Biopesticides for Africa: A model system

African agriculture is impacted by a range of stresses leading to losses in yield, of which insect crop pests are a major problem. It has been estimated that agricultural crop pests account for around a 30% loss of crops grown globally. Conventional chemical pesticides are highly effective at protecting such crops, but are generally expensive and in Tanzania, for example, more than 70% of farmers cannot afford them. It is a similar story throughout most of sub-Saharan Africa. In addition to the problems with cost, those farmers who can afford them risk exposing themselves to harmful chemicals due to a lack of appropriate safety gear. Moreover, many chemical pesticides harm beneficial insects such as pollinators, livestock and the wider environment; in Europe this has resulted in a drastic reduction in the number of chemical products allowed in crop protection over the last two decades.

Both globally and across Africa in particular, there is a pressing need to develop cheaper, environment-friendly alternatives to chemical pesticides, and this is the focus of our project. Biological pesticides used to protect agricultural crops are derived from plants and microorganisms, such as fungi, bacteria, and viruses. They are often much cheaper to develop than new chemicals and, currently, global sales of biopesticides are estimated to be worth $2.3 billion, around 5% of the overall pesticides market and growing at around 16% per annum.

The long-term goal of our proposed study is to develop a novel, cheap, effective and locally-produced biopesticide in Tanzania (known as SpexNPV) to combat the one of the most infamous insect pests in sub-Saharan Africa. This pest is the caterpillar stage of the African armyworm moth (Spodoptera exempta). The product will be derived from a naturally-occurring virus, which is ever-present in natural populations of the armyworm in small amounts. Whilst our proposal necessarily addresses issues that are specific to the armyworm-SpexNPV system, this can better be viewed as a model system for understanding generic technical and production issues associated with the mass-production, mass-application and formulation of novel biopesticides, especially in Africa.

The overall objective of the proposed study is to use a specific host-biopesticide system (African armyworm-SpexNPV baculovirus) as a model for exploring some of the key issues associated with developing and deploying a new biopesticide in Africa. We will do so by better understanding the process of developing and applying the biopesticide. Specifically, we will test to see what impact application of the biopesticide has upon the target insect (e.g. will it develop resistance to the pesticide over time?), its gut microbial community (e.g. does this protect or harm its host?) and the effectiveness of the biopesticide itself (does it evolve undesirable traits over time?), and the potential to utilise this knowledge to develop novel biocontrol strategies (e.g. can we design novel combinations of viruses and bacteria to make the biopesticide more effective and cheaper?).

Food security in sub-Saharan Africa is impacted by a range of stresses leading to losses in crop yield, of which insect pests are a major contributor. Whilst chemical pesticides are highly effective at protecting such crops, they are generally prohibitively expensive to the smallholder. The objective of this study is to use a specific host-biopesticide system (Spodoptera exempta-SpexNPV baculovirus) as a model for exploring the key issues associated with developing and deploying a new biopesticide in Africa.

Firstly, we will establish whether continual 'field production' of biopesticide will lead to selection for undesirable biopesticide traits. Specifically, whether the genetic and phenotypic profile of SpexNPV changes following host selection. This will be tested using both field trials in Africa and laboratory bioassays in the UK, in which the genetic and phenotypic traits of the virus will be quantified pre- and post-selection. Secondly, we will test whether mass-inundation of biopesticide is likely to select for a more resistant host population. Specifically, will controlling the armyworm pest population with SpexNPV inadvertently select for resistant, or generally more vigorous, insects? And thirdly, does the gut microbiota of the host influence susceptibility to the biopesticide and can this be manipulated to improve biopesticide efficacy? For example, are there resident microbes that influence S. exempta susceptibility to viral disease, or can we combine SpexNPV with other microbes to make armyworms more susceptible to infection? Laboratory trials will be undertaken testing gut microbiota faecal transplants between susceptible and resistant hosts to compare host genetic and microbiome effects, as well as exploring the possibility that specific gut bacteria modulate host susceptibility to baculoviruses. Ultimately, this project will answer key questions regarding the development and application of field-based, mass-production techniques for biopesticides.

A major contributor to poverty in sub-Saharan Africa is the inability to produce sufficient food for a growing population, due partly to crop losses caused by insect pests. Most smallholder farmers cannot access expensive imported chemical pesticides, and where these are used they risk having damaging effects on the health of humans, beneficial insects, livestock and the wider environment. Biopesticides derived from microbial pathogens of insects could provide a lower-cost, environment-friendly solution for the control of crop pests by these farmers. The proposed study will address key issues in the production and use of biopesticides in Africa, and could have significant long-term impact.

The main beneficiaries of this research are likely to be the following:

BIOPESTICIDES INDUSTRY: Around a half of current chemical pesticides used in Europe will soon be banned due to environmental concerns. As a result, there is renewed interest in biopesticides in the EU and indeed globally. The research proposed here focusses on the interaction between the African armyworm and SpexNPV, a baculovirus we are developing as a biopesticide in Africa in collaboration with a Tanzanian SME, Crop Bioscience Solutions Ltd., who will be an immediate beneficiary of this research. Outputs from the proposed activities will feed directly into this biopesticides research programme by providing new insights into the long-term consequences of biopesticide field-production and mass-application. By understanding these challenges and opportunities, we hope to develop 'smarter' strategies for their use. For example, we envisage it might be possible to combine the SpexNPV-biopesticide with bacteria to enhance its efficacy against the pest, taking advantage of a previously identified interaction between armyworms, SpexNPV and a bacterial endosymbiont called Wolbachia: armyworms carrying Wolbachia are up to 14 times more susceptible to SpexNPV than those that are not. If similar interactions are observed with other bacteria, then this could be developed as a novel biopesticide 'combination' formulation for the control of African armyworms. And if similar interactions occur between other pest-virus-bacteria interactions then other novel biopesticides may also be developed.

FOOD PRODUCERS: Insect crop pests pose a major threat to global food security. The proposed research will contribute to our understanding of insect pest outbreaks and their control using biological biopesticides. In particular, it will provide us with a greater understanding of the factors that might limit the success of biopesticides, such as the evolution of host resistance, the effects of microbial symbionts, and virus virulence effects.

AGRICULTURAL COMMUNITIES IN AFRICA: Our previous research has already generated some important new findings (e.g. genetic and phenotypic diversity of the baculovirus and its epidemiology in natural armyworm outbreaks), and has resulted in the building of a biopesticide production facility in Tanzania, managed by project collaborator Crop Bioscience Solutions Ltd. Throughout this process, we have built capacity in biopesticide production and application via engagement with government, private sector and universities. In December 2013, PI Wilson met with the Vice-President of Zambia to advise on the control of African armyworm following a major food crisis caused by the pest, demonstrating that this research is likely to have impact at the highest levels in Africa. The proposed project would maintain these existing channels of communication and establish new ones, especially with the academic community in Africa via new links with the Nelson Mandela African Institution for Science and Technology (NM-AIST). Our impact plan includes a 'biopesticides' workshop specifically targeted at young scientists in Tanzania, in the hope of inspiring the next generation of biopesticide innovators in the region.