Increased mortality of the European pepper moth Duponchelia fovealis (Lepidoptera:Crambidae) using entomopathogenic fungal consortia

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.

UV-induced mutagenesis of Beauveria bassiana (Hypocreales: Clavicipitaceae) yields two hypervirulent isolates with different transcriptomic profiles

BACKGROUND

The fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae) can infest over 300 plant species and cause huge economic losses. Beauveria bassiana (Hypocreales: Clavicipitaceae) is one of the most widely used entomopathogenic fungi (EPF). Unfortunately, the efficacy of B. bassiana against S. frugiperda is quite low. Hypervirulent EPF isolates can be obtained by ultraviolet (UV)-irradiation. Here we report on the UV-induced mutagenesis and transcriptomic analysis of B. bassiana.

RESULTS

The wild-type (WT) B. bassiana (ARSEF2860) was exposed to UV light to induce mutagenesis. Two mutants (named 6M and 8M) showed higher growth rates, conidial yields, and germination rates compared to the WT strain. The mutants showed higher levels of tolerance to osmotic, oxidative, and UV stresses. The mutants showed higher protease, chitinase, cellulose, and chitinase activities than WT. Both WT and mutants were compatible with the insecticides matrine, spinetoram, and chlorantraniliprole, but incompatible with emamectin benzoate. Insect bioassays showed that both mutants were more virulent against S. frugiperda and the greater wax moth Galleria mellonella. Transcriptomic profiles of the WT and mutants were determined by RNA-sequencing. The differentially expressed genes (DEGs) were identified. The gene set enrichment analysis (GSEA), protein-protein interaction (PPI) network, and hub gene analysis revealed virulence-related genes.

CONCLUSION

Our data demonstrate that UV-irradiation is a very efficient and economical technique to improve the virulence and stress resistance of B. bassiana. Comparative transcriptomic profiles of the mutants provide insights into virulence genes. These results provide new ideas for improving the genetic engineering and field efficacy of EPF. © 2023 Society of Chemical Industry.

Fungal consortium of two Beauveria bassiana strains increases their virulence, growth, and resistance to stress: A metabolomic approach

The use of two or more microorganisms in a microbial consortium has been increasingly applied in the biological control of diseases and pests. Beauveria bassiana is one of the most widely studied fungal species in biological control, yet little is known about its role in fungal consortiums. In a previous study, our group found that a consortium formed by two strains of B. bassiana had significantly greater biocontrol potential against the polyphagous caterpillars Duponchelia fovealis (Lepidoptera: Crambidae) than either strain on its own. In this study, we use GC-MS and LC-MS/MS to evaluate and discuss the metabolomics of the consortium. A total of 21 consortium biomarkers were identified, corresponding to 14 detected by LC-MS/MS and seven by GC-MS. Antioxidant and anti-inflammatory mechanisms are the main properties of the metabolites produced by the consortium. These metabolites can depress the insect’s immune system, increasing its vulnerability and, hence, the fungal virulence of the consortium. In light of these results, we propose an action model of insect mortality due to the metabolites secreted by the consortium. The model includes the inhibition of defense mechanisms such as pro-inflammatory interleukin secretion, cell migration, cell aggregation, Dif, Dorsal and Relish gene transcription, and JAK/STAT and JNK signaling pathways. It also promotes the cleaning of oxidative molecules, like ROS, NOS, and H₂O₂, and the induction of virulence factors.

Virulence of the Bio-Control Fungus Purpureocillium lilacinum Against Myzus persicae (Hemiptera: Aphididae) and Spodoptera frugiperda (Lepidoptera: Noctuidae)

Eco-friendly entomopathogenic fungi are widely used to control agricultural insect pests. Purpureocillium lilacinum (Thom.) Luangsa-ard et al. (Hypocreales: Ophiocordycipitaceae) is a nematophagous fungus used for the bio-control of destructive root-knot nematodes. However, its insecticidal activities against agricultural insect pests haven't been widely studied. In this study, P. lilacinum PL-1 was isolated from soil (Hefei, China) and identified by molecular and morphological analyses. The growth rate, spore production, proteinase, and chitinase activities of the isolate were analyzed. Virulence tests against green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae) and fall armyworm (FAW), Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae) were performed. The median lethal concentration (LC50) and median lethal time (LT50) against aphids (via immersion) and LT50 against FAW (via injection) were determined. FAW eggs immersed in aqueous conidia suspension were infected after 60 h. Differentially expressed genes (DEGs) in the infection of FAW larvae by P. lilacinum were analyzed by quantitative reverse transcription PCR. The significantly upregulated DEGs include FAW immune genes (antimicrobial peptides, C-type lectins, lysozymes, prophenoloxidase, and peptidoglycan recognition proteins) and fungal pathogenic genes (ligase, chitinase, and hydrophobin). Our data demonstrate that P. lilacinum can be used as an entomopathogenic fungus against agricultural insect pests.

Biocontrol of Melolontha spp. Grubs in Organic Strawberry Plantations by Entomopathogenic Fungi as Affected by Environmental and Metabolic Factors and the Interaction with Soil Microbial Biodiversity

The efficacy of two strains of two Beauveria species (B. bassiana and B. brongniartii), individually or as co-inoculants, to control Melolontha sp. grubs was assessed in two organic strawberry plantations in relation to the environmental conditions, their abundance after soil inoculation, and their in vitro chitinolytic activity, thereby also verifying their impact on soil microbial communities. A reduction of the grubs' damage to strawberry plants was observed when compared to the untreated control in one plantation, irrespective of the strain used and whether they were applied as single or as co-inoculum. The metabolic pattern expressed by the two fungi in vitro was different: B. bassiana showed a higher metabolic versatility in the use of different carbon sources than B. brongniartii, whose profile was partly overlapped in the co-inoculum. Similar differences in the chitinolytic activity of each of the fungi and the co-inoculum were also pointed out. A higher abundance of B. bassiana in the soils receiving this species in comparison to those receiving B. brongniartii, together with its in vitro metabolic activity, could account for the observed diverse efficacy of pest damage control of the two species. However, environmental and climatic factors also affected the overall efficacy of the two bioinocula. According to the monitoring of the two species in soil, B. bassiana could be considered as a common native species in the studied locations in contrast to B. brongniartii, which seemed to be a non-endemic species. Nevertheless, the inoculation with both species or the co-inoculum did not consistently affect the soil microbial (fungi and bacteria) biodiversity, as expressed by the operational taxonomic unit (OTU) number and Shannon-Wiener diversity index based on terminal restriction fragment length polymorphism (TRFLP) data. A small transient increase of the share of the inoculated species to the total fungal community was noted by the analysis of genes copy numbers only for B. brongniartii at the end of the third growing season.