Kenneth Wilson

The fall armyworm (Spodoptera frugiperda) is an invasive pest of global concern, posing a significant threat to food security. It can be divided into two biotypes: the rice strain (RS) and the corn strain (CS). These two biotypes are nearly indistinguishable morphologically but differ significantly in host adaptability. The two biotypes can hybridize, but the efficiency of their hybridization has not been conclusively determined. Our research has found that the two biotypes of fall armyworm exhibit significant differences in weight gain when feeding on different host plants and artificial diets. The rice strain has a broader diet range, showing notably stronger adaptability to rice and ryegrass compared to the corn strain, suggesting that the rice strain may possess more robust detoxification metabolism. Under laboratory conditions, the two biotypes can hybridize effectively, and their offspring exhibit certain hybrid advantages. The host adaptability traits of the rice strain are dominantly inherited. Our findings provide an important foundation for understanding the biological basis of host adaptability in the rice strain of fall armyworm.

Understanding the role of nutrients in microbial population dynamics relies on a sound appreciation of their nutritional environment and how this may vary in different habitats. For microbial pathogens and commensals, this can be especially challenging because the microbe may share nutritional resources with its host. Here we design a series of 20 synthetic cell‐free haemolymphs ( nutribloods ) that mimic haemolymph nutrient profiles of caterpillars fed on one of 20 chemically defined diets that vary in their protein: carbohydrate (P:C) ratio and caloric density. Using these, we are able to simulate the range of nutritional conditions that insect blood pathogens might face, providing a model system for understanding the role of nutrition in microbial growth. We tested this using the entomopathogen, Xenorhabdus nematophila , a Gram‐negative extracellular bacterium of insect hosts. This revealed that whilst bacterial fitness peaked in nutriblood nutrient space that was high in carbohydrates and low in proteins, levels of amino acids in the nutribloods also appear to be an important driving force for bacterial growth. Using synthetic haemolymphs that had average levels of all nutrients other than carbohydrate, protein or amino acids, we also established that bacterial growth is generally enhanced by carbohydrates and amino acids but reduced by proteins. Here, we have established a tractable model system for examining the role that nutrition plays in the growth of an entomopathogenic bacterium. In future work, this model host–pathogen system can be used to test a range of nutritionally driven processes, including competition during co‐infection and interactions with the host microbiome, as well as comparative studies of other entomopathogens.

Nutrition often shapes the outcome of host–parasite interactions, however understanding the mechanisms by which this occurs is often confounded by the intimate nature of the association and by the fact that the host and parasite may compete for the same limiting nutrients. One way of disentangling this interaction is to combine in vivo and in vitro approaches. Here, we explore the role of host nutrition in determining the outcome of infections using a model insect‐bacterium system: the cotton leafworm Spodoptera littoralis and the blood‐borne bacterium Xenorhabdus nematophila. Spodoptera littoralis larvae were reared on one of a series of 20 chemically‐defined diets ranging in their protein: carbohydrate (P:C) ratio and caloric density. They were then challenged with either a fixed dose of X. nematophila cells (live or dead) or were sham‐injected. Survivorship of larvae challenged with live bacterial cells was strongly dependent on the protein levels of the diet, with mortality being highest on low‐protein diets. This trend was reflected in the bacterial growth rate in vivo, which peaked in larvae fed low‐protein diets. To determine whether in vivo bacterial growth rates were driven by the direct effects of blood nutrients or by the indirect effects of the host immune response, we used 20 synthetic haemolymphs (‘nutribloods’) that mimicked the nutritional content of host blood. In vitro bacterial growth rate was negatively impacted by the protein content of the nutribloods, replicating the patterns seen in vivo and suggesting that nutrient availability and not host immunity was driving the interaction. By comparing standardized bacterial growth rates in vivo and in vitro, we conclude that the outcome of this host–parasite interaction is largely driven by the ‘bottom‐up’ effects of nutrients on bacterial growth, rather than by the ‘top‐down’ effects of nutrients on host‐mediated immune responses. The outcome of host–parasite interactions is typically assumed to be strongly determined by the host immune response. The direct effects of nutrition have been underexplored and may have broad consequences for host–parasite interactions across taxa.

Summary: The interactions among plant viruses, insect vectors, and host plants have been well studied; however, the roles of insect viruses in this system have largely been neglected. We investigated the effects of MpnDV infection on aphid and PVY transmission using bioassays, RNA interference (RNAi), and GC‐MS methods and green peach aphid (Myzus persicae (Sulzer)), potato virus Y (PVY), and densovirus (Myzus persicae nicotianae densovirus, MpnDV) as model systems. MpnDV increased the activities of its host, promoting population dispersal and leading to significant proliferation in tobacco plants by significantly enhancing the titer of the sesquiterpene (E)‐β‐farnesene (EβF) via up‐regulation of expression levels of the MpFPPS1 gene. The proliferation and dispersal of MpnDV‐positive individuals were faster than that of MpnDV‐negative individuals in PVY‐infected tobacco plants, which promoted the transmission of PVY. These results combined showed that an insect virus may facilitate the transmission of a plant virus by enhancing the locomotor activity and population proliferation of insect vectors. These findings provide novel opportunities for controlling insect vectors and plant viruses, which can be used in the development of novel management strategies.

Nutrition often shapes the outcome of host-parasite interactions, however understanding the mechanisms by which this occurs is confounded by the intimate nature of the association and by the fact that the host and parasite may compete for the same limiting nutrients. One way of disentangling this interaction is to combine in vivo and in vitro approaches. Here, we explore the role of host nutrition in determining the outcome of infections using a model insect-bacterium system: the cotton leafworm Spodoptera littoralis and the blood-borne bacterium Xenorhabdus nematophila . Spodoptera littoralis larvae were reared on one of a series of 20 chemically-defined diets ranging in their protein: carbohydrate (P:C) ratio and caloric density. They were then challenged with either a fixed dose of X. nematophila cells (live or dead) or were sham-injected. Survivorship of larvae challenged with live bacterial cells was strongly dependent on the protein levels of the diet, with mortality being highest on low-protein diets. This trend was reflected in the bacterial growth rate in vivo , which peaked in larvae fed low-protein diets. To determine whether in vivo bacterial growth rates were driven by blood nutrients, rather than an enhanced host immune response, we generated 20 synthetic haemolymphs (‘nutribloods’) that mimicked the nutritional content of host blood. Bacterial growth rate in the nutribloods was also negatively impacted by their protein content suggesting that nutrient availability and not host immunity was driving the interaction. By comparing standardized bacterial growth rates in vivo and in vitro , we conclude that the outcome of this host-parasite interaction is largely driven by ‘bottom-up’ effects of nutrients on bacterial growth, rather than by ‘top-down’ effects of nutrients on host-mediated immune responses. The outcome of host-parasite interactions is typically assumed to be strongly determined by the host immune response. The direct effects of nutrition have been underexplored and may have broad consequences for host-parasite interactions across taxa.

Understanding the role of nutrients in microbial population dynamics relies on a sound appreciation of their nutritional environment and how this may vary in different habitats. For microbial pathogens and commensals, this can be especially challenging because the microbe may share nutritional resources with its host. Here we design a series of 20 synthetic haemolymphs ( nutribloods ) that mimic haemolymph nutrient profiles of caterpillars fed on one of 20 chemically-defined diets, that vary in their protein:carbohydrate (P:C) ratio and caloric density. Using these, we are able to simulate the range of nutritional conditions that insect blood pathogens might face, providing a model system for understanding the role of nutrition in microbial growth. We tested this using the entomopathogen, Xenorhabdus nematophila , a gram-positive extracellular bacterium of insect hosts. This revealed that whilst bacterial fitness peaked in nutriblood nutrient space that was high in carbohydrates and low in proteins, levels of amino acids in the nutribloods also appear to be an important driving force for bacterial growth. Using synthetic haemolymphs that had average levels of all nutrients other than carbohydrate, protein or amino acids, we also established that bacterial growth is generally enhanced by carbohydrate and amino acids but reduced by proteins. Here, we have established a tractable model system for examining the role that nutrition plays in the growth of an entomopathogenic bacterium. In future work, this model host-pathogen system can be used to test a range of nutritionally-driven processes, including competition during co-infection and interactions with the host microbiome, as well as comparative studies of other entomopathogens.

Insects are the most diverse animal group on the planet. Their success is reflected by the diversity of habitats in which they live. However, these habitats have undergone great changes in recent decades; understanding how these changes affect insect health and fitness is an important challenge for insect conservation. In this Review, we focus on the research that links the nutritional environment with infection and immune status in insects. We first discuss the research from the field of nutritional immunology, and we then investigate how factors such as intracellular and extracellular symbionts, sociality and transgenerational effects may interact with the connection between nutrition and immunity. We show that the interactions between nutrition and resistance can be highly specific to insect species and/or infection type – this is almost certainly due to the diversity of insect social interactions and life cycles, and the varied environments in which insects live. Hence, these connections cannot be easily generalised across insects. We finally suggest that other environmental aspects – such as the use of agrochemicals and climatic factors – might also influence the interaction between nutrition and resistance, and highlight how research on these is essential.

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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.