Specific diversity of the entomopathogenic fungi Beauveria and Metarhizium in Mexican agricultural soils

Entomopathogenic Fungi in Forest Habitats of Ixodes ricinus

(1) Background: In addition to the microclimate, host availability, and tick microbiota, soil environmental microorganisms can affect tick populations. This study aimed to (1) determine the presence and diversity of entomopathogenic fungi (EF) in forests, where ticks are abundant, and (2) estimate the effectiveness of the isolated EF strains against Ixodes ricinus. (2) Methods: EF were isolated using the trap insect method from soil collected from tick sites. A bioassay was used to estimate the effectiveness of EF against ticks. (3) Results: The presence of EF was found in all tested forest habitat types. A total of 53 strains belonging to the genera Metarhizium, Beauveria, and Isaria were isolated. All the six strains subjected to the bioassay showed potential efficacy against both adult and nymphal stages of I. ricinus; however, the strains differed in their effectiveness. The most effective isolate against I. ricinus was the soil environmental strain of Metarhizium anisopliae. (4) Conclusion: The study indicates that tick habitats can be the source of entomopathogenic fungi, which have a lethal effect on ticks, as demonstrated in preliminary laboratory tests with I. ricinus. However, for practical use, extensive field tests and further research on application methods and long-term effects are necessary to develop effective and sustainable tick management strategies.

Genomic Characterization and Functional Description of Beauveria bassiana Isolates from Latin America

Beauveria bassiana is an entomopathogenic fungus used in agriculture as a biological controller worldwide. Despite being a well-studied organism, there are no genomic studies of B. bassiana isolates from Central American and Caribbean countries. This work characterized the functional potential of eight Neotropical isolates and provided an overview of their genomic characteristics, targeting genes associated with pathogenicity, the production of secondary metabolites, and the identification of CAZYmes as tools for future biotechnological applications. In addition, a comparison between these isolates and reference genomes was performed. Differences were observed according to geographical location and the lineages of the B. bassiana complex to which each isolate belonged.

Baseline Analysis of Endophytic Fungal Associates of Solenopsis invicta Buren from Mounds across Five Counties of Guangdong Province, China

Red imported fire ants mounds have been suggested as a potential reservoir for beneficial entomopathogenic fungal species that are vital for more complex roles in the ecosystem aside from infecting the insects. In the current study, the assemblage of fungal symbionts of the red imported fire ants (RIFA) were obtained across five cities in Guangdong Province, China. The sampling areas were selected because of high occurrence of fire ants mounds in the regions. Mound soils, plant debris within mounds, and ants were collected from three sampling locations in each city for potential isolation of entomopathogenic fungal associates of RIFA. All samples were collected during the spring of 2021. Following successful isolation from substrates, the patterns of fungal species composition, and richness were evaluated. In total, 843 isolates were recovered, and based on their phenotypic distinctiveness and molecular characterization based on DNA sequences of multiple loci including the ITS, SSU, and LSU regions, 46 fungal taxa were obtained, including 12 that were unidentified. Species richness and abundance was highest in the mound soils, while the lowest value was recorded from the ant body. As per the different locations, the highest abundance level was recorded in Zhuhai, where 15 fungal taxa were cultivated. The most common taxa across all substrates and locations was Talaromyces diversus. A baseline analysis of the fungal community composition of RIFA would better our understanding on the interactions between these social ants and their associated microbial organisms, and this knowledge in turn would be important for the successful management of the RIFA.

Bioexploration and Phylogenetic Placement of Entomopathogenic Fungi of the Genus Beauveria in Soils of Lebanon Cedar Forests

The cedar forests of Lebanon have been threatened by the outbreak caused by climate change of a web-spinning sawfly, Cephalcia tannourinensis (Hymenoptera: Pamphiliidae), which negatively impacted the survival of one of the oldest tree species on earth. In this study, we investigated the occurrence of naturally soil-inhabiting entomopathogenic fungi for their role in containing the massive outbreak of this insect. We used a combination of fungal bioexploration methods, including insect bait and selective media. Morphological features and multilocus phylogeny-based on Sanger sequencing of the transcripts encoding the translation elongation factor 1-alpha (TEF-α), RNA polymerase II second largest subunit (RBP2), and the nuclear intergenic region (Bloc) were used for species identification. The occurrence rate of entomopathogenic fungi (EPF) varied with location, soil structure, forest structure, and isolation method. From 15 soil samples positive for fungal occurrence, a total of 249 isolates was obtained from all locations using different isolation methods. The phylogenetic analysis confirmed the existence of two novel indigenous species: Beauveria tannourinensis sp. nov. and Beauveria ehdenensis sp. nov. In conclusion, the present survey was successful (1) in optimizing the isolation methods for EPF, (2) investigating the natural occurrence of Beauveria spp. in outbreak areas of C. tannourinensis, and (3) in characterizing the presence of new Beauveria species in Lebanese cedar forest soil.

General Limitations to Endophytic Entomopathogenic Fungi Use as Plant Growth Promoters, Pests and Pathogens Biocontrol Agents

The multiple roles of fungal entomopathogens in host plants' growth promotion, pest and pathogen management have drawn huge attention for investigation. Endophytic species are known to influence various activities of their associated host plants, and the endophyte-colonized plants have been demonstrated to gain huge benefits from these symbiotic associations. The potential application of fungal endophytes as alternative to inorganic fertilizers for crop improvement has often been proposed. Similarly, various strains of insect pathogenic fungi have been formulated for use as mycopesticides and have been suggested as long-term replacement for the synthetic pesticides that are commonly in use. The numerous concerns about the negative effects of synthetic chemical pesticides have also driven attention towards developing eco-friendly pest management techniques. However, several factors have been underlined to be militating the successful adoption of entomopathogenic fungi and fungal endophytes as plant promoting, pests and diseases control bio-agents. The difficulties in isolation and characterization of novel strains, negative effects of geographical location, vegetation type and human disturbance on fungal entomopathogens, are among the numerous setbacks that have been documented. Although, the latest advances in biotechnology and microbial studies have provided means of overcoming many of these problems. For instance, studies have suggested measures for mitigating the negative effects of biotic and abiotic stressors on entomopathogenic fungi in inundative application on the field, or when applied in the form of fungal endophytes. In spite of these efforts, more studies are needed to be done to achieve the goal of improving the overall effectiveness and increase in the level of acceptance of entomopathogenic fungi and their products as an integral part of the integrated pest management programs, as well as potential adoption as an alternative to inorganic fertilizers and pesticides.

Identification and phylogenetic analysis of a collection of Beauveria spp. Isolates from Central America and Puerto Rico

The genus Beauveria comprises economically important entomopathogenic fungi, widely used for biological control in agriculture. Interest in these organisms in Costa Rica prompted surveys and establishment of collections in the past two decades. However, there was neither a formal identification nor a characterization of the isolates. With that purpose, the morphology and genetic variation by microsatellites and partial sequencing of Bloc, TEF-1α and RPB2 regions were studied for 32 isolates of Beauveria, which included 26 from Costa Rica, five from Puerto Rico and one from Honduras. The isolates were identified as B. bassiana (29) and B. caledonica (3). Ninety-three percent of B. bassiana isolates belonged to a monophyletic group of African and Neotropical isolates. A total of 105 alleles were recorded with 11 SSR markers, and the results suggested high diversity within the collection. Mantel tests showed low association between geographic origin and the variation among isolates.

Advances in Entomopathogen Isolation: A Case of Bacteria and Fungi

Entomopathogenic bacteria and fungi are quite frequently found in soils and insect cadavers. The first step in utilizing these microbes as biopesticides is to isolate them, and several culture media and insect baiting procedures have been tested in this direction. In this work, the authors review the current techniques that have been developed so far, in the last five decades, and display brief protocols which can be adopted for the isolations of these entomopathogens. Among bacteria, this review focuses on Serratia spp. and bacteria from the class Bacilli. Among fungi, the review focuses those from the order Hypocreales, for example, genera Beauveria, Clonostachys, Lecanicillium, Metarhizium, and Purpureocillium. The authors chose these groups of entomopathogenic bacteria and fungi based on their importance in the microbial biopesticide market.

Sensitivity of Ixodes ricinus (L., 1758) and Dermacentor reticulatus (Fabr., 1794) ticks to entomopathogenic fungi isolates: preliminary study

Entomopathogenic fungi of the genus Beauveria and Metarhizium play an important role in controlling the population of arthropods. However, the data on their effectiveness against ticks focus mainly on species that do not occur in Europe. The aim of the study was to assess the effectiveness of entomopathogenic fungi against two of the most important tick species in Europe: Ixodes ricinus and Dermacentor reticulatus. In our study, the majority of tested entomopathogenic fungi strains showed potential efficacy against both tick species; however, D. reticulatus was less susceptible in comparison to I. ricinus. The observed mortality of ticks was up to 100% by using all commercial strains as well as three out of nine of the environmental strains. Among all tested fungi, the most effective against both tick species was environmental strain Metarhizium anisopliae LO4(1) with LC₅₀ values: 2.6 × 10³ cfu/ml–5.7 × 10⁵ cfu/ml. Botanigard proved to be more effective than MET52 with LC₅₀ values: 6.8 × 10³ cfu/ml–3.3 × 10⁶ cfu/ml. The conducted bioassays indicate the potential possibility of using the environmental isolates of entomopathogenic fungi, as well as commercial strains in control of local populations of I. ricinus and D. reticulatus; however, the possibility of using them in vivo requires more research.

Selection of Beauveria bassiana (Hypocreales: Cordycipitaceae) strains to control Xyleborus affinis (Curculionidae: Scolytinae) females

BACKGROUND

Xyleborus affinis Eichhoff (Coleoptera: Curculionidae) is an ambrosia beetle reported to affect avocado trees (Persea americana Mill.). The use of the entomopathogenic fungus (EPF) Beauveria bassiana (Bals.-Criv.) Vuill. for ambrosia beetle control represents an alternative to insecticides.

METHODS

This study was designed in two stages to select B. bassiana strains with potential to control X. affinis females. In the first stage, 19 B. bassiana Mexican strains from EPF collection, isolated from Coleoptera (CHE-CNRCB, http://www.gob.mx/senasica/documentos/coleccion-de-hongos-entomopatogenos), were tested. Analyses included radial growth rate, conidial yield, spore germination, and germ tube length. Results were analysed by Principal Component Analysis (PCA) to identify clusters within favourable growth phenotypes. For the second stage, 10 selected strains were re-analysed for virulence-related metabolic characteristic, including cell wall-bound cuticle-degrading enzymes-Pr1-like proteases and β-N-acetyl glucosaminidases (NAGase) chitinases, conidial hydrophobicity and monopolar germination parameters. A second PCA analysis was run for those virulence parameters analysed, and upon results strains CHE-CNRCB 44, 171, 431 and 485 were selected and tested against X. affinis females. Females were treated with a 1 × 108 conidia mL-1 suspension (recommended rate), using a Potter Tower.

RESULTS

All strains showed insecticidal activity, inducing up to 58% mortality; about 30% dead beetles developed aerial mycelia (CHE-CNRCB 485) and the fastest mortality rate was t0 = 1.95 (CHE-CNRCB 44).

CONCLUSION

Since all selected strains showed virulence against X. affinis females, results indicated the possibility of selecting B. bassiana strains based on multiple metabolic attributes, as a preliminary test to perform bioassays against order-related target insects.

Occurrence, Identification, and Virulence of Native Fungal Pathogens Isolated From Mexican Fruit Fly (Diptera: Tephritidae) Larvae From Soils of Three Cropping Systems

The Mexican fruit fly, Anastrepha ludens Loew, is a significant pest in mango and citrus production areas of Mexico. In this study, we evaluated the effects of some geographic characteristics, rainfall period, soil micro-environmental, and soil coverage variables on the occurrence of entomopathogenic fungi (EPF) associated with A. ludens larvae in soils of mango, grapefruit and mixed crops in central Veracruz state, Mexico. EPF isolates were characterized morphologically and identified by sequence analysis of elongation factor (EF1-1018F, EF1-1620R). We recorded four species of EPF (Metarhizium robertsii J.F. Bisch, S.A. Rehner & Humber [Hypocreales: Cordycipitaceae], M. brunneum Petch [Hypocreales: Cordycipitaceae], M. pinghaense Q.T. Chen & H.L. Guo [Hypocreales: Cordycipitaceae], and Beauveria bassiana (Balsamo) Vuillemin [Hypocreales: Cordycipitaceae]), of which Metarhizium robertsii was the most abundant and the most virulent. Also, we found that rainfall period, organic matter, coverage of herbs and forbs, and calcium levels modulated EPF occurrence. We estimated lethal concentrations for A. ludens larvae of the four most promising isolates, V3-123, V3-160, V1-332, and V3-369. Our results suggest that M. robertsii obtained from agricultural soils holds potential as a biological control agent for A. ludens.

Virulence of Some Entomopathogenic Fungi Isolates of Beauveria bassiana (Hypocreales: Cordycipitaceae) and Metarhizium anisopliae (Hypocreales: Clavicipitaceae) to Aulacaspis tubercularis (Hemiptera: Diaspididae)and Icerya seychellarum (Hemiptera: Monophlebidae) on Mango Crop

Six fungal isolates of Beauveria bassiana (Balsamo) Vuillemin and one isolate of Metarhizium anisopliae (Metschnikoff) Sorokin were isolated and evaluated for their pathogenicity to Icerya seychellarum (Westwood) and Aulacaspis tubercularis Newstead. There is a positive correlation between the concentration of the fungal blastospore concentrations and the percentage of mortality. Bio-efficacy increased significantly after inoculation with increasing concentration of blastospores and elapsed time up to 12 d after inoculation. The mortality of nymphs exposed to fungal isolates at various concentrations varied between 2.5 and 88.8%. Probit analysis of data at 95% confidence limits of LC50 and LT50s showed significant differences in the susceptibility of nymphs of I. seychellarum and A. tubercularis to the tested fungal isolates. The fungal isolates of Egy-6 and Egy-9 were the most effective against I. seychellarum and A. tubercularis, respectively. They had the lowest LC50 (4.20 × 105 and 5.71 × 103 blastospore ml-1) and LT50 (ranged from 4.61 to 9.79 and 4.84 to 8.71 d), respectively. The current study showed that all the fungal isolates yielded moderate mortality rates of nymphs and adult female populations of both the tested insect pests. To our knowledge, this is the first report of bio-efficacy of Beauveria and Metarhizium isolates against members of the Diaspidadae and Monophlebidae family insects. These results establish that the use of these native entomopathogenic fungi isolates of B. bassiana (Egy-3, Egy-4, Egy-6, Egy-7, Egy-9, and Egy-10) and M. anisopliae (Egy-5) could be considered for further development as microbial control agents of the mealybug and scale insects as a potential biological agent for use in an IPM program.

Occurrence and diversity of entomopathogenic fungi (Beauveria spp. and Metarhizium spp.) in Australian vineyard soils

Entomopathogenic Ascomycetes: Hypocreales fungi occur worldwide in the soil; however, the abundance and distribution of these fungi in a vineyard environment is unknown. A survey of Australian vineyards was carried out in order to isolate and identify entomopathogenic fungi. A total of 240 soil samples were taken from eight vineyards in two states (New South Wales and Victoria). Insect baiting (using Tenebrio molitor) and soil dilution methods were used to isolate Beauveria spp. and Metarhizium spp. from all soil samples. Of the 240 soil samples, 60% contained either Beauveria spp. (26%) or Metarhizium spp. (33%). Species of Beauveria and Metarhizium were identified by sequencing the B locus nuclear intergenic region (Bloc) and elongation factor-1 alpha (EFT1) regions, respectively. Three Beauveria species (B. bassiana, B. australis and B. pseudobassiana) and six Metarhizium species (M. guizhouense, M. robertsii, M. brunneum, M. flavoviride var. pemphigi, M. pingshaense and M. majus) were identified. A new sister clade made up of six isolates was identified within B. australis. Two potentially new phylogenetic species (six isolates each) were found within the B. bassiana clade. This study revealed a diverse community of entomopathogenic fungi in sampled Australian vineyard soils.

Entomopathogenic fungi in Portuguese vineyards soils: suggesting a 'Galleria-Tenebrio-bait method' as bait-insects Galleria and Tenebrio significantly underestimate the respective recoveries of Metarhizium (robertsii) and Beauveria (bassiana)

Entomopathogenic fungi (EPF) are the natural enemies of insect-pests. However, EPF recoveries can be influenced by the soil habitat-type(s) incorporated and/or the bait-insect(s) used. Galleriamellonella (GM) as bait-insect, i.e. 'Galleria-bait', is arguably the most common methodology, which is sometimes used solely, to isolate EPF from soils. Insect baiting using Tenebriomolitor (TM) has also been employed occasionally. Here 183 soils were used to estimate the functional diversity of EPF in Portuguese Douro vineyards (cultivated habitat) and adjacent hedgerows (semi-natural habitat), using the TM bait method. Moreover, to study the effect of insect baiting on EPF recovery, 81 of these 183 soil samples were also tested for EPF occurrences using the GM bait method. Twelve species were found in 44.26% ± 3.67% of the total of 183 soils. Clonostachysroseaf.rosea was found in maximum soils (30.05% ± 3.38%), followed by Beauveriabassiana (12.57% ± 2.37%), Purpureocilliumlilacinum (9.29% ± 2.14%) and Metarhiziumrobertsii (6.01% ± 1.75%). Beauveriapseudobassiana (P < 0.001), C.roseaf.rosea (P = 0.006) and Cordycepscicadae (P=0.023) were isolated significantly more from hedgerows, highlighting their sensitivities towards agricultural disturbances. Beauveriabassiana (P = 0.038) and M.robertsii (P = 0.003) were isolated significantly more using GM and TM, respectively. Principal component analysis revealed that M.robertsii was associated both with TM baiting and cultivated habitats, however, B.bassiana was slightly linked with GM baiting only. Ecological profiles of B.bassiana and P.lilacinum were quite similar while M.robertsii and C.roseaf.rosea were relatively distant and distinct. To us, this is the first report on (a) C.cicadae isolation from Mediterranean soils, (b) Purpureocilliumlavendulum as an EPF worldwide; and (c) significant recoveries of M.robertsii using TM over GM. Overall, a 'Galleria-Tenebrio-bait method' is advocated to study the functional diversity of EPF in agroecosystems.

Entomopathogenic fungi in Portuguese vineyards soils: suggesting a ‘Galleria-Tenebrio-bait method’ as bait-insects Galleria and Tenebrio significantly underestimate the respective recoveries of Metarhizium (robertsii) and Beauveria (bassiana)

Entomopathogenic fungi (EPF) are the natural enemies of insect-pests. However, EPF recoveries can be influenced by the soil habitat-type(s) incorporated and/or the bait-insect(s) used. Galleriamellonella (GM) as bait-insect, i.e. ‘Galleria-bait’, is arguably the most common methodology, which is sometimes used solely, to isolate EPF from soils. Insect baiting using Tenebriomolitor (TM) has also been employed occasionally. Here 183 soils were used to estimate the functional diversity of EPF in Portuguese Douro vineyards (cultivated habitat) and adjacent hedgerows (semi-natural habitat), using the TM bait method. Moreover, to study the effect of insect baiting on EPF recovery, 81 of these 183 soil samples were also tested for EPF occurrences using the GM bait method. Twelve species were found in 44.26% ± 3.67% of the total of 183 soils. Clonostachysroseaf.rosea was found in maximum soils (30.05% ± 3.38%), followed by Beauveriabassiana (12.57% ± 2.37%), Purpureocilliumlilacinum (9.29% ± 2.14%) and Metarhiziumrobertsii (6.01% ± 1.75%). Beauveriapseudobassiana (P &lt; 0.001), C.roseaf.rosea (P = 0.006) and Cordycepscicadae (P=0.023) were isolated significantly more from hedgerows, highlighting their sensitivities towards agricultural disturbances. Beauveriabassiana (P = 0.038) and M.robertsii (P = 0.003) were isolated significantly more using GM and TM, respectively. Principal component analysis revealed that M.robertsii was associated both with TM baiting and cultivated habitats, however, B.bassiana was slightly linked with GM baiting only. Ecological profiles of B.bassiana and P.lilacinum were quite similar while M.robertsii and C.roseaf.rosea were relatively distant and distinct. To us, this is the first report on (a) C.cicadae isolation from Mediterranean soils, (b) Purpureocilliumlavendulum as an EPF worldwide; and (c) significant recoveries of M.robertsii using TM over GM. Overall, a ‘Galleria-Tenebrio-bait method’ is advocated to study the functional diversity of EPF in agroecosystems.

Species Diversity and Population Dynamics of Entomopathogenic Fungal Species in the Genus Metarhizium-a Spatiotemporal Study

We studied the species diversity and population genetic structure of isolates of fungi from the entomopathogenic genus Metarhizium that had been isolated from sugarcane crops and surrounding grass. Soil and leaf samples were taken on four sampling occasions over 13 months (October 2014-October 2015). Isolations were made using the Galleria mellonella baiting method and selective media. Phylogenetic placement of isolates was done by sequencing a fragment of the 5' of the elongation factor 1-α gene (EF1-α). Population genetic structure was determined by analysing this sequence information using AMOVA and Haplotype network analyses. Genotypic diversity was studied using microsatellite genotyping. The most abundant species was M. anisopliae s.s. (80 isolates), then M. pingshaense (three isolates), and M. guizhouense (one isolate). More than 50% of the genetic variation was explained by the time the samples were collected regardless of plant host association. Some haplotypes were found on the first sampling date and then not found on subsequent sampling dates, while other haplotypes were found initially, disappeared, but then found again on the last sampling date. To the best of our knowledge, this is the first report of the population genetic structure of M. anisopliae species in time and space. The effect of abiotic factors is discussed.

Managing the plant microbiome for biocontrol fungi: examples from Hypocreales

Feeding an increasing global population requires continued improvements in agricultural efficiency and productivity. Meeting estimated future production levels requires the adoption of practices that increase output without environmental degradation associated with external inputs to supplement nutrition or control pests. Enriching the community of microbes associated with plants in agricultural systems for those providing ecosystem services such as pest control is one possible component towards achieving sustainable productivity increases. In this review we explore the current state of knowledge for Hypocreales fungi used in biological control. Advances in understanding the field ecology, diversity and genetic determinants of host range and virulence of hypocrealean fungi provide the means to improve their efficacy.

Phylogenetic structure and habitat associations of Beauveria species isolated from soils in Slovakia

The phylogenetic structure of 109 soil-borne entomopathogenic Beauveria isolates acquired using the Galleria mellonella bait method from different habitat types in Slovakia was determined by sequence analysis of their ITS and Bloc loci. Three Beauveria species were identified; Beauveria bassiana, B. pseudobassiana and B. brongniartii, represented by 51.4%, 43.1% and 5.5% of acquired isolates, respectively, which were resolved into 15, 1 and 1 distinguishable haplotypes. Correlation analysis with the habitat type and individual habitat characteristics showed strong preferences of the most prevalent haplotypes for agricultural (B. bassiana A1) and forest habitats (B. pseudobassiana) which has possible implications for conservative biocontrol strategies.