Predicting potential global and future distributions of the African armyworm (Spodoptera exempta) using Species Distribution Models

Invasive species have historically been a problem derived from global trade and transport. To aid in the control and management of these species, Species Distribution Models (SDMs) have been used to help predict possible areas of expansion. Our focal organism, the African Armyworm (AAW), has historically been known as an important pest species in Africa, occurring at high larval densities and causing outbreaks that can cause enormous economic damage to staple crops. The goal of this study is to map the AAW’s present and potential distribution in three future scenarios for the region, and the potential global distribution if the species were to invade other territories, using 40 years of data on more than 700 larval outbreak reports from Kenya and Tanzania. The present distribution in East Africa coincides with its previously known distribution, as well as other areas of grassland and cropland, which are the host plants for this species. The different future climatic scenarios show broadly similar potential distributions in East Africa to the present day. The predicted global distribution shows areas where the AAW has already been reported, but also shows many potential areas in the Americas where, if transported, environmental conditions are suitable for AAW to thrive and where it could become an invasive species

The use of indigenous ecological resources for pest control in Africa

Reducing the losses from crop pests will help to increase food availability and boost economic growth in sub-Saharan Africa (SSA). However, the existing crop protection paradigm that relies on synthetic agrochemical pesticides has had only a marginal impact on the productivity of many poor smallholder farmers who constitute a major segment of agriculture in SSA. This is primarily because many of them are not able to afford or access these imported chemicals. A solution to this crop protection problem may be to harness biological resources that are locally available, such as endemic insect natural enemies and indigenous pesticidal plant materials. Two specific examples of this already under development in Africa are the use of the pesticidal plant, Tephrosia vogelii , and the harvesting of the endemic insect baculovirus, Spodoptera exempta nucleopolyhedrovirus (SpexNPV). Both of these can be produced locally and have shown promise in trials as inexpensive and effective tools for pest control in Africa and their use is currently being scaled up and evaluated by African networks of researchers. A focus on these systems illustrates the potential for using locally-available natural resources for improved crop protection in Africa. The consideration of these pesticidal plants and insect natural enemies in the wider context of natural capital that provide valuable ecosystem services (including pest control), will facilitate greater recognition of their true economic and societal worth. While both of these model systems show promise, there are also very significant challenges to be overcome in developing production, supply and marketing systems that are economically viable and sustainable. The regulatory environment must also evolve to accommodate and facilitate the registration of new products and the establishment of appropriate supply chains that share the benefits of these resources equitably with the local communities from which they are harvested

Wolbachia in a major African crop pest increases susceptibility to viral disease rather than protects

Wolbachia are common vertically transmitted endosymbiotic bacteria found in <similar to 70% of insect species. They have generated considerable recent interest due to the capacity of some strains to protect their insect hosts against viruses and the potential for this to reduce vector competence of a range of human diseases, including dengue. In contrast, here we provide data from field populations of a major crop pest, African armyworm (Spodoptera exempta), which show that the prevalence and intensity of infection with a nucleopolydrovirus (SpexNPV) is positively associated with infection with three strains of Wolbachia. We also use laboratory bioassays to demonstrate that infection with one of these strains, a male-killer, increases host mortality due to SpexNPV by 614 similar to times. These findings suggest that rather than protecting their lepidopteran host from viral infection, Wolbachia instead make them more susceptible. This finding potentially has implications for the biological control of other insect crop pests

Evaluation of Spodoptera exempta nucleopolyhedrovirus (SpexNPV) for the field control of African armyworm (Spodoptera exempta) in Tanzania

The African armyworm Spodoptera exempta is a major episodic migratory crop pest over much of Eastern and Southern Africa. Control of this pest has been reliant on the use of synthetic chemical insecticides. However, this approach fails to protect poor farmers and is becoming unacceptable for environmental and cost reasons. A programme of field trials was conducted in Tanzania to evaluate the endemic baculovirus, the S. exempta nucleopolyhedrovirus (SpexNPV), as an alternative control. Field trials demonstrated that both ground and aerial application of SpexNPV to armyworm outbreaks on pasture can initiate outbreaks of NPV disease and population collapses. The SpexNPV was effective when applied at 1×1012 occlusion bodies (OB) per hectare if applied to outbreaks early, when larvae are in I–III instar—mass mortalities appear 3–10 days post treatment. The data from these trials indicate that SpexNPV can have a potential role as a substitute for chemical insecticides in strategic armyworm management programmes