Biological Characteristics of Beauveria majiangensis Strain MJ1015 and Optimization of Solid Medium Technology for Sporulation

The entomopathogenic fungus Beauveria majiangensis strain MJ1015, recently isolated from white grubs on a blueberry farm in Guizhou, China, could be used as a biocontrol agent. As a first step toward determining the effect of different solid culture media, temperature, and pH on colony growth rate and sporulation, we evaluated the optimum solid medium for mycelial growth and conidia production on a commercial scale. Subsequently, we also used single-factor analysis and response surface optimization to optimize the composition of the solid culture medium. On potato dextrose agar (PDA) medium, MJ1015 grew fastest and produced the highest spore yield at 29°C and pH 5. The best solid medium for the growth and sporulation of strain MJ1015 comprised 64.70 g/l of rice, 13.00 g/l of wheat, 0.30 g/l of NaNO3, 0.36 g/l of K2HPO4 · 3H2O, and 1.00 g/l of CaCO3. Rice, NaNO3, and K2HPO4 · 3H2O were the main influencing factors. The predicted value of cultured spores using the optimal medium was 4.56 x 1010 conidia/l. The validation test results showed that the average growth rate of strain MJ1015 on the optimal medium was 85% and 96% faster than that on Sabouraud dextrose agar with yeast extracts medium (SDAY) and PDA, respectively. Sporulation was 43.90 times and 9.65 times of that produced on SDAY and PDA, respectively. Our findings provide a theoretical basis for the commercial production of B. majiangensis to control white grubs.

Efficacy of Entomopathogenic Fungi as Prevention against Early Life Stages of the Red Palm Weevil, Rhynchophorus ferrugineus (Coleoptera: Curculionidae) in Laboratory and Greenhouse Trials

The red palm weevil (RPW) Rhynchophorus ferrugineus is a highly destructive invasive pest for palms whose management is mainly by application of synthetic pesticides. As a key pest of date palm plantations, it is necessary to integrate environmentally safe measures for its management. Entomopathogenic fungi (EPF) have been primarily studied as a preventative control measure due to the horizontal transfer of conidia within the RPW population. We previously demonstrated the horizontal transmission of fungal conidia from an egg-laying surface to the female weevil and then to the eggs and larvae. Based on that strategy, this study aimed to evaluate the virulence of commercial EPF products and laboratory EPF preparations to RPW females and their progeny, and their ability to protect palms against infestation. As such, it serves as a screening platform for field experiments. Mortality rates of females and eggs depended on the applied treatment formulation and fungal strain. Velifer®, a Beauveria bassiana product, and Metarhizium brunneum (Mb7) resulted in 60-88% female mortality. Mb7-as a conidial suspension or powder-resulted in 18-21% egg-hatching rates, approximately 3 times less than in the non-treated control. Treating palms with Mb7 suspension or dry formulation significantly inhibits infestation signs and results in protection. These results lay the foundation for investigating the protective rate of EPF products against RPW in date plantations.

Ecosystem services of entomopathogenic ascomycetes

Entomopathogenic ascomycetes (EA) are an important part of the microbiota in most terrestrial ecosystems, where they can be found regulating natural populations of arthropod pests in both epigeous and hypogeous habitats while also establishing unique relationships with plants. These fungi offer direct benefits to agriculture and human welfare. In the present work, we conducted a systematic review to comprehensively assess the range of ecosystem services provided by EA, including direct and indirect pest biocontrol, plant growth promotion, plant defense against other biotic and abiotic stresses, nutrient cycling, and the production of new bioactive compounds with agricultural, pharmaceutical and medical importance. Moreover, EA are compatible with the ecosystem services provided by other microbial and macrobial biocontrol agents. This systematic review identified the need for future research to focus on evaluating the economic value of the ecological services provided by EA with a special emphasis on hypocrealean fungi. This evaluation is essential not only for the conservation but also for better regulation and exploitation of the benefits of EA in promoting agricultural sustainability, reducing the use of chemicals that enter the environment, and minimizing the negative impacts of crop protection on the carbon footprint and human health.

A bacterial-like Pictet-Spenglerase drives the evolution of fungi to produce β-carboline glycosides together with separate genes

Diverse β-carboline (βC) alkaloids are produced by microbes, plants, and animals with myriad bioactivities and drug potentials. However, the biosynthetic mechanism of βCs remains largely elusive, especially regarding the hydroxyl and glucosyl modifications of βCs. Here, we report the presence of the bacterial-like Pictet-Spenglerase gene Fcs1 in the entomopathogenic Beauveria fungi that can catalyze the biosynthesis of the βC skeleton. The overexpression of Fcs1 in Beauveria bassiana led to the identification of six βC methyl glycosides, termed bassicarbosides (BCSs) A-F. We verified that the cytochrome P450 (CYP) genes adjacent to Fcs1 cannot oxidize βCs. Alternatively, the separated CYP684B2 family gene Fcs2 was identified to catalyze βC hydroxylation together with its cofactor gene Fcs3. The functional homologue of Fcs2 is only present in the Fcs1-containing fungi and highly similar to the Fcs1-connected yet nonfunctional CYP. Both evolved quicker than those from fungi without Fcs1 homologues. Finally, the paired methyl/glucosyl transferase genes were verified to mediate the production of BCSs from hydroxy-βCs. All these functionally verified genes are located on different chromosomes of Beauveria, which is in contrast to the typical content-clustered feature of fungal biosynthetic gene clusters (BGCs). We also found that the production of BCSs selectively contributed to fungal infection of different insect species. Our findings shed light on the biosynthetic mechanism of βC glycosides, including the identification of a βC hydroxylase. The results of this study also propose an evolving process of fungal BGC formation following the horizontal transfer of a bacterial gene to fungi.

Cryptic diversity and virulence of Beauveria bassiana recovered from Lycorma delicatula (spotted lanternfly) in eastern Pennsylvania

The entomopathogenic fungus Beauveria bassiana is cosmopolitan and known to infect a variety of sap-sucking pests like aphids, mealybugs, and scales in the order of Hemiptera. In Fall 2017, spotted lanternfly (SLF) adults killed by the fungal entomopathogen B. bassiana were found in Berks County, Pennsylvania. In 2018-2020 we collected SLF and nearby non-target insects killed by Beauveria spp. from 18 field sites in southeastern Pennsylvania. We identified 159 Beauveria isolates from SLF and six isolates from non-targets. Five isolates of B. bassiana and one isolate of B. brongniartii were identified from the non-targets. Based on sequence data from the nuclear B locus (Bloc) intergenic region, all the isolates from SLF were identified as B. bassiana, but there were 20 different strains within this species, grouped into two clades. Three B. bassiana strains (A, B, and L) were found in most field sites and were the most prevalent. Representative isolates for these three strains were used in laboratory bioassays and were compared to a commercial B. bassiana strain (GHA). Strain B was inferior to A, L, and GHA against nymphs; strains A and L had greater efficacy than B and GHA against adults. We also quantified conidial production on SLF cadavers. This paper discusses the diversity of these B. bassiana strains in SLF populations and implications for biological control of this abundant invasive.

Incidence of putative RNA mycoviruses in entomopathogenic fungi in Korea

Entomopathogenic fungi have potential as biocontrol agents against insect pests, and mycovirus-mediated hypervirulence may enhance their efficacy. Before initiating research on hypervirulence, the presence or absence of double-stranded (ds) RNA elements was determined in 94 Korean entomopathogenic fungi. dsRNA elements varying in size from ca. 0.8 to 7 kbp were found in 14.9% (14/94) of the strains examined, including Beauveria bassiana, Metarhizium pemphigi, M. pinghaense, M. rileyi, and Cordyceps fumosorosea. This study provides information on the incidence and electrophoretic banding patterns of dsRNA elements and is the first report of mycoviruses entomopathogenic fungi in Korea.

A comparison between the effectiveness of the fungi Beauveria bassiana and Metarhizium anisopliae for the control of Argas persicus with the emphasis of histopathological changes in the integument

Argas persicus is an important ectoparasite of domestic fowl that causes heavy economic losses to the poultry industry. The present study was carried out to compare and assess the effects induced by spraying the fungi Beauveria bassiana and Metarhizium anisopliae separately, on the mobility and viability of semifed adult A. persicus, also to follow the histopathological effect induced by a selected concentration of 10¹⁰ conidia/ml of B. bassiana on the integument. Biological studies revealed a more or less similar pattern of response in adults treated with either of the two fungi (Increasing concentration resulting in more death along with examined period). As the estimated LC50 and LC95 of B. bassiana were recorded 5 × 10⁹ and 4.6 × 10¹² conidia/ml, respectively, and for M. anisopliae were 3 × 10¹¹ and 2.7 × 10¹⁶ conidia/ml respectively, the fungus B. bassiana was more efficient than M. anisopliae when applied at the same concentrations. The study revealed that spraying of Beauveria at 10¹² conidia/ml is sufficient to control A. persicus as it recorded 100% efficacy, so it might be selected to be the effective dose. Histological investigation of the integument treated with B. bassiana revealed the dispersal of the hyphal network on the after 11 days of treatment, accompanied by other changes. Results from our study verify the susceptibility of A. persicus to the pathogenic effect induced by spraying B. bassiana, which is sufficient for its control with the recording better results.

Interspecific spread of dsRNA mycoviruses in entomogenous fungi Beauveria spp

Mycoviruses can spread interspecifically and intraspecifically in plant pathogenic fungi, as well as spreading intraspecifically in entomogenous fungi, especially Beauveria bassiana. However, whether mycoviruses are common in Beauveria spp. and can spread interspecifically between Beauveria species are unclear. Herein, four Beauveria species, but not B. bassiana, were randomly selected for double stranded RNA (dsRNA) detection. Furthermore, two previously reported dsRNA mycoviruses from B. bassiana, BbCV-2 and BbPmV-4, were used to study the interspecific transmission among B. bassiana, B. amorpha, and B. aranearum, using hyphal anastomosis and a novel insect coinfection transmission method. The results showed that dsRNA mycoviruses exist universally in Beauveria spp. and could spread interspecifically between different Beauveria species. The transmission efficiency from B. bassiana to the other two Beauveria species was significantly higher than that of the reverse transmission. Both viruses could stably and vertically spread in B. amorpha and B. aranearum, which affected their growth rate and colony morphology.

Identity, Prevalence, and Pathogenicity of Entomopathogenic Fungi Infecting Invasive Polistes (Vespidae: Polistinae) Paper Wasps in New Zealand

Two species of entomogenous fungi were discovered infecting the invasive paper wasp Polistes chinensis during an ecological study on Farewell Spit, New Zealand. We sequenced two nuclear ribosomal RDNA genes, the internal transcribed spacer (ITS) and the small ribosomal subunit 18S, and one protein-coding gene, the translation elongation factor 1-alpha (ef1 α). Combining sequence information with morphological examination, we identified these species as Beauveria malawiensis and Ophiocordyceps humbertii. We estimated that these fungi produce infection in approximately 3.3% of colonies in our study population. In bioassays, we successfully infected P. chinensis individuals from healthy colonies with B. malawiensis, with significant effects on adult mortality. This is the first record of both B. malawiensis and O. humbertii from Polistine hosts in New Zealand, and the first investigation into disease causality by these pathogens in P. chinensis. Our findings may contribute to the future development of biological control agents for paper wasps in New Zealand and elsewhere around the world.

Comparative mitogenome analysis reveals mitochondrial genome characteristics in eight strains of Beauveria

Despite the significant progress that has been made in the genome sequencing of Beauveria species, mitochondrial genome (mitogenome) used to examine genetic diversity within fungal populations. Complete mitogenomes of Beauveria species can be easily sequenced and assembled using various sequencing techniques. However, since mitogenome annotations are mainly derived from similar species comparison and software prediction, and are not supported by RNA-seq transcripts data, it leads to problems with the accuracy of mitochondrial annotations and the inability to understand RNA processing. In this study, we assembled and annotated the mitogenome of eight Beauveria strains using Illumina DNA and RNA sequencing data. The circular mitogenome of eight Beauveria strains ranged from 26,850 bp (B. caledonica strain ATCC 64970) to 35,999 bp (B. brongniartii strain GYU-BMZ03), with the intronic insertions accounting for most of the size variation, thus contributing to a total mitochondrial genome (mitogenome) size of 7.01% and 28.95%, respectively. Intron number variations were not directly related to the evolutionary relationship distance. Besides ribosomal protein S3 (rps3), most introns are lost too quickly and lack the stability of protein-coding genes. The short RNA-seq reads from next-generation sequencing can improve the mitochondrial annotation accuracy and help study polycistronic transcripts and RNA processing. The transcription initiation sites may be located in the control region. Most introns do not serve as taxonomic markers and also lack open reading frames (ORFs). We assumed that the poly A tail was added to the polycistronic transcript before splicing and one polycistronic transcript (trnM ₍₁₎-trnL ₍₁₎-trnA-trnF-trnK-trnL ₍₂₎-trnQ-trnH-trnM ₍₂₎-nad2-nad3-atp9-cox2-trnR ₍₁₎-nad4L-nad5-cob-trnC-cox1-trnR ₍₂₎-nad1-nad4-atp8-atp6-rns-trnY-trnD-trnS-trnN-cox3-trnG-nad6-trnV-trnI-trnS-trnW-trnP-rnl(rps3)-trnT-trnE-trnM ₍₃₎) was first processed from the mitogenome and was subsequently processed into smaller mono-, di-, or tricistronic RNAs.

Entomopathogenic fungi and Schinus molle essential oil: The combination of two eco-friendly agents against Aedes aegypti larvae

Aedes aegypti transmits arbovirus, which is a public health concern. Certain filamentous fungi have the potential to control the disease. Here, the effects of Metarhizium anisopliae s.l. CG 153, Beauveria bassiana s.l. CG 206 and Schinus molle L. were investigated against Aedes aegypti larvae. In addition, the effect of essential oil on fungal development was analyzed. Fungal germination was assessed after combination with essential oil at 0.0025 %, 0.0075 %, 0.005 %, or 0.01 %; all of the oil concentrations affected germination except 0.0025 % (v/v). Larvae were exposed to 0.0025 %, 0.0075 %, 0.005 %, or 0.01 % of the essential oil or Tween 80 at 0.01 %; however, only the essential oil at 0.0025 % achieved similar results as the control. Larvae were exposed to fungi at 10⁷ conidia mL^-1 alone or in combination with the essential oil at 0.0025 %. Regardless of the combination, M. anisopliae reduced the median survival time of mosquitoes more than B. bassiana. The cumulative survival of mosquitoes exposed to M. anisopliae alone or in combination with essential oil was 7.5 % and 2 %, respectively, and for B. bassiana, it was 75 % and 71 %, respectively. M. anisopliae + essential oil had a synergistic effect against larvae, whereas B. bassiana + essential oil was antagonistic. Scanning and transmission electron microscopy, and histopathology confirmed that the interaction of M. anisopliae was through the gut and hemocoel. In contrast, the mosquito's gut was the main route for invasion by B. bassiana. Results from gas chromatography studies demonstrated sabinene and bicyclogermacrene as the main compounds of S. molle, and the in-silico investigation found evidence that both compounds affect a wide range of biological activity. For the first time, we demonstrated the potential of S. molle and its interaction with both fungal strains against A. aegypti larvae. Moreover, for the first time, we reported that S. molle might be responsible for significant changes in larval physiology. This study provides new insights into host-pathogen interplay and contributes to a better understanding of pathogenesis in mosquitoes, which have significant consequences for biological control strategies.

Activity Against Musca domestica of Hypocrealean Fungi Isolated from Culicids in Central Brazil and Formulated in Vermiculite

Musca domestica L. is a cosmopolitan nuisance of high sanitary importance. Entomopathogenic fungi are innovative and attractive tools for integrated control of the housefly to overcome insufficient levels of control caused by increasing resistance of this pest against chemical insecticides. High virulence of a fungal strain is a prerequisite to develop a mycoinsecticide, and the present study investigated the potential of hypocrealean fungi from the genera Beauveria, Clonostachys, Cordyceps, Akanthomyces, Metarhizium, and Tolypocladium, isolated from mosquitoes in Central Brazil against M. domestica. The highest mortalities (larvae, pupae, and adults) were caused by Metarhizium humberi IP 478 (98%) and IP 421 (90%), Metarhizium anisopliae IP 432 (85%), Beauveria bassiana IP 433 (82%), and Tolypocladium cylindrosporum IP 425 (68%) after a 23-day exposure of initially pre-pupating third instar larvae to conidia mixed with vermiculite. Lethal concentrations to kill 90% of adults of IP 433 and IP 478 were 5 × 10⁷ and 10⁸ conidia g^-1 substrate, respectively. Fifty percent of adults were killed within 4 to 5 days of exposure initially as pupae close to emergence to substrate treated with conidia of IP 478 or IP 433 at 1.1 × 10⁸ conidia g^-1, respectively. The other fungal strains tested were less virulent. The results demonstrate high potentials for conidial preparations in vermiculite of IP 433 and IP 478 as candidates for the biological control of both pre-pupating larvae, pupae, and emerging adults of houseflies.

Characterization and bio-efficacy of entomopathogenic Beauveria associated with cuticle-degrading enzymes to restrain sucking pest Bemisia tabaci

The entomopathogenic Beauveria spp. were acquired from insect cadavers and soil rhizosphere of cotton, groundnut, and castor. Among Beauveria, five spp. derived from infected insects, eight Beauveria found from soil, and one strain of Beauveria bassiana collected from MTCC 9544. Beauveria were characterized for morphology and cuticle-degrading enzyme activity associated with virulence against Bemisia tabaci. The colony morphology, conidial arrangement, size, and shape confirmed all isolates as Beauveria. The chitinase (EC 3.2.1.14) and lipase (EC 3.1.1.3) activities were observed the highest in Beauveria JAU2, while higher protease (EC 3.4.21.4) activity found in JAU4 followed by JAU2 at 240 h. The bio-efficacy of Beauveria (1 × 10⁷ conidia.ml^-1) illustrated that potent JAU2 was examined with the highest % mortality and corrected mortality of B. tabaci at 144 h followed by JAU1. The LC₉₀ and LC₅₀were determined from potent (JAU1 and JAU2) and weak (JAU6), and it was found the lowest in JAU2. The most potent Beauveria JAU2, isolated from insect cadaver (Harmivora armigera), was illustrated higher virulence than other isolates. The Beauveria JAU2 were recognized as Beauveria bassiana based on the shape of conidia and size (2.00 to 2.09 µm dia) as examined in SEM. Study insight into recognition of potent Beauveria bassiana JAU2 was linked with cuticle-degrading enzyme activity for insecticidal action. The JAU2 isolate established the most positive correlation (P_0.01: 0.864) between chitinase activity and corrected mortality of insect.

Potential use of beneficial fungal microorganisms and C-phycocyanin extract for enhancing seed germination, seedling growth and biochemical traits of Solanum lycopersicum L

Background

Biopriming as a new technique of seed treatment involves the application of beneficial microorganisms on the seed surface to stimulate seed germination, plant growth, and protect the seed from soil and seed-borne pathogens. The present investigation was carried out on seed germination, seedling vigor and biochemical traits of one of the most important vegetable crops (Tomato, Solanum lycopersicum L.). The treatments comprised viz. T1: Non primed seeds (Control), T2: Hydropriming, T3: Biopriming with C-phycocyanin (C-PC) (Spirulina platensis extract), T4: Biopriming with Trichoderma asperellum, T5: Biopriming with T. viride, T6: Biopriming with Beauveria bassiana.

Results

Extraction and purification of C-phycocyanin (C-PC) from the dry S. platensis powder using various methods was performed. The purity after dialyses was 0.49 and its ultimate purity (A₆₂₀/A₂₈₀) after ion-exchange chromatography was 4.64. The results on tomato seedlings revealed that the maximum germination percentage (100%), germination index (15.46 and 15.12), seedling length (10.67 cm), seedling dry weight (1.73 and 1.97 mg) and seedling length vigor index (1066.7) were recorded for tomato biopriming with T. viride, and B. bassiana (T5 and T6). Moreover, the quantitative estimation of total carbohydrates and total free amino acids contents in bioprimed tomato seedlings indicated a significantly higher amount with T. viride, followed by those bioprimed with T. asperellum, B. bassiana and C-PC extract.

Conclusion

Thus, our results indicated that biopriming of tomato seeds with beneficial fungal inoculants and C-PC was very effective. The most operative biostimulants were those bioprimed with T. viride and B. bassiana compared to other biostimulants (T. asperellum and C-PC). Therefore, to ensure sustainable agriculture, this study offers new possibilities for the biopriming application as an alternative and ecological management strategy to chemical treatment and provides a valuable basis for improving seed germination.

Exploring interactions between Beauveria and Metarhizium strains through co-inoculation and responses of perennial ryegrass in a one-year trial

Perennial ryegrass (Lolium perenne L.) possesses a high level of nutritional quality and is widely used as a forage species to establish permanent pastures in southern Chile. However, the productivity of most such pastures is limited by various environmental agents, such as insect pests and drought. In this context, our work stresses the need for elucidating the ability of fungal endophytes to establish interactions with plants, and to understand how these processes contribute to plant performance and fitness. Therefore, we evaluated the colonization and impact of two native strains of the endophytic insect-pathogenic fungus (EIPF) group isolated from permanent ryegrass pastures in southern Chile. Roots and seeds of ryegrass and scarabaeid larvae were collected from nine different ryegrass pastures in the Los Ríos region of southern Chile to specifically isolate EIPFs belonging to the genera Beauveria and Metarhizium. Fungal isolations were made on 2% water agar with antibiotics, and strains were identified by analyzing the entire internal transcribed spacer (ITS) 1-5.8S-ITS2 ribosomal DNA region. Four strains of Beauveria and 33 strains of Metarhizium were isolated only in scarabaeid larvae from ryegrass pastures across four sites. Experimental mini-pastures that were either not inoculated (control) or co-inoculated with conidia of the strains Beauveria vermiconia NRRL B-67993 (P55_1) and Metarhizium aff. lepidiotae NRRL B-67994 (M25_2) under two soil humidity levels were used. Ryegrass plants were randomly collected from the mini-pastures to characterize EIPF colonization in the roots by real-time PCR and fluorescence microscopy. Aboveground biomass was measured to analyze the putative impact of colonization on the mini-pastures' aboveground phenotypic traits with R software using a linear mixed-effects model and the ANOVA statistical test. Seasonal variation in the relative abundance of EIPFs was observed, which was similar between both strains from autumn to spring, but different in summer. In summer, the relative abundance of both EIPFs decreased under normal moisture conditions, but it did not differ significantly under water stress. The aboveground biomass of ryegrass also increased from autumn to spring and decreased in summer in both the inoculated and control mini-pastures. Although differences were observed between moisture levels, they were not significant between the control and inoculated mini-pastures, except in July (fresh weight and leaf area) and October (dry weight). Our findings indicate that native strains of B. vermiconia NRRL B-67993 (P55_1) and M. aff. lepidiotae NRRL B-67994 (M25_2) colonize and co-exist in the roots of ryegrass, and these had little or no effect on the mini-pastures' aboveground biomass; however, they could have other functions, such as protection against root herbivory by insect pests.

bassiana species complexes with whole-genome sequencing, morphometric and chemical analyses

Fungi are rich in complexes of cryptic species that need a combination of different approaches to be delimited, including genomic information. Beauveria (Cordycipitaceae, Hypocreales) is a well-known genus of entomopathogenic fungi, used as a biocontrol agent. In this study we present a polyphasic taxonomy regarding two widely distributed complexes of Beauveria: B. asiatica and B. bassiana s.lat. Some of the genetic groups as previously detected within both taxa were either confirmed or fused using population genomics. High levels of divergence were found between two clades in B. asiatica and among three clades in B. bassiana, supporting their subdivision as distinct species. Morphological examination focusing on the width and the length of phialides and conidia showed no difference among the clades within B. bassiana while conidial length was significantly different among clades within B. asiatica. The secondary metabolite profiles obtained by liquid chromatography-mass spectrometry (LC-MS) allowed a distinction between B. asiatica and B. bassiana, but not between the clades therein. Based on these genomic, morphological, chemical data, we proposed a clade of B. asiatica as a new species, named B. thailandica, and two clades of B. bassiana to respectively represent B. namnaoensis and B. neobassiana spp. nov. Such closely related but divergent species with different host ranges have potential to elucidate the evolution of host specificity, with potential biocontrol application. Citation: Kobmoo N, Arnamnart N, Pootakham W, et al. 2021. The integrative taxonomy of Beauveria asiatica and B. bassiana species complexes with whole-genome sequencing, morphometric and chemical analyses. Persoonia 47: 136-150. https://doi.org/10.3767/persoonia.2021.47.04.

Efficacy of the Applied Natural Enemies on the Survival of Colorado Potato Beetle Adults

Simple Summary

Colorado potato beetle (CPB) Leptinotarsa decemlineata is the potato plant’s most destructive pest. Recently, resistance to the traditional insecticides has appeared, thus new environmentally friendly control agents are highly needed. In our study, we searched for the most effective entomopathogenic agents that could be used to decrease the emergence of CPB adults from the soil. We selected two entomopathogenic nematodes (Steinernema carpocapsae and S. feltiae) and one strain of fungus (Beauveria bassiana). The suspension application was done on the leaves, plus by watering the pods and the field plots. All the treatments had an obvious effect, but in the field, only the fungal treatment showed a promising result. Further research is needed to develop the most effective application for field usage.

Abstract

Colorado potato beetle Leptinotarsa decemlineata is among the most destructive pests of potatoes quickly developing resistance to traditional insecticides. In the present study, we tested the effect of various species and strains of entomopathogenic nematodes on CPB adults, and subsequently, the most effective nematodes were applied alone and in combination with entomopathogenic fungus B. bassiana in pots with potato plants and in the field and their effect on the number of emerging adults was evaluated. In the experimental infections, both the nematode invasion and pathogenicity were variable, and, in several strains, the mortality reached 100%. In pot experiments, soil application of nematodes S. carpocapsae 1343 and S. feltiae Jakub and fungus significantly decreased numbers of emerging CPB adults, while, after the application on leaves, only fungal treatment was effective. The field application of fungus B. bassiana significantly decreased the number of emerging CPB adults in comparison to control sites by ca. 30% while the effect of nematodes and the nematodes–fungus combination was not significant. In conclusion, we demonstrate the necessity of thorough bioassays to select the most effective nematode strains. Entomopathogenic nematodes have the potential to effectively decrease the emergence of CPB adults, but further research is needed to improve the effectiveness in the field.

bassiana species complexes with whole-genome sequencing, morphometric and chemical analyses

Fungi are rich in complexes of cryptic species that need a combination of different approaches to be delimited, including genomic information. Beauveria (Cordycipitaceae, Hypocreales) is a well-known genus of entomopathogenic fungi, used as a biocontrol agent. In this study we present a polyphasic taxonomy regarding two widely distributed complexes of Beauveria: B. asiatica and B. bassiana s.lat. Some of the genetic groups as previously detected within both taxa were either confirmed or fused using population genomics. High levels of divergence were found between two clades in B. asiatica and among three clades in B. bassiana, supporting their subdivision as distinct species. Morphological examination focusing on the width and the length of phialides and conidia showed no difference among the clades within B. bassiana while conidial length was significantly different among clades within B. asiatica. The secondary metabolite profiles obtained by liquid chromatography-mass spectrometry (LC-MS) allowed a distinction between B. asiatica and B. bassiana, but not between the clades therein. Based on these genomic, morphological, chemical data, we proposed a clade of B. asiatica as a new species, named B. thailandica, and two clades of B. bassiana to respectively represent B. namnaoensis and B. neobassiana spp. nov. Such closely related but divergent species with different host ranges have potential to elucidate the evolution of host specificity, with potential biocontrol application. Citation: Kobmoo N, Arnamnart N, Pootakham W, et al. 2021. The integrative taxonomy of Beauveria asiatica and B. bassiana species complexes with whole-genome sequencing, morphometric and chemical analyses. Persoonia 47: 136-150. https://doi.org/10.3767/persoonia.2021.47.04.

Metabolomics of extracellular compounds and parasitic enzymes of Beauveria bassiana associated with biological control of whiteflies (Bemisia tabaci)

The Beauveria spp. were isolated from soil and insect cadavers of crop rhizosphere and characterized for parasitic enzyme activity and virulence against whiteflies (Bemisia tabaci). The colony morphology and molecular identification using ITS specific marker were carried out and confirmed entomopathogenic fungi as Beauveria bassiana. The bioefficacy of B. bassiana against whiteflies demonstrated highest corrected mortality and lowest LC₅₀ in isolate B. bassiana JAU2 (SEM morphology) followed by JAU1 on 6th days. Parasitic enzymes chitinase and lipase were determined highest in JAU2 and protease activity examined higher in isolate JAU4 followed by JAU2 isolate on 6th days after inoculation. Comparative extracellular metabolomics carried out from potent (JAU1 and JAU2), moderate (JAU4 and JAU14) and weak (JAU6) B. bassiana isolates in normal suborder dextrose agar with yeast extrect (SDAY) and chitin induced media. Results illustrated that total 105 metabolites identified common for all five B. bassiana isolates differing in virulence. However, the color intensity of the metabolites changes in heat map showing differential concentration of that extracellular compound compared to other isolates. The volcano plot analysis illustrated 58 compounds significanlty diverse between potent JAU1 and JAU2 under two different culture conditions of which 34 compounds recognized up regulated in most potent JAU2 under chitin induced media. Out of 34 metabolites, ten compounds viz., fumaricine, resazurin, N-methyldioctylamine, penaresidun B, tetralin, squamocin B, oligomycin C, pubesenolide, epirbuterol and gentamicin C1a were recognized significantly upregulated in most potent JAU2 and reported for antimicrobial, nematicidal, larvicidalor insecticidal activities. The mass spectra and fragment structure were elucidated under LCMS-QTOF for some novel and unique compounds recognized in most potent B. bassiana JAU2, involved in parasitic activity against whiteflies.

Distribution and Diversity of Beauveria in Boreal Forests of Northern European Russia

The distribution and genetic diversity of 91 of Beauveria isolates collected during a long-term survey in boreal forests of northern European Russia was studied. Based on morphological and sequence analysis of TEF and Bloc loci, three Beauveria spp. were identified: B. pseudobassiana, B. bassiana, and B. caledonica, with abundance of 81, 11, and 8%, respectively. Through multilocus sequencing, four haplotypes of B. bassiana and two haplotypes of B. caledonica were detected. Twelve haplotypes of B. pseudobassiana with non-random distribution were identified. Two haplotypes of B. pseudobassiana were the most abundant and widespread occurring across the whole study area, whereas others tended to be more specific to either the north or south of the study area, indicating the presence of different subpopulations. For further analysis of these putative subpopulations, southern and northern areas were separated along the boundary of the Köppen-Geiger climate zones (dfb and dfc), and the genetic structure was examined by analysis of molecular variance and spatial autocorrelation. Molecular evidence of intraspecific recombination of B. pseudobassiana and B. bassiana across northern European Russia area was indicated.

Entomopathogenic Fungi for Tick Control in Cattle Livestock From Mexico

Ticks are one of the main economic threats to the cattle industry worldwide affecting productivity, health and welfare. The need for alternative methods to control tick populations is prompted by the high prevalence of multiresistant tick strains to the main chemical acaricides and their ecological consequences. Biological control using entomopathogenic fungi (EPF) is one of the most promising alternative options. The objective of this paper is to review the use of EPF as an alternative control method against cattle ticks in Mexico. Metarhizium anisopliae sensu lato (s.l.) and Beauveria bassiana s.l. are the most studied EPF for the biological control of ticks in the laboratory and in the field, mainly against Rhipicephalus microplus; however, evaluations against other important cattle ticks such as Amblyomma mixtum and R. annulatus, are needed. A transdisciplinary approach is required to incorporate different types of tools, such as genomics, transcriptomics and proteomics in order to better understand the pathogenicity/virulence mechanism in EPF against ticks. Laboratory tests have demonstrated the EPF efficacy to control susceptible and resistant/multiresistant tick populations; whereas, field tests have shown satisfactory control efficiency of M. anisopliae s.l. against different stages of R. microplus when applied both on pasture and on cattle. Epidemiological aspects of ticks and environmental factors are considered as components that influence the acaricidal behavior of the EPF. Finally, considering all these aspects, some recommendations are proposed for the use of EPF in integrated control schemes for livestock ticks.

Simple method to detect and to isolate entomopathogenic fungi (Hypocreales) from mosquito larvae

Entomopathogenic fungi are important agents for mosquito vector control. We report on the utility of a simple method to detect fungi on living larvae of Aedes aegypti that had been exposed to a fungal entomopathogen. Four species of the hypocrealean genera Metarhizium, Beauveria, Tolypocladium and Culicinomyces, known for their larvicidal activity against mosquito species, were tested. Living larvae previously exposed to a suspension of different conidial concentrations were set directly into the surface water film on non-nutritive agar supplemented with chloramphenicol, thiabendazole and crystal violet and then incubated. Except for C. clavisporus ARSEF 964 (which developed and produced conidia mostly inside the cadaver rather than on its surface in the present study), this method favored external fungal development and conidiogenesis on larvae of different instars after death. The dead larva on the water agar represents the unique and specific source of nutrition for the fungus that killed it. The technique facilitates the detection and posterior isolation of entomopathogenic fungi, and offers a compact, convenient, and rapid means to survey larval mosquito populations for fungal pathogens at the field.

The complete mitochondrial genome of Beauveria lii (Hypocreales: Cordycipitaceae)

The mitochondrial genome of Beauveria lii, strain RCEF500, was sequenced on the NovaSeq 6000 and the Nanopore Sequencer, and annotated. The genome is 59,014 bp in length, encoding 15 conserved protein-coding genes (PCGs), 2 rRNA genes and 23 tRNA genes. The nucleotide composition of Beauveria lii mitochondrial genome was 38.23% of A, 35.81% of T, 11.61% of C, 14.36% of G, 25.97% of G + C content. Phylogenetic analysis confirmed B. lii as a member of Beauveria (Cordycipitaceae). The mitochondrial genome of B. lii will contribute to the understanding of phylogeny and evolution of the genus and family.

Abundance of Entomopathogenic Fungi in Leaf Litter and Soil Layers in Forested Habitats in Poland

This study aims to determine the species composition and density of colony-forming units (CFU) of entomopathogenic fungi (EPF) in leaf litter at different depths of the top layer of forest soils depending on the type of forest (coniferous, deciduous and mixed forest), and the date of sampling (spring, autumn). In each type of forest, leaf litter and soil were collected using a soil stick from four depths of soil: 0-5, 5-10, 10-15 and 15-20 cm. Entomopathogenic fungi were isolated by a soil or litter dilution plating method on a selective medium. Four fungal genera were found: Beauveria spp., Cordyceps spp., Metarhizium spp., and Lecanicillium spp. The density of EPF was usually higher in leaf litter than in the layers of soil below, and the most frequently isolated species from both environments were Beauveria spp. among soil samples from all forest types; Beauveria spp. were most abundant in the top layer (0-5 cm), and their density of CFUs gradually decreased deeper into the soil profile.

Effect of Soil Chemical Properties on the Occurrence and Distribution of Entomopathogenic Fungi in Portuguese Grapevine Fields

Entomopathogenic fungi (EPF) contribute to different ecosystem services. However, factors affecting their natural occurrences in soil remain poorly understood. In a previous study, 81 soil samples were subjected to insect baiting using Galleria mellonella and Tenebrio molitor to isolate EPF from Portuguese vine farms. Here, soils yielding any of the four common EPF, i.e., Beauveria bassiana, Purpureocillium lilacinum, Metarhizium robertsii, and Clonostachys rosea f. rosea, were correlated with their chemical properties. Beauveria bassiana was negatively affected by higher available P (p = 0.02), exchangeable K-ions (p = 0.016) and positively affected by higher soil pH_H₂O (p = 0.021). High exchangeable K-ions inhibited P. lilacinum (p = 0.011) and promoted C. rosea f. rosea (p = 0.03). Moreover, high available K also suppressed P. lilacinum (p = 0.027). Metarhizium robertsii was inhibited by higher organic matter content (p = 0.009), higher C:N (p = 0.017), total N (p = 0.007), and exchangeable Mg-ions (p = 0.026), and promoted by higher exchangeable Na-ions (p = 0.003). Nonetheless, mean comparisons and principal component analysis suggested that higher soil pH and exchangeable Ca-ions have contrasting effects on EPF occurrences, as they promote B. bassiana and inhibit M. robertsii. Herbicides did not seem to affect EPF presence. Overall, this study is among the first reports on the effects of soil chemistry on EPF other than Metarhizium, and will facilitate biological pest management approaches.

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.

Mitochondrial evolution in the entomopathogenic fungal genus Beauveria

Species in the fungal genus Beauveria are pathogens of invertebrates and have been commonly used as the active agent in biopesticides. After many decades with few species described, recent molecular approaches to classification have led to over 25 species now delimited. Little attention has been given to the mitochondrial genomes of Beauveria but better understanding may led to insights into the nature of species and evolution in this important genus. In this study, we sequenced the mitochondrial genomes of four new strains belonging to Beauveria bassiana, Beauveria caledonica and Beauveria malawiensis, and compared them to existing mitochondrial sequences of related fungi. The mitochondrial genomes of Beauveria ranged widely from 28,806 to 44,135 base pairs, with intron insertions accounting for most size variation and up to 39% (B. malawiensis) of the mitochondrial length due to introns in genes. Gene order of the common mitochondrial genes did not vary among the Beauveria sequences, but variation was observed in the number of transfer ribonucleic acid genes. Although phylogenetic analysis using whole mitochondrial genomes showed, unsurprisingly, that B. bassiana isolates were the most closely related to each other, mitochondrial codon usage suggested that some B. bassiana isolates were more similar to B. malawiensis and B. caledonica than the other B. bassiana isolates analyzed.

Integration of Entomopathogenic Fungi into IPM Programs: Studies Involving Weevils (Coleoptera: Curculionoidea) Affecting Horticultural Crops

Weevils are significant pests of horticultural crops and are largely managed with insecticides. In response to concerns about negative impacts of synthetic insecticides on humans and the environment, entomopathogenic fungi (EPF) have been developed as an alternative method of control, and as such appear to be "ready-made" components of integrated pest management (IPM) programs. As the success of pest control requires a thorough knowledge of the biology of the pests, this review summarises our current knowledge of weevil biology on nut trees, fruit crops, plant storage roots, and palm trees. In addition, three groups of life cycles are defined based on weevil developmental habitats, and together with information from studies of EPF activity on these groups, we discuss the tactics for integrating EPF into IPM programs. Finally, we highlight the gaps in the research required to optimise the performance of EPF and provide recommendations for the improvement of EPF efficacy for the management of key weevils of horticultural crops.

Ultrastructural changes induced by the entomopathogenic fungus Beauveria bassiana in the ovary of the tick Argas (Persicargas) persicus (Oken)

The present study was carried out to assess the effects on the ovary of fed female Argas persicus following spraying of the ticks with spores of the fungus Beauveria bassiana suspended in triton X100 at a concentration of 10⁷ conidia/mL. Scanning and transmission electron microscopy observations provided evidence that B. bassiana invaded the ovary, causing extensive morphological damage and deterioration of the developing oocytes. Destruction of the shape and internal organelles of young and previtellogenic oocytes and complete inhibition of vitellogenesis was evident. This histopathological study is the first demonstration of ultrastructural damage in the ovaries of A. persicus after infection with B. bassiana. The data presented confirm that B. bassiana affects the ovary either directly by entering the oocytes and/or indirectly by producing toxins in the haemolymph that interfere with the development of oocytes, thus potentially contributing to the control of this tick in a way that is safe for its host and the environment.

Response of the macadamia seed weevil Kuschelorhynchus macadamiae (Coleoptera: Curculionidae) to Metarhizium anisopliae and Beauveria bassiana in laboratory bioassays

Macadamia seed weevil, Kuschelorhynchus macadamiae Jennings and Oberprieler, is a major pest of macadamia in eastern Australia, causing yield losses of up to 15%. Current control methods involve two applications of acephate per season but more recently have moved to a single application of indoxacarb, combined with the collection and destruction of fallen nuts that contain developing larvae. As a first step towards reducing the dependence of the industry on synthetic insecticides, we tested six isolates of M. anisopliae, six isolates of B. bassiana and one commercial B. bassiana product (Velifer® biological insecticide) against adult macadamia seed weevil under laboratory conditions. All isolates were pathogenic against adult weevils with M. anisopliae accession ECS1/BRIP 70272 and B. bassiana accession B27/BRIP 70267 causing 97.5% and 92.5% mortality 12 days after being treated at 1 × 10⁷ conidia/mL. Isolates ECS1/BRIP 70272 and B27/BRIP 70267 had the shortest LT₅₀ values of 5.13 days and 5.37 days respectively. The median lethal concentrations (LC₅₀) for ECS1/BRIP 70272 and B27/BRIP 70267 were 1.48 × 10⁵ and 1.65 × 10⁵ conidia/mL respectively. Results of this study indicate that M. anisopliae accession ECS1/BRIP 70272 and B. bassiana accession B27/BRIP 70267 have considerable potential for K. macadamiae control, and should be developed into biological insecticides for integration into macadamia pest management programs.

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.

Differential susceptibility of blastospores and aerial conidia of entomopathogenic fungi to heat and UV-B stresses

We investigated the comparative susceptibility to heat and UV-B radiation of blastospores and aerial conidia of Metarhizium spp. (Metarhizium robertsii IP 146, Metarhizium anisopliae s.l. IP 363 and Metarhizium acridum ARSEF 324) and Beauveria bassiana s.l. (IP 361 and CG 307). Conidia and blastospores were produced in solid or liquid Adámek-modified medium, respectively, and then exposed to heat (45 ± 0.2 °C) in a range of 0 (control) to 360 min; the susceptibility of fungal propagules to heat exposures was assessed to express relative viability. Similarly, both propagules of each isolate were also exposed to a range of 0 (control) to 8.1 kJ m^-2 under artificial UV-B radiation. Our results showed that fungal isolates, propagule types and exposure time or dose of the stressor source play critical roles in fungal survival challenged with UV-B and heat. Conidia of ARSEF 324, IP 363, IP 146 and IP 361 exposed to heat survived significantly longer than their blastospores, except for blastospores of CG 307. Conidia and blastospores of IP 146 and IP 363 were equally tolerant to UV-B radiation. We claim that blastospores of certain isolates may be promising candidates to control arthropod pests in regions where heat and UV-B are limiting environmental factors.

Three-dimensional cellular aggregates formed by Beauveria pseudobassiana in liquid culture with potential for use as a biocontrol agent of the African black beetle (Heteronychus arator)

Beauveria pseudobassiana formed three-dimensional aggregates of cells (CAs) in liquid culture. CAs were formed mainly by blastospores and conidia, distinct from microsclerotia formed through adhesion of hyphae. The formation, germination and sporulation of CAs were studied, as well as the pathogenicity of conidia produced from them against adults of black beetle. After 4 days of culture, CAs were formed, becoming compact and melanised after 10 days of incubation. Electron microscopy showed three-dimensional CAs averaging 431.65 µm in length with irregular shapes and rough surfaces, where cells were trapped within an extracellular matrix. CAs germinated after 2 days of incubation on agar-plates producing hyphae and forming phialides and conidia after 4 days. Produced conidia caused 45% mortality of black beetle adults. CAs germination and sporulation on soil were directly correlated with soil moisture, reaching 80% and 100% germination on the surface of soil with 17% and 30% moisture, respectively. CAs maintained 100% germination after 2 years of storage under refrigeration. These CAs could have a similar function as microsclerotia in nature, acting as resistant structures able to protect internal cells and their ability to sporulate producing infective conidia, suggesting their potential to be used as bioinsecticides to control soil-dwelling insects.

Soil drenching with entomopathogenic fungi for control of the soil-dwelling life stages and adults of the same generation of Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae)

Four Beauveria bassiana and three Metarhizium brunneum isolates were evaluated, as soil drenches, against Spodoptera littoralis prepupae. Treatment efficacy was determined by assessing total mortality during development from prepupae through to pupae and adults; mortality and sub-lethal effects on reproduction were also quantified for adults emerging from surviving prepupae/pupae. All isolates were pathogenic but overall mortality varied between 31.7 and 83.3% (0% for control); average survival time was 7.5-10.5 days (14.0 days for control). From 1.7-15.0% of adults emerging from surviving prepupae/pupae were deformed (0% in control). Contact with fungal suspensions as prepupae/pupae caused a significant reduction in fecundity of emerging adult females (15-58.9%), and a significant reduction in egg viability (6.8-28.4%) compared with controls. Two isolates were selected for virulence evaluation against S. littoralis prepupae. The LC50s were 1.7 × 107 and 1.8 × 107 conidia ml-1 and the median survival times were 7 and 6 days for isolates EAMa 01/58-Su and EAMb 09/01-Su, respectively. Destruxin A was present in pupae developing from prepupae treated with isolates EAMa 01/58-Su (0.010 ± 0.002 µg pupae-1) and EAMb 09/01-Su (0.015 ± 0.003 µg pupae-1). The use of entomopathogenic fungi as soil drenches could be a key component of S. littoralis IPM strategies due to direct reductions in the number of soil-dwelling life stages and, also, the significant reduction in reproductive potential of surviving adults.

Morphology, molecular characterization, and virulence of Beauveria pseudobassiana isolated from different hosts

Beauveria pseudobassiana has great potential for use in the management of various insect pests. In the present study, we aimed to explore the the virulence of B. pseudobassiana isolated from a diversity of hosts to Bombyx mori and Tenebrio molitor larvae. To this end, 15B. pseudobassiana isolates from 10 different geographical locations were identified based on morphological characteristics and molecular data. The phylogenetic positions of the isolates were evaluated according to morphological features and phylogenetic inferences based on six loci (nrSSU, nrLSU, TEF, RPB1, RPB2 and Bloc). In addition to growth in soil, the B. pseudobassiana isolates in our study were isolated from a wide host range that extended to 5 orders, 11 families, and 14 species. Moreover, anamorphically typified B. pseudobassiana was grown for the first time from teleomorph stromata. Pathogenicity of the B. pseudobassiana isolates from the different hosts was determined with two bioassays using B. mori and T. molitor larvae. The results indicated that mortality of B. mori caused by the lepidopteran isolates was significantly higher than that of isolates from other hosts, and virulence of the coleopteran isolates to T. molitor was significantly higher than that of isolates from other hosts. The host specificity of B. pseudobassiana should be studied in more detail before future consideration of isolates for use in biological control of pests.

Root colonization by endophytic insect-pathogenic fungi

Several ascomycetous insect-pathogenic fungi, including species in the genera Beauveria and Metarhizium, are plant root symbionts/endophytes and are termed as endophytic insect-pathogenic fungi (EIPF). The endophytic capability and insect pathogenicity of Metarhizium are coupled to provide an active method of insect-derived nitrogen transfer to plant hosts via fungal mycelia. In exchange for the insect-derived nitrogen, the plant provides photosynthate to the fungus. This symbiotic interaction offers other benefits to the plant-EIPF can improve plant growth, they are antagonistic to plant pathogens and herbivores and can enhance the plant tolerance to abiotic stresses. The mechanisms and underlying biochemical and genetic features of insect pathogenesis are generally well-established. However, there is a paucity of information regarding the underlying mechanisms in this plant-symbiotic association. Here we review five aspects of EIPF interactions with host plant roots: (i) rhizosphere colonization, (ii) signalling factors from the plant and EIPF, (iii) modulation of plant defence responses, (iv) nutrient exchange and (v) tripartite interactions with insects and other micro-organisms. The elucidation of these interactions is fundamental to understanding this symbiotic association for effective application of EIPF in an agricultural setting.

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The genus Beauveria is considered a cosmopolitan anamorphic and teleomorphic genus of soilborne necrotrophic arthropod-pathogenic fungi that includes ecologically and economically important species. Species identification in Beauveria is difficult because of its structural simplicity and the lack of distinctive phenotypic variation. Therefore, the use of multi-locus sequence data is essential to establish robust species boundaries in addition to DNA-based species delimitation methods using genetic distance, coalescent, and genealogical concordance approaches (polyphasic approaches). In this regard, our study used multilocus phylogeny and five DNA-based methods to delimit species in Beauveria using three molecular makers. These polyphasic analyses allowed for the delimitation of 20-28 species in Beauveria, confirming cryptic diversity in five species (i.e. B. amorpha, B. bassiana, B. diapheromeriphila, and B. pseudobassiana) and supporting the description of B. peruviensis as a new taxon from northeastern Peru. The other five species were not evaluated as they did not have enough data (i.e. B. araneola, B. gryllotalpidicola, B. loeiensis, B. medogensis, and B. rudraprayagi). Our results demonstrate that the congruence among different methods in a polyphasic approach (e.g. genetic distance and coalescence methods) is more likely to show reliably supported species boundaries. Among the methods applied in this study, genetic distance, coalescent approaches, and multilocus phylogeny are crucial when establishing species boundaries in Beauveria.

Non-Entomopathogenic Roles of Entomopathogenic Fungi in Promoting Plant Health and Growth

Multiple genera of hypocrealean fungi infect and kill a wide variety of arthropod pests. Several formulations based on these soilborne fungi are commercially available as biopesticides for controlling urban, garden, greenhouse, and agricultural pests. These fungi are an important part of integrated pest management strategies to maintain pest control efficacy, reduce the risk of chemical insecticide resistance, and offer environmentally sustainable pest suppression. While the entomopathogenic or pest management role of these fungi is well documented, several studies in the past decade or two have provided insights into their relationship with plants, soil, and plant pathogens, and their additional roles in promoting plant growth and health. This review highlights these endophytic, mycorrhiza-like, and disease-antagonizing roles of entomopathogenic fungi.

Foraging Macrotermes natalensis Fungus-Growing Termites Avoid a Mycopathogen but Not an Entomopathogen

Fungus-growing termites have to defend both themselves and their monoculture fungal cultivars from antagonistic microbes. One of the ways that pathogens can enter the termite colony is on the plant substrate that is collected by termite foragers. In order to understand whether foragers avoid substrate infected with antagonists, we offered sub-colonies of Macrotermes natalensis a choice between food exposed to either a mycopathogenic or an entomopathogenic fungus, and control food. Workers did not show any preference between entomopathogen-exposed and control substrate, but significantly avoided the mycopathogen-exposed substrate. This suggests that the behaviour of foraging workers is more strongly influenced by pathogens affecting their crop than those posing risks to the termite workers themselves.

The use of fungal entomopathogens as endophytes in biological control: a review

Fungal entomopathogens have been proposed as environmentally friendly alternatives to chemical control. Unfortunately, their effectiveness continues to be limited by their susceptibility to ultraviolet (UV) light and low moisture. A relatively recent development, the use of fungal entomopathogens as endophytes, might overcome the traditional obstacles impeding the widespread adoption of fungal entomopathogens and also provide a novel alternative for management of insect pests and plant pathogens. In addition, some fungal entomopathogens could also function as biofertilizers. Eighty-five papers covering 109 individual fungal entomopathogen studies involving 12 species in six genera are reviewed. Thirty-eight plant species in 19 families were studied, with maize, common bean, and tomato being the most investigated. Of the 85 papers, 39 (46%) examined the effects of fungal entomopathogen endophytism on 33 insect species in 17 families and eight orders. Thirty-four (40%) examined plant response to endophytism, corresponding to 20 plant species. Various inoculation techniques (e.g., foliar sprays, soil drenching, seed soaking, injections, etc.) are effective in introducing fungal entomopathogens as endophytes, but colonization appears to be localized and ephemeral. The field of insect pathology will not substantially profit from dozens of additional studies attempting to introduce fungal entomopathogens into a wider array of plants, without attempting to understand the mechanisms underlying endophytism, the responses of the plant to such endophytism, and the consequent responses of insect pests and plant pathogens. This review presents several areas that should receive focused attention to increase the probability of success for making this technology an effective alternative to chemical control.

Root environment is a key determinant of fungal entomopathogen endophytism following seed treatment in the common bean, Phaseolus vulgaris

The common bean is the most important food legume in the world. We examined the potential of the fungal entomopathogens Beauveria bassiana and Metarhizium anisopliae applied as seed treatments for their endophytic establishment in the common bean. Endophytic colonization in sterile sand:peat averaged ca. 40% higher for fungus treatments and ca. six times higher for volunteer fungi (other fungal endophytes naturally occurring in our samples), relative to sterile vermiculite. Colonization by B. bassiana and M. anisopliae was least variable in sterile vermiculite and most variable in sterile soil:sand:peat. The impact of soil sterilization on endophytic colonization was assessed in a separate experiment using six different field-collected soils. Soil sterilization was the variable with the largest impact on colonization (70.8% of its total variance), while the fungal isolate used to inoculate seeds explained 8.4% of the variance. Under natural microbial soil conditions experienced by common bean farmers, seed inoculations with B. bassiana and M. anisopliae are unlikely to yield predictable levels of endophytic colonization.

A phylogenetically-based nomenclature for Cordycipitaceae (Hypocreales)

The ending of dual nomenclatural systems for pleomorphic fungi in 2011 requires the reconciliation of competing names, ideally linked through culture based or molecular methods. The phylogenetic systematics of Hypocreales and its many genera have received extensive study in the last two decades, however resolution of competing names in Cordycipitaceae has not yet been addressed. Here we present a molecular phylogenetic investigation of Cordycipitaceae that enables identification of competing names in this family, and provides the basis upon which these names can be maintained or suppressed. The taxonomy presented here seeks to harmonize competing names by principles of priority, recognition of monophyletic groups, and the practical usage of affected taxa. In total, we propose maintaining nine generic names, Akanthomyces, Ascopolyporus, Beauveria, Cordyceps, Engyodontium, Gibellula, Hyperdermium, Parengyodontium, and Simplicillium and the rejection of eight generic names, Evlachovaea, Granulomanus, Isaria, Lecanicillium, Microhilum, Phytocordyceps, Synsterigmatocystis, and Torrubiella. Two new generic names, Hevansia and Blackwellomyces, and a new species, Beauveria blattidicola, are described. New combinations are also proposed in the genera Akanthomyces, Beauveria, Blackwellomyces, and Hevansia.

Microbial associates of the southern mole cricket (Scapteriscus borellii) are highly pathogenic

We report the isolation and identification of seven bacterial strains and one fungal strain from dead and diseased Scapteriscus borellii mole crickets collected from a golf course in southern California. Using 16S and 18S rRNA gene sequence analysis we identified the microbes as Serratia marcescens (red), S. marcescens (white), S. marcescens (purple), Achromobacter xylosoxidans, Chryseobacterium sp., Ochrobactrum anthropi, Tsukamurella tryosinosolvens, and Beauveria bassiana. We performed a dose response curve for each of these cricket-associated microbial strains (except T. tryosinosolvens) and two other strains of S. marcescens (DB1140 and ATCC 13880). We found that all of these microbes except O. anthropi were highly pathogenic to D. melanogaster compared to the other strains of S. marcescens. Injecting the mole cricket associated strains of Serratia into flies killed all infected flies in ≤24h. For all other strains, the median time to death of injected flies varied in a dose-dependent manner. In vivo growth assessments of these microbes suggested that the host immune system was quickly overcome. We used disease tolerance curves to better understand the host-microbe interactions. Further studies are necessary to understand in mechanistic detail the virulence mechanisms of these mole cricket associated microbes and how this association may have influenced the evolution of mole cricket immunity.

Thioester-containing proteins regulate the Toll pathway and play a role in Drosophila defence against microbial pathogens and parasitoid wasps

BACKGROUND

Members of the thioester-containing protein (TEP) family contribute to host defence in both insects and mammals. However, their role in the immune response of Drosophila is elusive. In this study, we address the role of TEPs in Drosophila immunity by generating a mutant fly line, referred to as TEPq Δ , lacking the four immune-inducible TEPs, TEP1, 2, 3 and 4.

RESULTS

Survival analyses with TEPq Δ flies reveal the importance of these proteins in defence against entomopathogenic fungi, Gram-positive bacteria and parasitoid wasps. Our results confirm that TEPs are required for efficient phagocytosis of bacteria, notably for the two Gram-positive species tested, Staphylococcus aureus and Enterococcus faecalis. Furthermore, we show that TEPq Δ flies have reduced Toll pathway activation upon microbial infection, resulting in lower expression of antimicrobial peptide genes. Epistatic analyses suggest that TEPs function upstream or independently of the serine protease ModSP at an initial stage of Toll pathway activation.

CONCLUSIONS

Collectively, our study brings new insights into the role of TEPs in insect immunity. It reveals that TEPs participate in both humoral and cellular arms of immune response in Drosophila. In particular, it shows the importance of TEPs in defence against Gram-positive bacteria and entomopathogenic fungi, notably by promoting Toll pathway activation.

Beauveria bassiana and Metarhizium anisopliae endophytically colonize cassava roots following soil drench inoculation

We investigated the fungal entomopathogens Beauveria bassiana and Metarhizium anisopliae to determine if endophytic colonization could be achieved in cassava. An inoculation method based on drenching the soil around cassava stem cuttings using conidial suspensions resulted in endophytic colonization of cassava roots by both entomopathogens, though neither was found in the leaves or stems of the treated cassava plants. Both fungal entomopathogens were detected more often in the proximal end of the root than in the distal end. Colonization levels of B. bassiana were higher when plants were sampled at 7-9 days post-inoculation (84%) compared to 47-49 days post-inoculation (40%). In contrast, the colonization levels of M. anisopliae remained constant from 7-9 days post-inoculation (80%) to 47-49 days post-inoculation (80%), which suggests M. anisopliae is better able to persist in the soil, or as an endophyte in cassava roots over time. Differences in colonization success and plant growth were found among the fungal entomopathogen treatments.

Disease Dynamics in Ants: A Critical Review of the Ecological Relevance of Using Generalist Fungi to Study Infections in Insect Societies

It is assumed that social life can lead to the rapid spread of infectious diseases and outbreaks. In ants, disease outbreaks are rare and the expression of collective behaviors is invoked to explain the absence of epidemics in natural populations. Here, we address the ecological approach employed by many studies that have notably focused (89% of the studies) on two genera of generalist fungal parasites (Beauveria and Metarhizium). We ask whether these are the most representative models to study the evolutionary ecology of ant-fungal parasite interactions. To assess this, we critically examine the literature on ants and their interactions with fungal parasites from the past 114years (1900-2014). We discuss how current evolutionary ecology approaches emerged from studies focused on the biological control of pest ants. We also analyzed the ecological relevance of the laboratory protocols used in evolutionary ecology studies employing generalist parasites, as well as the rare natural occurrence of these parasites on ants. After a detailed consideration of all the publications, we suggest that using generalist pathogens such as Beauveria and Metarhizium is not an optimal approach if the goal is to study the evolutionary ecology of disease in ants. We conclude by advocating for approaches that incorporate greater realism.

Advances in Genomics of Entomopathogenic Fungi

Fungi are the commonest pathogens of insects and crucial regulators of insect populations. The rapid advance of genome technologies has revolutionized our understanding of entomopathogenic fungi with multiple Metarhizium spp. sequenced, as well as Beauveria bassiana, Cordyceps militaris, and Ophiocordyceps sinensis among others. Phylogenomic analysis suggests that the ancestors of many of these fungi were plant endophytes or pathogens, with entomopathogenicity being an acquired characteristic. These fungi now occupy a wide range of habitats and hosts, and their genomes have provided a wealth of information on the evolution of virulence-related characteristics, as well as the protein families and genomic structure associated with ecological and econutritional heterogeneity, genome evolution, and host range diversification. In particular, their evolutionary transition from plant pathogens or endophytes to insect pathogens provides a novel perspective on how new functional mechanisms important for host switching and virulence are acquired. Importantly, genomic resources have helped make entomopathogenic fungi ideal model systems for answering basic questions in parasitology, entomology, and speciation. At the same time, identifying the selective forces that act upon entomopathogen fitness traits could underpin both the development of new mycoinsecticides and further our understanding of the natural roles of these fungi in nature. These roles frequently include mutualistic relationships with plants. Genomics has also facilitated the rapid identification of genes encoding biologically useful molecules, with implications for the development of pharmaceuticals and the use of these fungi as bioreactors.

Insect Pathogenic Fungi as Endophytes

In this chapter, we explore some of the evolutionary, ecological, molecular genetics, and applied aspects of a subset of insect pathogenic fungi that also have a lifestyle as endophytes and we term endophytic insect pathogenic fungi (EIPF). We focus particularly on Metarhizium spp. and Beauveria bassiana as EIPF. The discussion of the evolution of EIPF challenges a view that these fungi were first and foremost insect pathogens that eventually evolved to colonize plants. Phylogenetic evidence shows that the lineages of EIPF are most closely related to grass endophytes that diverged c. 100MYA. We discuss the relationship between genes involved in "insect pathogenesis" and those involved in "endophytism" and provide examples of genes with potential importance in lifestyle transitions toward insect pathogenicity. That is, some genes for insect pathogenesis may have been coopted from genes involved in endophytic colonization. Other genes may be multifunctional and serve in both lifestyle capacities. The interactions of EIPF with their host plants are discussed in some detail. The genetic basis for rhizospheric competence, plant communication, and nutrient exchange is examined and we highlight, with examples, the benefits of EIPF to plants, and the potential reservoir of secondary metabolites hidden within these beneficial symbioses.

New insights into the amphibious life of Biomphalaria glabrata and susceptibility of its egg masses to fungal infection

The air-breathing snail Biomphalaria glabrata proliferates in stagnant freshwater, and nothing is known about the survival of eggs in intermittently (rather than perpetually) wet habitats. In the present study their egg masses matured, and juveniles subsequently eclosed and were mobile in a stable water film of transitory habitats simulated by two different simple test devices described here. The viability of eggs maintained in an unstable film however, was diminished. The maturation of egg masses in a water film or in water was significantly prevented by the entomopathogenic fungi Beauveria bassiana and Metarhizium anisopliae. The efficiency depended on the fungal propagule and test environment. Hyphal bodies were more effective against egg masses than conidia. This appears to be a first report of activity of either entomopathogen against a mollusc. Both devices offer accurate and reproducible conditions to test both biological questions and the effects of substances or pathogens against B. glabrata egg masses in water films.

Pathogenicity of conidia-based preparations of entomopathogenic fungi against the greenhouse pest aphids Myzus persicae, Aphis gossypii, and Aulacorthum solani (Hemiptera: Aphididae)

Seeking new isolates of entomopathogenic fungi with greater virulence against greenhouse aphid pests than those currently registered in North America for control of these insects, single-dose screening assays of 44 selected fungal isolates and 4 commercially available strains were conducted against first-instar nymphs of Myzus persicae and Aphis gossypii. The assays identified a number of Beauveria and Metarhizium isolates with virulence equal to or greater than that of the commercial strains against the nymphal aphids, but none exhibited exceptionally high virulence. Virulence of Isaria isolates was unexpectedly low (<31% mortality at doses>1000conidia/mm(2)). In dose-response assays, Beauveria ARSEF 5493 proved most virulent against M. persicae and A. gossypii; however, LC50s of this isolate did not differ significantly from those of B. bassiana commercial strain JW-1. Dose-response assays were also conducted with Aulacorthum solani, the first reported evaluations of Beauveria and Metarhizium against this pest. The novel isolate Metarhizium 5471 showed virulence⩾that of Beauveria 5493 in terms of LC25 and LC50, but 5493 produced a steeper dose response (slope). Additional tests showed that adult aphids are more susceptible than nymphs to fungal infection but confirmed that infection has a limited pre-mortem effect on aphid reproduction. Effects of assay techniques and the potential of fungal pathogens as aphid-control agents are discussed.