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

The infection efficacy of Metarhizium strains (Hypocreales: Clavicipitaceae) against the Queensland fruit fly Bactrocera tryoni (Diptera: Tephritidae)

The Queensland fruit fly (Qfly), Bactrocera tryoni Froggatt, is a devastating pest of Australia's commercial fruit systems. Fruit fly mitigation is heavily centered around the use chemical insecticides, with limited investigation into microbial control alternatives. The wet tropics of northern Queensland is a highly biodiverse ecosystem containing many species of insect pathogenic fungi, but it is unclear whether any of these entomopathogens could contribute to Qfly management programs. In laboratory trials, we investigated the potential for Qfly microbial control by 3 locally sourced strains of entomopathogenic fungi comprising 2 species, Metarhizium guizhouense (Chen and Guo) and Metarhizium lepidiotae (Driver and Milner). Additionally, we evaluated 2 different inoculation methods to derive the most effective way to expose the flies to conidia-either through dry conidia or in a conidial suspension. All 3 strains were successful in causing Qfly mortality. Metarhizium lepidiotae resulted in the highest mean mortality over the trials, while M. guizhouense resulted in the highest mortality in a single replicate. Laboratory experiments revealed exposure through dry conidia to be the most effective method to inoculate the flies. These results suggest that fungal entomopathogens could be a viable pathway to Qfly suppression.

Beauveria australis finds a new host in French dung beetles introduced to Australia

Exotic dung beetles have been introduced to Australia for over 50 years to mitigate issues caused by dung produced by livestock. This study aims at identifying fungi affecting a beetle colony and investigating their source. Fungal hyphae emerging from the cuticle of dead beetles were cultured and a multigene phylogeny showed that Beauveria bassiana and B. australis both infected these introduced beetles, likely acquired through local soil or dung. This is the first record of B. australis infecting family Scarabaeidae. This study highlights the importance of fungal outbreak management in insect rearing before release, and challenges associated with new pathogens.

Three Methods Assessing the Association of the Endophytic Entomopathogenic Fungus Metarhizium robertsii with Non-Grafted Grapevine Vitis vinifera

Characterizing the association of endophytic insect pathogenic fungi (EIPF) with plants is an important step in order to understand their ecology before using them in biological control programs. Since several methods are available, it is challenging to identify the most appropriate for such investigations. Here, we used two strains of Metarhizium robertsii: EF3.5(2) native to the French vineyard environment and ARSEF-2575-GFP a laboratory strain expressing a green fluorescent protein, to compare their potential of association with non-grafted grapevine Vitis vinifera. Three methods were used to evaluate the kinetics of rhizosphere and grapevine endospheric colonization: (i) Droplet Digital (ddPCR), a sensitive molecular method of M. robertsii DNA quantification in different plant parts, (ii) culture-based method to detect the live fungal propagules from plant tissues that grew on the medium, (iii) confocal imaging to observe roots segments. Both strains showed evidence of establishment in the rhizosphere of grapevines according to the culture-based and ddPCR methods, with a significantly higher establishment of strain EF3.5(2) (40% positive plants and quantified median of exp(4.61) c/μL) compared to strain ARSEF-2575-GFP (13% positive plants and quantified median of exp(2.25) c/μL) at 96-98 days post-inoculation. A low incidence of association of both strains in the grapevine root endosphere was found with no significant differences between strains and evaluation methods (15% positive plants inoculated with strain EF3.5(2) and 5% with strain ARSEF-2575-GFP according to culture-based method). ddPCR should be used more extensively to investigate the association between plants and EIPF but always accompanied with at least one method such as culture-based method or confocal microscopy.

Discovery of two hypocrealean fungi infecting spotted lanternflies, Lycorma delicatula: Metarhizium pemphigi and a novel species, Ophiocordyceps delicatula

In the eastern United States, populations of the invasive spotted lanternfly, Lycorma delicatula, can be infected by native fungal entomopathogens, including Batkoa major and Beauveria bassiana. In some areas of southeastern Pennsylvania, localized population collapses have been observed in L. delicatula populations to be caused by these pathogens. Two additional fungal pathogens were discovered infecting L. delicatula at low levels, and these were identified as Metarhizium pemphigi and Ophiocordyceps delicatula, a new species that has not been previously described. Therefore, four species of native entomopathogenic fungi have now been documented infecting this abundant, invasive planthopper that is spreading in the United States.

Effect of earthworm Eisenia fetida epidermal mucus on the vitality and pathogenicity of Beauveria bassiana

Beauveria bassiana is one of the most widely studied and used entomopathogenic fungus as biopesticide. In the biological control of pests, B. bassiana will persist in the soil after application, and will inevitably contact with earthworms, especially the epigeic earthworm species. So, what are the effects of earthworm and its epidermal mucus on the activity of B. bassiana? We employed the epigeic earthworm Eisenia fetida, B. bassiana TST05 strain, and the insect Atrijuglans hetaohei mature larvae to study the impact of earthworm epidermal mucus on the vitality and pathogenicity of B. bassiana to insect. Methods included scanning electron microscope observation, detection of spore germination, fungal extracellular enzyme activity, and infection testing to A. hetaohei. The results showed that the B. bassiana spores may attach to the cuticle of E. fetida but they could be covered by the epidermal mucus and became rough and shrunken. After treatment with the epidermal mucus, the spore germination and extracellular enzymes of B. bassiana was significantly inhibited. Inoculation of A. hetaohei larvae with a mixture of B. bassiana and mucus showed that the mucus could reduce the pathogenicity of B. bassiana to the insect, resulting in a slower disease course and lower mortality. It was concluded that the epidermal mucus of the earthworm E. fetida can inhibit the activity of B. bassiana, as well as the infectivity and pathogenicity of fungus to target insects. However, after treatment with epidermal mucus the surviving B. bassiana still had certain infectivity to insects. This is of great significance for the application of B. bassiana in biological control of pests.

Characterisation of Metarhizium majus (Hypocreales: Clavicipitaceae) isolated from the Western Cape Province, South Africa

Entomopathogenic fungi (EPF) are important soil-dwelling entomopathogens, which can be used as biological control agents against pest insects. EPF are capable of causing lethal epizootics in pest insect populations in agroecosystems. During a survey of the orchard soil at an organic farm, different EPF species were collected and identified to species level, using both morphological and molecular techniques. The EPF were trapped from soil samples taken from an apricot orchard. The traps, which were baited in the laboratory, used susceptible host insects, including the last-instar larvae of Galleria mellonella (wax moth larvae) and Tenebrio molitor (mealworm larvae). The potential pathogenicity of the local Metarhizium majus isolate was tested and verified using susceptible laboratory-reared last-instar T. molitor larvae. The identification of the M. majus isolated from South African soil was verified using both morphological and molecular techniques. The occurrence of M. majus in the South African soil environment had not previously been reported.

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.

Genetic structure of Metarhizium species in western USA: Finite populations composed of divergent clonal lineages with limited evidence for recent recombination

Globally distributed, soil associated Metarhizium species used in insect biological control are evidently facultatively sexual and obligately outcrossing, yet sexual morphs have not been observed for most species and corroboration that they recombine in nature remains limited. Community-wide genetic diversity of Metarhizium species among 480 soil isolates from 14 states of western USA was investigated to assess the contributions of clonality and recombination in determining each species' population structure. Seven species, varying greater than 100-fold in relative abundance, were identified by phylogenetic analysis of 5' EF1-α (5TEF), including M. robertsii (n = 372), M. guizhouense (n = 37), M. brunneum (n = 37), M. lepidiotae (n = 14), M. pemphigi (n = 11), M. anisopliae (n = 7) and M. pingshaense (n = 2). Analyses of composite multilocus genotypes integrating 5TEF sequences, multilocus microsatellites and mating type idiomorphs conducted on a subset of 239 isolates revealed that all species populations display pronounced clonal structure. Following clone-correction procedures to remove redundant clonal genotypes and collapse clonal lineages, each species' population sample was determined to be composed of a dozen or fewer genetically unique individuals. Thus, the Metarhizium community inhabiting western USA is conservatively estimated to comprise as few as 34 distinct genetic individuals, with a single, geographically ubiquitous clonal lineage of M. robertsii constituting 45% of total isolates. M. robertsii was the only population determined to be in linkage equilibrium. However, the high proportion of private alleles differentiating most M. robertsii clonal lineages argues against contemporary panmixia, thus the recombination signal detected may be historical. Nevertheless, within M. robertsii, M. brunneum and M. guizhouense there are closely related genotypes of opposite mating type, which suggests that if recombination is contemporary, it likely occurs between closely related individuals. The restricted number of genetic individuals observed throughout western North American Metarhizium species may signify that these represent peripheral populations descended from limited numbers of founders among which there has been little recombination relative to the extent of clone expansion and within-clone genetic divergence.

Applications of Beauveria bassiana (Hypocreales: Cordycipitaceae) to Control Populations of Spotted Lanternfly (Hemiptera: Fulgoridae), in Semi-Natural Landscapes and on Grapevines

Spotted lanternfly, Lycorma delicatula (White), is an invasive Asian insect that was initially found in Berks County, Pennsylvania, in 2014. As of early 2020, this pest had been found in five more eastern states and it is expected to continue to expand its geographical range. Lycorma delicatula is highly polyphagous but seems to prefer tree-of-heaven, Ailanthus altissima. However, grape growers in Pennsylvania have reported significant damage and loss of vines caused by L. delicatula adults. In fall 2018, two fungal entomopathogens (Beauveria bassiana and Batkoa major) drove localized collapses in L. delicatula populations in Berks County, Pennsylvania. In 2019, we tested applications of a commercialized mycoinsecticide based on B. bassiana strain GHA on L. delicatula populations in a public park in southeastern Pennsylvania. A single application of B. bassiana reduced fourth instar nymphs by 48% after 14 d. Applications of B. bassiana to L. delicatula adults in the same park resulted in 43% mortality after 14 d. Beauveria bassiana spores remained viable on foliage for 5-7 d after spraying. We also conducted semi-field bioassays with B. bassiana GHA (formulated as BoteGHA and Aprehend) and another mycoinsecticide containing Isaria fumosorosea Apopka Strain 97 against L. delicatula adults feeding on potted grapes. All the mycoinsecticides killed ≥90% of adults after 9 d using direct applications. Aprehend killed 99% of adults after 9 d with exposure to residues on sprayed grapes. These data show that fungal entomopathogens can help to suppress populations of L. delicatula in agroecosystems and natural areas.

Meta-Analysis and Evaluation by Insect-Mediated Baiting Reveal Different Patterns of Hypocrealean Entomopathogenic Fungi in the Soils From Two Regions of China

A survey was carried out on forest soils and grassland soils from Hebei and Sichuan provinces using Tenebrio molitor larvae as a bait, and high-throughput DNA sequencing (HTS) of the fungal internal transcribed spacer-2 ribosomal DNA was used to monitor the natural distribution of three leading hypocrealean families of insect fungal pathogens (Clavicipitaceae, Cordycipitaceae, and Ophiocordycipitaceae). The occurrence of insect fungal pathogens in soil samples from 98 different sites was compared. The use of insect bait indicated that entomopathogenic fungi of the genus Metarhizium were predominant, followed by Beauveria and Isaria. Molecular characterization using the Mz_FG543 intergenic region revealed that the Metarhizium species pool was phylogenetically composed of three closely related species as follows; Metarhizium pingshaense (n = 74), Metarhizium robertsii (n = 51), and Metarhizium brunneum (n = 26), as well as one isolate which clustered with Metarhizium flavoviride. Nine potentially new phylogenetic species were delimited within the M. flavoviride species complex by sequencing of the 5′ elongation factor-1 alpha region locus. The Beauveria (n = 64) and Isaria (n = 5) isolates were characterized via sequence analyses of the Bloc region. An intergenic spacer phylogeny of the Beauveria isolate assemblage revealed the phylogenetic species within the Beauveria bassiana clade. Interestingly, the individuals of M. pingshaense (n = 18) and M. brunneum (n = 12) exhibited the presence of both mating types in Sichuan Province. Similarly, for the Beauveria isolates, reproductive mode assays demonstrated that all four B. bassiana subclades possessed bipolar outcrossing mating systems. Of these, 19 isolates contained two mating types, and the rest were fixed for single mating types, revealing opportunities for intra-lineage heterothallic mating. The HTS results showed a significantly higher occurrence of the Clavicipitaceae family and the Metarhizium genus in the soil samples. The Venn diagram showed Metarhizium anisopliae (senso lato), Isaria farinose, and B. bassiana as frequently abundant fungal pathogen operational taxonomic units (core) across sampling sites, while the baiting method showed that the genus of Isaria was isolated locally. The Mantel test verified that community dissimilarity increased significantly with geographical distance, suggesting that geographical coordinates are possible factors that influence the insect fungal pathogen community composition in the studied sites. This study is the first to highlight the usefulness of utilizing soil baiting and deep sequencing to investigate the population dynamics of entomopathogens in soil.

Patterns of Occurrence and Activity of Entomopathogenic Fungi in the Algarve (Portugal) Using Different Isolation Methods

Entomopathogenic fungi (EPF) are distributed in natural and agricultural soils worldwide. To investigate EPF occurrence in different botanical habitats and soil-ecoregions, we surveyed 50 georeferenced localities in the spring of 2016 across the Algarve region (South Portugal). Additionally, we compared three EPF isolation methods: insect baiting in untreated or pre-dried-soil and soil dilution plating on a selective medium. We hypothesized that forest habitats (oak and pine semi-natural areas) and the acidic soil ecoregion may favor EPF occurrence. Overall, EPF species were present in 68% of sites, widely distributed throughout the Algarve. The use of selective media resulted in higher recovery of EPF than did either soil-baiting method. Contrary to our hypothesis, neither vegetation type nor ecoregion appeared to influence EPF occurrence. Traditional and molecular methods confirmed the presence of five EPF species. Beauveria bassiana (34% of sites), was the most frequently detected EPF, using pre-dried soil baiting and soil dilution methods. However, baiting untreated soil recovered Fusarium solani more frequently (26% of sites), demonstrating the utility of using multiple isolation methods. We also found Fusarium oxysporum, Purpureocillium lilacinum and Metarhizium anisopliae in 14%, 8% and 2% of the sites, respectively. Three abiotic variables (pH, soil organic matter and Mg) explained 96% of the variability of the entomopathogen community (EPF and entomopathogenic nematodes) in a canonical correspondence analysis, confirming the congruence of the soil properties that drive the assemblage of both entomopathogens. This study expands the knowledge of EPF distribution in natural and cultivated Mediterranean habitats.