs in the food chain. The programme would reduce dependency on pesticides for crop protection thus reducing the health risks involved in pesticide application by hand with backpack sprayers. Social welfare will be promoted by giving smallholder farmers, particularly women, a wider range of options for pest management which will improve their welfare.