A Review of Commercial Metarhizium- and Beauveria-Based Biopesticides for the Biological Control of Ticks in the USA

Modeling platform to assess the effectiveness of single and integrated Ixodes scapularis tick control methods

BACKGROUND

Lyme disease continues to expand in Canada and the USA and no single intervention is likely to curb the epidemic.

METHODS

We propose a platform to quantitatively assess the effectiveness of a subset of Ixodes scapularis tick management approaches. The platform allows us to assess the impact of different control treatments, conducted either individually (single interventions) or in combination (combined efforts), with varying timings and durations. Interventions include three low environmental toxicity measures in differing combinations, namely reductions in white-tailed deer (Odocoileus virginianus) populations, broadcast area-application of the entomopathogenic fungus Metarhizium anisopliae, and fipronil-based rodent-targeted bait boxes. To assess the impact of these control efforts, we calibrated a process-based mathematical model to data collected from residential properties in the town of Redding, southwestern Connecticut, where an integrated tick management program to reduce I.xodes scapularis nymphs was conducted from 2013 through 2016. We estimated parameters mechanistically for each of the three treatments, simulated multiple combinations and timings of interventions, and computed the resulting percent reduction of the nymphal peak and of the area under the phenology curve.

RESULTS

Simulation outputs suggest that the three-treatment combination and the bait boxes-deer reduction combination had the overall highest impacts on suppressing I. scapularis nymphs. All (single or combined) interventions were more efficacious when implemented for a higher number of years. When implemented for at least 4 years, most interventions (except the single application of the entomopathogenic fungus) were predicted to strongly reduce the nymphal peak compared with the no intervention scenario. Finally, we determined the optimal period to apply the entomopathogenic fungus in residential yards, depending on the number of applications.

CONCLUSIONS

Computer simulation is a powerful tool to identify the optimal deployment of individual and combined tick management approaches, which can synergistically contribute to short-to-long-term, costeffective, and sustainable control of tick-borne diseases in integrated tick management (ITM) interventions.

Isolation and characterization of a native strain of the entomopathogenic fungus Beauveria bassiana for the control of the palm weevil Dynamis borassi (Coleoptera: Curculionidae) in the neotropics

This study aimed to isolate and characterize a native strain of Beauveria bassiana, coded as Bv065, showcasing its potential as a biological control agent targeting the palm weevil Dynamis borassi. Originating from a naturally infected D. borassi specimen collected in southwestern Colombia, the fungus underwent molecular identification and was identified as B. bassiana, exhibiting high sequence similarity with known reference strains. The physiological characterization revealed that Bv065 thrived within a temperature range of 25 to 30 °C and a pH range of 6 to 9. Moreover, the key carbon sources that allow optimal growth of the strain were identified through metabolic profiling, including sucrose, D-mannose, and γ-amino-butyric acid. These findings offer strategic insights for scalability and formulation methodologies. Additionally, enzymatic analyses unveiled robust protease activity within Bv065, crucial for catalysing insect cuticle degradation and facilitating host penetration, thus accentuating its entomopathogenic potential. Subsequent evaluations exposed Bv065's pathogenicity against D. borassi, causing significant mortality within nine days of exposure, albeit exhibiting limited effectiveness against Rhynchophorus palmarum. This study underscores the importance of understanding optimal growth conditions and metabolic preferences of B. bassiana strains for developing effective biopesticides. The findings suggest Bv065 as a promising candidate for integrated pest management strategies in neotropical regions, particularly for controlling palm weevil infestations in coconut and peach palm cultivation. Future research avenues include refining mass production methodologies, formulating novel delivery systems, and conducting comprehensive field efficacy trials to unlock the full potential of Bv065 in fostering sustainable pest management practices. Overall, this study contributes to the growing body of knowledge on entomopathogenic fungi and their pivotal role in biological control, offering nuanced perspectives on eco-friendly alternatives to conventional insecticidal interventions.

Assessment of Fungal Lytic Enzymatic Extracts Produced Under Submerged Fermentation as Enhancers of Entomopathogens' Biological Activity

The application of enzymes in agricultural fields has been little explored. One potential application of fungal lytic enzymes (chitinases, lipases, and proteases) is as an additive to current biopesticides to increase their efficacy and reduce the time of mortality. For this, a screening of lytic overproducer fungi under submerged fermentation with a chemical-defined medium was performed. Then, the enzymatic crude extract (ECE) was concentrated and partially characterized. This characterization consisted of measuring the enzymatic activity (lipase, protease and, chitinase) and determining the enzyme stability after storage at temperatures of - 80, - 20 and, 4 °C. And lastly, the application of these concentrated enzymatic crude extracts (C-ECE) as an enhancer of spores-based fungal biopesticide was proven. Beauveria were not as good producers of lytic enzymes as the strains from Trichoderma and Metarhizium. The isolate M. robertsii Mt015 was selected for the co-production of chitinases and proteases; and the isolate T. harzianum Th180 for co-production of chitinases, lipases, and proteases. The C-ECE of Mt015 had a protease activity of 18.6 ± 1.1 U ml-1, chitinase activity of 0.28 ± 0.01 U ml-1, and no lipase activity. Meanwhile, the C-ECE of Th180 reached a chitinase activity of 0.75 U ml-1, lipase activity of 0.32 U ml-1, and protease activity of 0.24 U ml-1. Finally, an enhancing effect of the enzymatic extracts of M. robertsii (66.7%) and T. harzianum (43.5%) on the efficacy of B. bassiana Bv064 against Diatraea saccharalis larvae was observed. This work demonstrates the non-species-specific enhancing effect of enzymatic extracts on the insecticidal activity of conidial-based biopesticides, which constitutes a contribution to the improvement of biological control agents' performance.

New paradigms in the prevention of canine vector-borne diseases

The prevention of canine vector-borne diseases (CVBDs) is pivotal for the health and welfare of dogs as well as for reducing their zoonotic risk to humans. Scientific knowledge gained in recent years contributed to the development of new strategies for the control of these diseases in different social and cultural contexts. Here, we discuss recent advances in the prevention of vector-borne pathogens (VBPs) affecting dogs with a focus on those of zoonotic relevance.

Entomopathogenic Fungi in Forest Habitats of Ixodes ricinus

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

Utilization of CRISPR-Cas genome editing technology in filamentous fungi: function and advancement potentiality

Filamentous fungi play a crucial role in environmental pollution control, protein secretion, and the production of active secondary metabolites. The evolution of gene editing technology has significantly improved the study of filamentous fungi, which in the past was laborious and time-consuming. But recently, CRISPR-Cas systems, which utilize small guide RNA (sgRNA) to mediate clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated proteins (Cas), have demonstrated considerable promise in research and application for filamentous fungi. The principle, function, and classification of CRISPR-Cas, along with its application strategies and research progress in filamentous fungi, will all be covered in the review. Additionally, we will go over general matters to take into account when editing a genome with the CRISPR-Cas system, including the creation of vectors, different transformation methodologies, multiple editing approaches, CRISPR-mediated transcriptional activation (CRISPRa) or interference (CRISPRi), base editors (BEs), and Prime editors (PEs).

Variation in Bombyx mori immune response against fungal pathogen Beauveria bassiana with variability in cell wall β-1,3-glucan

Entomopathogenic fungi are protected by a cell wall with dynamic structure for adapting to various environmental conditions. β-1,3-Glucan recognition proteins activate the innate immune system of insects by recognizing surface molecules of fungi. However, the associations between pathogenicity and the different components of entomopathogenic fungal cell walls remain unclear. Three Beauveria bassiana strains were selected that have significantly differing virulence against Bombyx mori. The molecular mechanisms underlying the immune response in B. mori were investigated using RNA sequencing, which revealed differences in the immune response to different B. bassiana strains at 12 h post-infection. Immunofluorescence assays revealed that β-1,3-glucan content had an opposite trend to that of fungal virulence. β-1,3-Glucan injection upregulated BmβGRP4 expression and significantly reduced the virulence of the high-virulence strain but not that of the medium-virulence or low-virulence strains. BmβGRP4 silencing in B. mori with RNA interference resulted in the opposite virulence pattern, indicating that the virulence of B. bassiana was affected by the cell walls' content of β-1,3-glucan, which could be recognized by BmβGRP4. Furthermore, interference with the gene CnA (calcineurin catalytic A subunit) involved in β-1,3-glucan synthesis eliminated differences in virulence between B. bassiana strains. These results indicate that strains of a single species of pathogenic fungi that have differing cell wall components are recognized differently by the innate immune system of B. mori.

Nano-Agrochemicals as Substitutes for Pesticides: Prospects and Risks

This review delves into the mesmerizing technology of nano-agrochemicals, specifically pesticides and herbicides, and their potential to aid in the achievement of UN SDG 17, which aims to reduce hunger and poverty globally. The global market for conventional pesticides and herbicides is expected to reach USD 82.9 billion by 2027, growing 2.7% annually, with North America, Europe, and the Asia-Pacific region being the biggest markets. However, the extensive use of chemical pesticides has proven adverse effects on human health as well as the ecosystem. Therefore, the efficacy, mechanisms, and environmental impacts of conventional pesticides require sustainable alternatives for effective pest management. Undoubtedly, nano-agrochemicals have the potential to completely transform agriculture by increasing crop yields with reduced environmental contamination. The present review discusses the effectiveness and environmental impact of nanopesticides as promising strategies for sustainable agriculture. It provides a concise overview of green nano-agrochemical synthesis and agricultural applications, and the efficacy of nano-agrochemicals against pests including insects and weeds. Nano-agrochemical pesticides are investigated due to their unique size and exceptional performance advantages over conventional ones. Here, we have focused on the environmental risks and current state of nano-agrochemicals, emphasizing the need for further investigations. The review also draws the attention of agriculturists and stakeholders to the current trends of nanomaterial use in agriculture especially for reducing plant diseases and pests. A discussion of the pros and cons of nano-agrochemicals is paramount for their application in sustainable agriculture.

The complete mitogenome of the entomopathogenic fungus Metarhizium pinghaense 15R

In this study, the complete mitogenome of the entomopathogenic fungus Metarhizium pinghaense 15 R, which is highly virulent to aphids and was isolated from Korean soil, was assembled and annotated for three ATP synthase subunits (atp6, atp8, and atp9), three cytochrome oxidase subunits (cox1, cox2, and cox3), apocytochrome b (cob), seven subunits of NADH dehydrogenase (nad1, nad2, nad3, nad4, nad4L, nad5, and nad6), two ribosomal RNAs (rnl and rns), and 19 tRNA genes. Five genes were carrying a total of eight introns, and they may encode ribosomal protein S3, LAGLIDADG and GIY-YIG endonucleases. Phylogenetic analysis based on the mitochondrial nucleotide sequence confirmed that the M. pinghaense 15 R is a member of the Clavicipitaceae, and is closely related to the species M. anisopliae, M. robertsii, and M. brunneum. The mtDNA base sequence of the M. pinghaense 15 R strain reported in this study is thought to be useful for biological resource genetic data.

Species Discrimination within the Metarhizium PARB Clade: Ribosomal Intergenic Spacer (rIGS)-Based Diagnostic PCR and Single Marker Taxonomy

(1) Background: The entomopathogenic fungus Metarhizium anisopliae sensu lato forms a species complex, comprising a tight cluster made up of four species, namely M. anisopliae sensu stricto, M. pinghaense, M. robertsii and M. brunneum. Unambiguous species delineation within this "PARB clade" that enables both the taxonomic assignment of new isolates and the identification of potentially new species is highly solicited. (2) Methods: Species-discriminating primer pairs targeting the ribosomal intergenic spacer (rIGS) sequence were designed and a diagnostic PCR protocol established. A partial rIGS sequence, referred to as rIGS-ID800, was introduced as a molecular taxonomic marker for PARB species delineation. (3) Results: PARB species from a validation strain set not implied in primer design were clearly discriminated using the diagnostic PCR protocol developed. Using rIGS-ID800 as a single sequence taxonomic marker gave rise to a higher resolution and statistically better supported delineation of PARB clade species. (4) Conclusions: Reliable species discrimination within the Metarhizium PARB clade is possible through both sequencing-independent diagnostic PCR and sequencing-dependent single marker comparison, both based on the rIGS marker.

Community-based integrated tick management programs: cost and feasibility scenarios

Numerous studies have assessed the efficacy of environmentally based control methods to suppress populations of the blacklegged tick (Ixodes scapularis Say), but few of these estimated the cost of control. We estimated costs for a range of tick control methods (including habitat management, deer exclusion or population reduction, broadcast of acaricides, and use of host-targeted acaricides) implemented singly or in combination and applied to a model community comprising 320 residential properties and parklands. Using the high end for cost ranges, tick control based on a single method was estimated to have mean annual costs per household in the model community ranging from $132 for treating only forest ecotone with a broadcast synthetic acaricide to kill host-seeking ticks (or $404 for treating all residential forested habitat) to >$2,000 for deployment of bait boxes (SELECT TCS) across all residential tick habitat to treat rodents topically with acaricide to kill infesting ticks. Combining different sets of multiple methods in an integrated tick management program placed the annual cost between $508 and 3,192 annually per household in the model community, underscoring the disconnect between what people in Lyme disease endemic areas say they are willing to pay for tick control (not more than $100-150 annually) and the actual costs for tick control. Additional barriers to implementing community-based tick management programs within residential communities are discussed.

Entomopathogenic fungus Beauveria bassiana-based bioinsecticide suppresses severity of powdery mildews of vegetables by inducing the plant defense responses

The entomopathogenic fungus Beauveria bassiana is used commercially as a microbial insecticides against a wide range of agricultural insect pests. Some strains of B. bassiana protect the plants from pathogens, but the underlying mechanisms are largely unknown. Here, we found that prophylactic sprays of commercial bioinsecticide Botanigard on cucumber, tomato, and strawberry plants suppressed the severity of economically damaging powdery mildews. On leaf surfaces, hyphal elongation and spore germination of cucumber powdery mildew, Podosphaera xanthii, were inhibited, but B. bassiana strain GHA, the active ingredient isolated from Botanigard, only inhibited hyphal elongation but had no effect on spore germination of P. xanthii. In addition, strain GHA suppressed powdery mildew symptoms locally, not systemically. Treatment with Botanigard and strain GHA induced a hypersensitive response (HR)-like cell death in epidermal cells of the cucumber leaves in a concentration-dependent manner and inhibited penetration by P. xanthii. Transcriptome analysis and mass spectrometry revealed that GHA induced expression of salicylic acid (SA)-related genes, and treatment with Botanigard and GHA increased the SA level in the cucumber leaves. In NahG-transgenic tomato plants, which do not accumulate SA, the biocontrol effect of tomato powdery mildew by GHA was significantly reduced. These results suggested that B. bassiana GHA induces SA accumulation, leading to the induction of HR-like cell death against powdery mildew and subsequent suppression of fungal penetration. Thus, Botanigard has the potential to control both insect pests and plant diseases.

Metarhizium anisopliae E6 secretome reveals molecular players in host specificity and toxicity linked to cattle tick infection

Although Metarhizium anisopliae is one of the most studied fungal biocontrol agents, its infection mechanism is far from being completely understood. Using multidimensional protein identification technology (MudPIT), we evaluated the differential secretome of M. anisopliae E6 induced by the host Rhipicephalus microplus cuticle. The proteomic result showed changes in the expression of 194 proteins after exposure to host cuticle, such as proteins involved in adhesion, penetration, stress and fungal defense. Further, we performed a comparative genomic distribution of differentially expressed proteins of the M. anisopliae secretome against another arthropod pathogen, using the Beauveria bassiana ARSEF2860 protein repertory. Among 47 analyzed protein families, thirty were overexpressed in the M. anisopliae E6 predicted genome compared to B. bassiana. An in vivo toxicity assay using a Galleria mellonella model confirmed that the M. anisopliae E6 secretome was more toxic in cattle tick infections compared to other secretomes, including B. bassiana with cattle ticks and M. anisopliae E6 with the insect Dysdereus peruvianus, which our proteomic results had also suggested. These results help explain molecular aspects associated with host infection specificity due to genetic differences and gene expression control at the protein level in arthropod-pathogenic fungi.

Entomopathogenicity of Ascomycete Fungus Cordyceps militaris on the Cotton Bollworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae)

This study investigated the exposure of the cotton bollworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) to a novel pathogenic fungal agent historically associated with human medicinal value, a commercial strain of Cordyceps militaris ((L.) Fr.) Vuill. (Hypocreales). A series of comparative studies were conducted to evaluate the efficacy of two different exposure methods using four concentrations (n × 10⁹, n × 10⁸, n × 10⁷, n × 10⁶) of C. militaris, where n × 10⁹ provided a concentration of approximately 420 ± 37 spores per mm² with 398 ± 28 viable spores. Survival of cotton bollworms of all stages was not affected by C. militaris at any concentration 1 d post-exposure. The greatest reduction in survival and highest sporulation rates were observed primarily on or after 7 d post-exposure for early instars (first and second). Significant declines in the survival of early instars were observed for all concentrations at 7 d, and 95% mortality by 10 d, with the exception of the fifth instars that experienced a less severe reduction in survival (35%) when exposed to any concentrations used in the study. Survival of late instars (third to fifth) ranged from 44% to 68% on day 10, while adult survival was near 99% across the duration of the experiment. The relatively narrow range observed for both the lethal concentration and sporulation of second, third, and fifth instar cotton bollworms exposed to the C. militaris strain may demonstrate potential field application for control of larval populations of cotton bollworms.

Field efficacy of Metarhizium anisopliae oil formulations against Rhipicephalus microplus ticks using a cattle spray race

Rhipicephalus microplus tick is the main ectoparasite of cattle in Brazil. The exhaustive use of chemical acaricides to control this tick has favored the selection of resistant tick populations. Entomopathogenic fungi, as Metarhizium anisopliae, has been described as a potential biocontroller of ticks. Therefore, the aim of this study was to evaluate the in vivo efficacy of two oil based formulations of M. anisopliae for the control of the cattle tick R. microplus under field conditions using a cattle spray race as a method of treatment. Initially, in vitro assays were carried out with an aqueous suspension of M. anisopliae, using mineral oil and/or silicon oil. A potential synergism between oils and fungus conidia for tick control was demonstrated. Additionally, the usefulness of silicon oil in order to reduce mineral oil concentration, while improving formulation efficacy was illustrated. Based on the in vitro results, two formulations were selected for use in the field trial: MaO1 (10⁷ conidia/mL plus 5% mineral oil) and MaO2 (10⁷ conidia/mL plus 2.5% mineral oil and 0.01% silicon oil). The adjuvants concentrations (mineral and silicon oils) were chosen since preliminary data indicate that higher concentrations caused significant mortality in adult ticks. For this, 30 naturally infested heifers were divided into three groups based on previous tick counts. The control group did not receive treatment. The selected formulations were applied on animals using a cattle spray race. Subsequently, tick load was evaluated weekly by counting. The MaO1 treatment significantly reduced the tick count only on day +21, reaching approximately 55% efficacy. On the other hand, MaO2 showed significantly lower tick counts on days +7, +14, and +21 after treatment, with weekly efficacy achieving 66%. The results showed a substantial reduction of tick infestation, up to day +28, using a novel formulation of M. anisopliae based in the mixture of two oils. Moreover, we have shown, for the first time, the feasibility of employing formulations of M. anisopliae for large-scale treatment methods, such as a cattle spray race, which in turn, may increase the use and adhesion to biological control tools among farmers.

Diversity of entomopathogenic fungi from soils of eucalyptus and soybean crops and natural forest areas

Soils present high fungal diversity, including entomopathogenic species. These fungi are used in pest control, providing easy production, multiplication, application, and dispersion in the field. The objective of the present study was to evaluate entomopathogenic fungal diversity in soils from eucalyptus and soybean crops and natural forest areas. These fungi were isolated using the "Bait Method" with Tenebrio molitor (Linnaeus, 1758) (Coleoptera: Tenebrionidae) larvae from 10 soil samples per area, collected at 10 cm deep in a zig-zag pattern. The isolated entomopathogenic fungi were cultivated in Petri dishes using PDA medium and their mycelia separated after seven days of incubation in a BOD-type chamber. Species of Aspergillus, Beauveria, Cordyceps, Fusarium, Metarhizium, Penicillium and Purpureocillium were identified. The "Bait Method" with T. molitor larvae is efficient to isolate entomopathogenic fungi with higher diversity from soils of the natural forest than the cultivated area.

Pathogenicity of Beauveria bassiana PfBb and Immune Responses of a Non-Target Host, Spodoptera frugiperda (Lepidoptera: Noctuidae)

Exploring the pathogenicity of a new fungus strain to non-target host pests can provide essential information on a large scale for potential application in pest control. In this study, we tested the pathogenicity of Beauveria bassiana PfBb on the important agricultural pest Spodoptera frugiperda (Lepidoptera: Noctuidae) by determining the relative activities of protective enzymes and detoxifying enzymes in different larval instars. Our results show that the B. bassiana PfBb strain could infect all six larval instars of S. frugiperda, and its virulence to S. frugiperda larvae gradually increased with an increase in spore concentration. Seven days after inoculation, the LC₅₀ of B. bassiana PfBb was 7.7 × 10⁵, 5.5 × 10⁶, 2.2 × 10⁷, 3.1 × 10⁸, 9.6 × 10⁸, and 2.5 × 10¹¹ spores/mL for first to sixth instars of S. frugiperda, respectively, and the LC₅₀ and LC₉₀ of B. bassiana PfBb for each S. frugiperda instar decreased with infection time, indicating a significant dose effect. Furthermore, the virulence of B. bassiana PfBb to S. frugiperda larvae gradually decreased with an increase in larval instar. The activities of protective enzymes (i.e., catalase, peroxidase, and superoxide dismutase) and detoxifying enzymes (i.e., glutathione S-transferases, carboxylesterase, and cytochrome P450) in S. frugiperda larvae of the first three instars infected with B. bassiana PfBb changed significantly with infection time, but such variations were not obvious in the fifth and sixth instars. Additionally, after being infected with B. bassiana PfBb, the activities of protective enzymes and detoxification enzymes in S. frugiperda larvae usually lasted from 12 to 48 h, which was significantly longer than the control. These results indicate that the pathogenicity of B. bassiana PfBb on the non-target host S. frugiperda was significant but depended on the instar stage. Therefore, the findings of this study suggest that B. bassiana PfBb can be used as a bio-insecticide to control young larvae of S. frugiperda in an integrated pest management program.