Comparing, evaluating and combining statistical species distribution models and CLIMEX to forecast the distributions of emerging crop pests.

This is the final version. Available from Wiley via the DOI in this record. The data that support the findings of this study are openly available in Github at https://github.com/Fabiogeography/biomod_climex.BACKGROUND: 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. RESULTS: 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. CONCLUSION: 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.Biotechnology & Biological Sciences Research Council (BBSRC)European Regional Development Fund (ERDF)CAB

Microsatellites reveal that genetic mixing commonly occurs between invasive fall armyworm populations in Africa

Abstract: Understanding the population structure and movements of the invasive fall armyworm (FAW, Spodoptera frugiperda) is important as it can help mitigate crop damage, and highlight areas at risk of outbreaks or evolving insecticide resistance. Determining population structure in invasive FAW has been a challenge due to genetic mutations affecting the markers traditionally used for strain and haplotype identification; mitochondrial cytochrome oxidase I (COIB) and the Z-chromosome-linked Triosephosphate isomerase (Tpi). Here, we compare the results from COIB and Tpi markers with highly variable repeat regions (microsatellites) to improve our understanding of FAW population structure in Africa. There was very limited genetic diversity using the COIB marker, whereas using the TpiI4 marker there was greater diversity that showed very little evidence of genetic structuring between FAW populations across Africa. There was greater genetic diversity identified using microsatellites, and this revealed a largely panmictic population of FAW alongside some evidence of genetic structuring between countries. It is hypothesised here that FAW are using long-distance flight and prevailing winds to frequently move throughout Africa leading to population mixing. These approaches combined provide important evidence that genetic mixing between invasive FAW populations may be more common than previously reported

Biological control interventions reduce pest abundance and crop damage while maintaining natural enemies in sub-Saharan Africa: a meta-analysis

Insect pests are a major challenge to smallholder crop production in sub-Saharan Africa (SSA), 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 used a meta-analysis approach to investigate the effectiveness of commonly used biocontrol interventions and botanical pesticides on pest abundance (PA), crop damage (CD), crop yield (Y) and natural enemy abundance (NEA) when compared with controls with no biocontrol and with synthetic pesticides. We also evaluated whether the magnitude of biocontrol effectiveness was affected by type of biocontrol intervention, crop type, pest taxon, farm type and landscape configuration. Overall, from 99 studies on 31 crops, we found that compared to no biocontrol, biocontrol interventions reduced PA by 63%, CD by over 50% and increased Y by over 60%. Compared to synthetic pesticides, biocontrol resulted in comparable PA and Y, while NEA was 43% greater. Our results also highlighted that the potential for biocontrol to be modulated by landscape configuration is a critical knowledge gap in SSA. We show that biocontrol represents an effective tool for smallholder farmers, which can maintain yields without associated negative pesticide effects. Furthermore, the evidence presented here advocates strongly for including biocontrol practices in national and regional agricultural policies

The distribution of covert microbial natural enemies of a globally invasive crop pest, fall armyworm, in Africa: enemy-release and spillover events

1. Invasive species pose a significant threat to biodiversity and agriculture worldwide. 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. 2. 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. 3. Within three 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. 4. 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. 5. 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, whilst 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

Genetic structure and insecticide resistance characteristics of fall armyworm populations invading China

The rapid wide-scale spread of fall armyworm (Spodoptera frugiperda) has caused serious crop losses34 globally. However, differences in the genetic background of subpopulations and the mechanisms of rapid adaptation behind the invasion are still not well understood. Here we report the assembly of a 390.38-M chromosome-level genome of fall armyworm using Pacific Bioscience (PacBio) and Hi-C sequencing technologies with scaffold N50 of 12.7 M consisting of 22260 annotated protein-coding genes. Genome-wide resequencing of 103 samples from 16 provinces in China revealed that the fall armyworm population comprises a complex inter-strain hybrid, mainly with the corn-strain genetic background and less of the rice-strain, which highlights the inaccuracy of strain identification using mitochondrial or Triosephosphate isomerase (Tpi) genes. Analysis of genes related to pesticide- and Bt-resistance showed that the risk of fall armyworm developing resistance to conventional pesticides is very high. Laboratory bioassay results showed that insects invading China carry resistance to organophosphate and pyrethroid pesticides, but are sensitive to genetically modified maize expressing Bacillus thuringiensis (Bt) toxins Cry1Ab in field experiments. Additionally, two mitochondrial fragments are inserted into the nuclear genome, and the insertion event occurred after the differentiation of the two strains. This study represents a valuable advance toward improving management strategies for fall armyworm

Understanding the impact of fall armyworm (Spodoptera frugiperda J. E. Smith) leaf damage on maize yields.

Fall armyworm (Spodoptera frugiperda J. 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 2nd instar S. frugiperda larvae at V5, V8, V12, VT and R1 growth stages to investigate the effects of FAW induced damage on yield. Different plants were inoculated 0-3 times and larvae were removed after 1 or 2 weeks to generate a wide range of damage profiles. We scored plants for leaf damage at 3, 5 and 7 weeks after emergence (WAE) using the 9 point Davis scale. While at harvest we assessed ear damage (1-9 scale), and recorded plant height and grain yield per plant. 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 that S. frugiperda induced 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 a focus on FAW control

Factors influencing the occurrence of fall armyworm parasitoids in Zambia

Invasive alien species have environmental, economic and social impacts, disproportionally threatening livelihood and food security of smallholder farmers in low- and medium-income countries. Fall armyworm (FAW) (Spodoptera frugiperda), an invasive insect pest from the Americas, causes considerable losses on maize to smallholder farmers in Africa since 2016. The increased use of pesticides to control FAW in Africa raises concerns for health and environmental risks resulting in a growing interest in research on biological control options for smallholder farmers. In order to evaluate the occurrence of local natural enemies attacking FAW, we collected on a weekly basis FAW eggs and larvae during a maize crop cycle in the rainy season of 2018–2019 at four locations in the Lusaka and Central provinces in Zambia. A total of 4373 larvae and 162 egg masses were collected. For each location and date of collection, crop stage, the number of plants checked and amount of damage were recorded to analyse which factors best explain the occurrence of the natural enemy species on maize. Overall parasitism rates from local natural enemies at each location varied between 8.45% and 33.11%. We identified 12 different egg-larval, larval and larval-pupal parasitoid species. Location, maize growth stage, pest density and larval stage significantly affected parasitoid species occurrence. Our findings indicate that there is potential for increasing local populations of natural enemies of FAW through conservation biological control programmes and develop safe and practical control methods for smallholder farmers.</p

Updated phylogenetic and systematics of the Acrapex albivena Hampson, 1910 and A. stygiata (Hampson, 1910) species groups (Lepidoptera, Noctuidae, Noctuinae, Apameini, Sesamiina), with the description of nine new species from the Afrotropics

International audienceThe genus Acrapex Hampson, 1891 (Lepidoptera, Noctuidae, Noctuinae, Apameini, Sesamiina) constitutes a speciose group of noctuid stemborers mostly distributed in the Afrotropics. In this study nine new Acrapex species are described: Acrapex abyssinica n. sp., Acrapex dabaga n. sp., Acrapex jansei n. sp., Acrapex kifanya n. sp., Acrapex lusinga n. sp., Acrapex ngwenya n. sp., Acrapex njombea n. sp., Acrapex vetiveria n. sp. and Acrapex zima n. sp. All species are assigned to the A. albivena group with the exception of A. lusinga which is assigned to the A. stygiata group. We also provide supplemental descriptions for two previously described species of the A. albivena group, A. punctosa Berio, 1973 and A. sysciodes Berio, 1973, and for one species belonging to the A. stygiata group: A. brunneella Le Ru, 2014. Host plants of three species are recorded; A. brunneella and Acrapex jansei were reared on Cymbopogon pospischilii (K.Schum.) C.E.Hubb and A. vetiveria on Chrysopogon zizanioides (L.). We also conducted molecular phylogenetic analyses (using both Bayesian inference and maximum likelihood) on a multi-marker (four mitochondrial and two nuclear genes) molecular dataset encompassing 138 specimens (including 98 specimens from the A. albivena group and 23 specimens from the A. stygiata group) from 48 stemborer species. The results of the corresponding analyses support the monophyly of the two groups of interest and the species status of all newly described taxa, except for A. lusinga that was not sequenced. The phylogenetic analyses also unravel several evolutionary lineages whose precise status is pending because their DNA was extracted from larval stages.Actualisation des connaissances de la phylogénie et de la systématique des groupes d’espèces Acrapex albivena Hampson, 1910 et A. stygiata (Hampson, 1910) (Lepidoptera, Noctuidae, Noctuinae, Apameini, Sesamiina), avec la description de neuf nouvelles espèces de la région Afrotropicale. Le genre Acrapex Hampson, 1891 (Lepidoptera, Noctuidae, Noctuinae, Apameini, Sesamiina) est un groupe diversifié de noctuelles foreuses, majoritairement distribué dans la région Afrotropicale. Dans cette étude neuf espèces nouvelles sont décrites : Acrapex abyssinica n. sp., Acrapex dabaga n. sp., Acrapex jansei n. sp., Acrapex kifanya n. sp., A. lusinga n. sp., Acrapex ngwenya n. sp., Acrapex njombea n. sp., Acrapex vetiveria n. sp. et Acrapex zima n. sp. Toutes ces espèces sont assignées au groupe d’espèce A. albivena à l’exception d’A. lusinga qui est assignée au groupe d’espèce A. stygiata. Nous fournissons également des descriptions supplémentaires pour deux espèces, A. punctosa Berio, 1973 et A. sysciodes, Berio 1973, précedemment décrites dans le groupe A. albivena ainsi que pour A. brunneella Le Ru, 2014, une espèce qui appartient au groupe A. stygiata. Les plantes-hôtes de trois espèces sont répertoriées ; Acrapex brunneella et A. jansei ont été élevées sur Cymbopogon pospischilii (K. Schum.) C. E. Hubb et A. vetiveria sur Chrysopogon zizanioides (L.). Nous avons également réalisé des analyses de reconstruction phylogénétique (utilisant à la fois l’inférence Bayésienne et le maximum de vraisemblance) sur un jeu de données moléculaires multi-marqueurs (quatre gènes mitochondriaux et deux gènes nucléaires) comprenant 138 specimens (incluant 98 specimens du groupe A. albivena et 23 specimens du groupe A. stygiata) de 48 espèces de foreurs. Les résultats de ces analyses soutiennent à la fois l’hypothèse de monophylie des deux groupes d’intérêt et le statut d’espèces des taxa nouvellement décris, à l’exception d’A. lusinga qui n’a pas été séquencé. Les analyses phylogénétiques révèlent également l’existence de plusieurs lignées évolutives distinctes dont le statut reste à définir car leur ADN a été extrait de stades larvaire