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Fall armyworm (Spodoptera frugiperda Smith), a serious pest of cereals from the Americas, has spread across sub-Saharan Africa and Asia since 2016, threatening the food security and incomes of millions of smallholder farmers. To measure the impact of S. frugiperda under different management approaches, we established on-farm trials across 12 landscapes (615−1,379 mm mean annual rainfall) in Malawi and Zambia during the 2019/2020 and 2020/2021 seasons. Here we present the results from our conventional tillage, monocrop maize, no pesticide treatment, which served to monitor the background S. frugiperda impact in the absence of control measures. Median plot-level S. frugiperda incidence ranged between 0.00 and 0.52 across landscapes. Considering severe leaf damage (Davis score ≥5), the proportion of affected plants varied between 0.00 and 0.30 at the plot scale, but only 3% of plots had ≥10% severely damaged plants. While incidence and damage severity varied substantially among sites and seasons, our models indicate that they were lower in high tree cover landscapes, in the late season scouting, and in the 2020/2021 season. Yield could not be predicted from S. frugiperda incidence or leaf damage. Our results suggest S. frugiperda impacts may have been overestimated at many sites across sub-Saharan Africa. S. frugiperda incidence and damage declined through the cropping season, indicating that natural mortality factors were limiting populations, and none of our plots were heavily impacted. Long-term S. frugiperda management should be based on Integrated Pest Management (IPM) principles, including minimising the use of chemical pesticides to protect natural enemies.

Invasive species pose a significant threat to biodiversity and agriculture world-wide. Natural enemies play an important part in controlling pest populations, yet we understand very little about the presence and prevalence of natural enemies during the early invasion stages. Microbial natural enemies of fall armyworm Spodoptera frugiperda are known in its native region, however, they have not yet been identified in Africa where fall armyworm has been an invasive crop pest since 2016. Larval samples were screened from Malawi, Rwanda, Kenya, Zambia, Sudan and Ghana for the presence of four different microbial natural enemies; two nucleopolyhedroviruses, Spodoptera frugiperda NPV (SfMNPV) and Spodoptera exempta NPV (SpexNPV); the fungal pathogen Metarhizium rileyi; and the bacterium Wolbachia. This study aimed to identify which microbial pathogens are present in invasive fall armyworm, and determine the geographical, meteorological and temporal variables that influence prevalence. Within 3 years of arrival, fall armyworm was exposed to all four microbial natural enemies. SfMNPV probably arrived with fall armyworm from the Americas, but this is the first putative evidence of host spillover from Spodoptera exempta (African armyworm) to fall armyworm for the endemic pathogen SpexNPV and for Wolbachia. It is also the first confirmed incidence of M. rileyi infecting fall armyworm in Africa. Natural enemies were localised, with variation being observed both nationally and temporally. The prevalence of SfMNPV (the most common natural enemy) was predominantly explained by variables associated with the weather; declining with increasing rainfall and increasing with temperature. However, virus prevalence also increased as the growing season progressed. The infection of an invasive species with a natural enemy from its native range and novel pathogens specific to its new range has important consequences for understanding the population ecology of invasive species and insect–pathogen interactions. Additionally, while it is widely known that temporal and geographic factors affect insect populations, this study reveals that these are important in understanding the distribution of microbial natural enemies associated with invasive pests during the early stages of invasion, and provide baseline data for future studies.

Fall armyworm (Spodoptera frugiperdaJ. E. Smith), a serious pest of maize and other cereals, recently invaded the Old World potentially threatening the food security and incomes of millions of smallholder farmers. Being able to assess the impacts of a pest on yields is fundamental to developing Integrated Pest Management (IPM) approaches. Hence, working with an early maturing, medium maturing and late maturing variety, we inoculated maize plants with 2ndinstarS. frugiperdalarvae at V5, V8, V12, VT and R1 growth stages. Different plants were inoculated 1-3 times and larvae were removed after 1 or 2 weeks to generate a wide range of leaf damage profiles. We scored plants for leaf damage at 3, 5 and 7 weeks after emergence (WAE) using the Davis scale, and at harvest plant height, ear damage and grain yield per plant were recorded. We used Structural Equation Models to assess the direct effects of leaf damage on yield and indirect effects via plant height. For the early and medium maturing varieties leaf damage at 3 and 5 WAE, respectively, had significant negative linear effects on grain yield. In the late maturing variety, leaf damage at 7 WAE had an indirect effect on yield through a significant negative linear effect on plant height. However, despite the controlled screenhouse conditions, in all three varieties leaf damage explained less than 3% of the variation in yield at the plant level. Overall, these results indicate thatS. frugiperdainduced leaf damage has a slight but detectable impact on yield at a specific plant developmental stage, and our models will contribute to the development of decision-support tools for IPM. However, given the low average yields obtained by smallholders in sub-Saharan Africa and the relatively low levels of FAW induced leaf damage recorded in most areas, IPM strategies should focus on interventions aimed at improving plant vigour (e.g. through integrated soil fertility management) and the role of natural enemies, as these are likely to result in greater yield gains at lower cost than alternatives.

Forecasting the spread of emerging pests is widely requested by pest management agencies in order to prioritise and target efforts. Two widely used approaches are statistical Species Distribution Models (SDMs) and CLIMEX, which uses ecophysiological parameters. Each have strengths and weaknesses. SDMs can incorporate almost any environmental condition and their accuracy can be formally evaluated to inform managers. However, accuracy is affected by data availability and can be limited for emerging pests, and SDMs usually predict year-round distributions, not seasonal outbreaks. CLIMEX can formally incorporate expert ecophysiological knowledge and predicts seasonal outbreaks. However, the methods for formal evaluation are limited and rarely applied. We argue that both approaches can be informative and complementary, but we need tools to integrate and evaluate their accuracy. Here we develop such an approach, and test it by forecasting the potential global range of the tomato pest Tuta absoluta.The accuracy of previously developed CLIMEX and new statistical SDMs were comparable on average, but the best statistical SDM techniques and environmental data substantially outperformed CLIMEX. The ensembled approach changes expectations of T. absoluta's spread. The pest's environmental tolerances and potential range in Africa, the Arabian Peninsula, Central Asia and Australia will be larger than previous estimates.We recommend that CLIMEX be considered one of a suite of SDM techniques and thus evaluated formally. CLIMEX and statistical SDMs should be compared and ensembled if possible. We provide code that can be used to do so when employing the biomod suite of SDM techniques. © 2021 The Authors. Pest Management Science published by John WileySons Ltd on behalf of Society of Chemical Industry.

The major plant pest fall armyworm (FAW),Spodoptera frugiperda, is native to the Americas and has colonized African and Asian countries in the Eastern hemisphere since 2016, causing severe damage to multiple agricultural crop species. However, the genetic origin of these invasive populations require more in-depth exploration. We analyzed genetic variation across FAW genomes of 153 newly sequenced individuals from Eastern hemisphere and 127 individuals mostly originating from the Americas. The global genetic structure of FAW shows that the FAW in American has experienced deep differentiation, largely consistent with the Z-chromosomalTpihaplotypes commonly used to differentiate “corn-strain” and “rice-strain” populations. Results indicate that the invasive Eastern hemisphere populations are different from the American ones and have relatively homogeneous population structure, consistent with the common origin and recent spreading from Africa to Asia. Our analyses suggest that north-and central American “corn-strain” FAW are the most likely sources of the invasion into the Eastern hemisphere. Furthermore, evidence based on genomic, transcriptomic and mitochondrial haplotype network analysis suggest that there has been an earlier independent introduction of FAW into Africa that introgressed into the recent invasive population.

Insect pests are a major challenge to smallholder crop production in sub-Saharan Africa, where access to synthetic pesticides, which are linked to environmental and health risks, is often limited. Biological control interventions could offer a sustainable solution, yet an understanding of their effectiveness is lacking. We conducted a meta-analysis of 5 commonly-used biocontrol interventions to quantify i) the magnitude of their effects when compared with no control and with synthetic pesticides, and ii) how effectiveness is determined by landscape composition. Overall, compared to no control, biocontrol interventions reduced pest abundance by 63%, crop damage by over 50%, and increased crop yield by over 60%. Compared to synthetic pesticides, biocontrol produced comparable yields, and natural enemy abundance was 43% greater. Our results suggest that biocontrol represents an effective intervention for farmers who do not have access to pesticides, while it can maintain yields without associated negative pesticide effects. However, the potential for biocontrol to be affected by landscape composition is a critical knowledge gap in sub-Saharan Africa.

Research studies were conducted to screen 110 cowpea genotypes against Callosobruchus maculatus commonly known as the cowpea weevil, under the no-choice infestation condition. Out of all the genotypes screened, BBBT1-11 outperformed all the genotypes across all parameters investigated. BBBT1-11 recorded 13.01 no. of eggs/100 seeds compared to MS1-8-2-6-9-1 with 128.67 eggs/100 seeds. The adult emergence on BBBT1-11 was at 12.72% compared to the highest LTBT1-5 at 88.11%. The lowest growth index of 0.42 and frass of 0.23g was recorded on BBBT1-11. BBBT1-11 could be further assessed for the possible presence of biochemical substances, which could explain the observed differences among the genotypes in their reaction to C. maculatus. Besides, BBBT1-11 can also be incorporated into the breeding program with the target of breeding cowpea varieties that are tolerant to pest infestation.

Research studies aimed at screening cowpea genotypes against Aphis craccivora K. commonly known as black aphids, under the no-choice infestation condition, were conducted in the greenhouse at Natural Resource Development College (NRDC), Lusaka, Zambia in 2021. The main objective was to discern the cowpea genotype that is resistant to Aphis craccivora K that would aid the reduction of yield losses encountered in cowpea production. The most resistant genotype BBBT1-11 across all parameters investigated recorded an average aphid score of 1.0, compared to LT11-3-3-12 which recorded the highest score of 7.0. The aphid population build-up of BBBT1-11 was 1.0 compared to the highest recorded by LT11-5-1-1-4 at 3.54. The highest plant vigour of 3.0 was recorded by BBBT1-11, BB10-4-3-2, and LT11-5-1-1-4, and the lowest was recorded by Sanzi (1.2). BBBT1-11 recorded a survival percentage of 100% at 21DAI compared to the lowest recorded by TVu 2027 (20%). Mutant line BBBT1-11 emerged as a resistant genotype across all parameters tested including weight of seeds/plant and number of seeds/plant. BBBT1-11 could further be assessed for the possible presence of biochemicals and traits, that could explain the basis of the observed differences among the genotypes in their reaction to Aphis craccivora K. Besides, BBBT1-11 can also be incorporated in the breeding program with the target of breeding cowpea varieties that are resistant to aphid infestation to address the yield losses experienced in cowpea production as a result of A. craccivora K.