Enhanced toxicity of entomopathogenic fungi Beauveria bassiana with bacteria expressing immune suppressive dsRNA in a leaf beetle

Perilipin1 inhibits Nosema bombycis proliferation by promoting Domeless- and Hop-mediated JAK-STAT pathway activation in Bombyx mori

Lipid droplets (LDs) are dynamic organelles that participate in the regulation of lipid metabolism and cellular homeostasis inside of cells. LD-associated proteins, also known as perilipins (PLINs), are a family of proteins found on the surface of LDs that regulate lipid metabolism, immunity, and other functions. In silkworms, pébrine disease caused by infection by the microsporidian Nosema bombycis (Nb) is a severe threat to the sericultural industry. Although we found that Nb relies on lipids from silkworms to facilitate its proliferation, the relationship between PLINs and Nb proliferation remains unknown. Here, we found Nb infection caused the accumulation of LDs in the fat bodies of silkworm larvae. The characterized perilipin1 gene (plin1) promotes the accumulation of intracellular LDs and is involved in Nb proliferation. plin1 is similar to perilipin1 in humans and is conserved in all insects. The expression of plin1 was mostly enriched in the fat body rather than in other tissues. Knockdown of plin1 enhanced Nb proliferation, whereas overexpression of plin1 inhibited its proliferation. Furthermore, we confirmed that plin1 increased the expression of the Domeless and Hop in the JAK-STAT immune pathway and inhibited Nb proliferation. Taken together, our current findings demonstrate that plin1 inhibits Nb proliferation by promoting the JAK-STAT pathway through increased expression of Domeless and Hop. This study provides new insights into the complicated connections among microsporidia pathogens, LD surface proteins, and insect immunity.IMPORTANCELipid droplets (LDs) are lipid storage sites in cells and are present in almost all animals. Many studies have found that LDs may play a role in host resistance to pathogens and are closely related to innate immunity. The present study found that a surface protein of insect lipid droplets could not only regulate the morphological changes of lipid droplets but also inhibit the proliferation of a microsporidian pathogen Nosema bombycis (Nb) by activating the JAK-STAT signaling pathway. This is the first discovery of the relationship between microsporidian pathogen and insect lipid surface protein perilipin and insect immunity.

Entomopathogenic fungi in crops protection with an emphasis on bioactive metabolites and biological activities

Plant pathogens with their abundance are harmful and cause huge damage to different agricultural crops and economy of a country as well as lead towards the shortage of food for humans. For their management, the utilization of entomopathogenic fungi is an eco-friendly technique, sustainable to the environment, safe for humans and has promising effect over chemical-based pesticides. This process requires a biochemical mechanism, including the production of enzymes, toxins, and other metabolites that facilitate host infection and invasion. Essential enzymes such as chitinase, proteinase, and lipase play a direct role in breaking down the host cuticle, the primary barrier to EPF (Entomopathogenic Fungi) infection. Additionally, secondary metabolites such as destruxins in Metarhizium, beauvericin in Beauveria, hirsutellides in Hirsutella, isarolides in Isaria, cordyols in Cordyceps, and vertihemipterins in Verticillium, among others, act both directly and indirectly to disable the defense mechanisms of insect hosts, thereby accelerating the EPF infection process. The chemical composition of these secondary metabolites varies, ranging from simple non-peptide pigments such as oosporine to highly complex piperazine derivatives such as vertihemiptellides. The biocontrol efficacy of EPF is extensively studied, with numerous fungal strains commercially available on a large scale for managing arthropod pests. This review emphasizes the role of proteins and enzymes against crop pathogens, detailing their mode of action, and describing the metabolites from entomopathogenic fungi and their biological activities. In doing so, these findings contribute to establishing a symbiotic equilibrium between agricultural productivity and environmental conservation.

Gustatory Receptor 206 Participates in the Foraging Behavior of Larvae of Polyphagous Pest Spodoptera litura

Insect gustatory receptors (GRs) aid in the precise identification of deterrent or stimulant compounds associated with food, mating, and egg-laying. Thus, they are promising targets for developing efficient insecticides. Here, 61 GRs in the chemosensory organs of Spodoptera litura larvae and adults were identified. Among them, SlitGR206 exhibited larval labium (LL)-specific expression characteristics. To explore the role of SlitGR206, a bacterial expression system was established to produce high-quality double-stranded RNA (dsRNA) and suppress SlitGR206 expression in LL. Subsequent behavioral assessments revealed that SlitGR206 silencing influenced larval feeding preferences and absorption. Moreover, it was found to reduce the ability of larvae to forage the five crucial host odorants. These findings demonstrate that SlitGR206 likely plays an indirect regulatory role in host recognition, consequently affecting foraging behavior. This provides a crucial foundation for the analysis of functional diversity among insect GRs and the precise development of nucleic acid pesticides in the future.

A life-and-death struggle: interaction of insects with entomopathogenic fungi across various infection stages

Insects constitute approximately 75% of the world's recognized fauna, with the majority of species considered as pests. Entomopathogenic fungi (EPF) are parasitic microorganisms capable of efficiently infecting insects, rendering them potent biopesticides. In response to infections, insects have evolved diverse defense mechanisms, prompting EPF to develop a variety of strategies to overcome or circumvent host defenses. While the interaction mechanisms between EPF and insects is well established, recent findings underscore that their interplay is more intricate than previously thought, especially evident across different stages of EPF infection. This review primarily focuses on the interplay between EPF and the insect defense strategies, centered around three infection stages: (1) Early infection stage: involving the pre-contact detection and avoidance behavior of EPF in insects, along with the induction of behavioral responses upon contact with the host cuticle; (2) Penetration and intra-hemolymph growth stage: involving the initiation of intricate cellular and humoral immune functions in insects, while symbiotic microbes can further contribute to host resistance; (3) Host insect's death stage: involving the ultimate confrontation between pathogens and insects. Infected insects strive to separate themselves from the healthy population, while pathogens rely on the infected insects to spread to new hosts. Also, we discuss a novel pest management strategy underlying the cooperation between EPF infection and disturbing the insect immune system. By enhancing our understanding of the intricate interplay between EPF and the insect, this review provides novel perspectives for EPF-mediated pest management and developing effective fungal insecticides.

Entomopathogenic fungi based microbial insecticides and their physiological and biochemical effects on Spodoptera frugiperda (J.E. Smith)

Background

'The fall armyworm, Spodoptera frugiperda', represents a significant threat to maize production, a major staple crop in Asian countries.

Methods

In pursuit of more effective control of this insect pest, our study assessed the physiological and biochemical effects of the entomopathogenic fungus Metarhizium anisopliae against the larvae of S. frugiperda.

Results

Results revealed that, following nine days of treatment, a high concentration of conidia (1.5x107 conidia/mL-1) was toxic to all stages of larvae (second to fifth instar), resulting in 97% mortality of the second instar, 89% mortality of the third instar, 77% mortality of the fourth instar, and 72% mortality of fifth instar. All larval instars were found to have dose-dependent mortality effects. Treated S. frugiperda larvae further displayed significant physiological, morphological, and behavioral changes. Here, treated larvae displayed significantly lower levels of acetylcholinesterase, α-carboxylesterase, and β-carboxylesterase enzyme activity when compared to control groups. Treated larvae underwent an outward morphological change as the result of a decrease in the exterior cuticle of the anal papillae and a demelanization of the interior cuticle. Treated larvae also exhibited abnormal feeding behaviors as a consequence of the negative impact of conidia treatment on the neuromuscular system. Investigation into the effect of M. anisopliae on the non-target organism, the earthworm Eudrilus eugeniae, revealed that M. anisopliae conidia did not produce significant pathogenicity following three days of treatment. Furthermore, histological analysis revealed no significant effect of the entomopathogenic fungi on the gut tissue of the non-target organism.

Conclusion

This study highlights the potential of M. anisopliae in the control of S. frugiperda.

Herbicide exposure alters the effect of the enthomopathogen Beauveria bassiana on immune gene expression in mealworm beetles

Concerns have grown worldwide about the potentially far-reaching effects of herbicides on functional biodiversity in agroecosystems. Repeated applications over time can lead to accumulation of residues in soil, water, and food and may have negative impacts on non-target organisms. However, the effects of herbicide residues on interspecific relationships, such as host-pathogen interactions, are poorly studied. In this study, we evaluated the effects of two different concentrations of a commercial pendimethalin-based formulation (PND), the residual contamination (S, 13 ppm) in treated soils and the maximum residue level allowed by the European Commission in cereals (EU, 0.05 ppm). We tested the effect of PND on the biological interaction between the mealworm beetle Tenebrio molitor Linnaeus, 1758 and the entomopathogenic fungus Beauveria bassiana Vuillemin, 1912 (Bb, strain KVL 03-144) at two concentrations (LC50 5 × 105 conidia mL-1 and LC100 1 × 107 conidia mL-1). We checked the survival of beetles exposed to PND or/and inoculated with B. bassiana, the expression of four antimicrobial peptides (AMPs), and finally how PND affects in vitro germination of fungus. The exposure to PND had no significant effects on the survival of either control or Bb-exposed beetles. In the mealworm beetle, upregulation of gene expression of the inducible AMPs Tenecin 1, 2, and 4 was observed in PND-treated beetles after inoculation with Bb, while the levels of the non-inducible AMP Tenecin 3 were similar between treatments. In conclusion, our findings demonstrate that admitted residual doses of currently used herbicides modify an important component of the inducible immune response of an insect. This did not translate into an effect on the survival to B. bassiana in our system. However, residual doses of the herbicide at 13 ppm may temporarily affect fungal germination. These results raise questions about the compatibility of bioinsecticides with synthetic pesticides and the effects of herbicide residues on host-pathogen interactions.

Influence of symbiotic bacteria on the susceptibility of Plagiodera versicolora to Beauveria bassiana infection

The symbiotic bacterial microbiota of insects has been shown to play essential roles in processes related to physiology, metabolism, and innate immunity. In this study, the symbiotic microbiome of Plagiodera versicolora at different developmental stages was analyzed using 16S rRNA high-throughput sequencing. The result showed that symbiotic bacteria community in P. versicolora was primarily made up of Actinobacteriota, Proteobacteria, Firmicutes, Bacteroidota, and Dependentiae. The bacterial composition among different age individuals were highly diverse, while 65 core genera were distributed in all samples which recommend core bacterial microbiome. The 8 species core bacteria were isolated from all samples, and all of them were classified as Pseudomonas sp. Among them, five species have been proven to promote the vegetable growth of Beauveria bassiana. Moreover, the virulence of B. bassiana against nonaxenic larvae exceeded B. bassiana against axenic larvae, and the introduction of the Pseudomonas sp. to axenic larvae augmented the virulence of fungi. Taken together, our study demonstrates that the symbiotic bacteria of P. versicolora are highly dissimilar, and Pseudomonas sp. core bacteria can promote host infection by entomopathogenic fungus. This result emphasizes the potential for harnessing these findings in the development of effective pest management strategies.

Recent Advancements in Pathogenic Mechanisms, Applications and Strategies for Entomopathogenic Fungi in Mosquito Biocontrol

Fungal diseases are widespread among insects and play a crucial role in naturally regulating insect populations. Mosquitoes, known as vectors for numerous infectious diseases, pose a significant threat to human health. Entomopathogenic fungi (EPF) have emerged as highly promising alternative agents to chemical mosquitocides for controlling mosquitoes at all stages of their life cycle due to their unique infection pathway through direct contact with the insect's cuticle. In recent years, significant advancements have been made in understanding the infection pathways and pathogenic mechanisms of EPF against mosquitoes. Various strategies involving the use of EPF alone or combinations with other approaches have been employed to target mosquitoes at various developmental stages. Moreover, the application of genetic technologies in fungi has opened up new avenues for enhancing the mosquitocidal efficacy of EPF. This review presents a comprehensive summary of recent advancements in our understanding the pathogenic mechanisms of EPF, their applications in mosquito management, and the combination of EPF with other approaches and employment of transgenic technologies. The biosafety concerns associated with their use and the corresponding approaches are also discussed. The recent progress suggests that EPF have the potential to serve as a future biorational tool for controlling mosquito vectors.