Metarhizium rileyi biopesticide to control Spodoptera frugiperda: Stability and insecticidal activity under glasshouse conditions

Construction of an Efficient Agrobacterium tumefaciens-Based Transformation System in the Entomopathogenic fungus Metahizium rileyi

Metarhizium rileyi is a filamentous entomopathogenic fungus that is highly pathogenic to lepidopteran insects. In our study, we constructed an Agrobacterium tumefaciens-mediated transgene system using the hygromycin resistance gene (Hyg R) as a selection marker in M. rileyi through homologous recombination. Binary knockout vectors for two genes (NOR_03501, longevity assurance gene, and NOR_03153, ATP-binding domain protein domain gene) in the M. rileyi strain SZCY201010 were successfully developed. We compared the genetic transformation efficiency using five kinds of asexual spores. The initial genetic transformation rates using a competent blastospore for NOR_03501 and NOR_03153 were 54.35 and 47.19%, respectively. Subsequently, both genes were successfully knocked out, and the transformed fungi were verified by PCR, RT-qPCR, and green fluorescent protein labeling. The biological phenotypes of the two genes were analyzed. The NOR_03501 gene plays a crucial role in carbon source utilization, stress resistance, and cuticle infection of fungal mycelium growth, while the NOR_03153 gene is significant for conidial production, stress resistance, and body wall infection. This study provides a promising tool for gene manipulation in M. rileyi, enhancing research in functional genomics and the exploration of fungal gene resources.

Oleic Acid and Linoleic Acid Enhances the Biocontrol Potential of Metarhizium rileyi

Metarhizium rileyi is a wide spread insect fungi with a good biocontrol potentiality to various pests, particularly noctuid insects. However, it is characterized by its slow growth, its sensitivity to abiotic stress, and the slow speed of kill to pests, which hinder its use compared with other entomopathogenic fungi. In this study, the responses of M. rileyi to eight types of lipids were observed; among the lipids, oleic acid and linoleic acid significantly promoted the growth and development of M. rileyi and enhanced its stress tolerances and virulence. An additional mechanistic study demonstrated that exogenous oleic acid and linoleic acid significantly improved the conidial germination, appressorium formation, cuticle degradation, and cuticle infection, which appear to be largely dependent on the up-regulation of gene expression in growth, development, protective, and cuticle-degrading enzymes. In conclusion, exogenous oleic acid and linoleic acid enhanced the stress tolerances and virulence of M. rileyi via protecting conidial germination and promoting cuticle infection. These results provide new insights for the biopesticide development of M. rileyi.

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.

A new endophytic Penicillium oxalicum with aphicidal activity and its infection mechanism

BACKGROUND

Aphid infestation adversely affects the yield and quality of crops. Rapid reproduction and insecticidal resistance have made controlling aphids in the field challenging. Therefore, the present study investigated the insecticidal property of Penicillium oxalicum (QLhf-1) and its mechanism of action against aphids, Hyalopterus arundimis Fabricius.

RESULTS

Bioassay revealed that the control efficacy of the spores against aphids (86.30% and 89.05% on the third day and fifth day after infection, respectively) were higher than other components, such as the mycelium. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that QLhf-1 invaded the aphid cuticle through spores and used the aphid tissues as a nutrient source for growth and reproduction, causing stiffness and atrophy and a final death. Three extracellular enzymes, lipase, protease, and chitinase had a synergistic effect with spores, and they acted together to complete the infection process by degrading the aphid body wall and accelerating the infection process.

CONCLUSION

The newly discovered endophytic penicillin strain P. oxalicum 'QLhf-1' can effectively kill aphids. The results provided strong evidence for the biological control of aphids, and lay a foundation for the development and utilization of QLhf-1. © 2024 Society of Chemical Industry.

Metarhizium rileyi with broad-spectrum insecticidal ability confers resistance against phytopathogens and insect pests as a phytoendophyte

BACKGROUND

Entomophagous fungi (EPF) not only directly kill insect pests, but also colonize plants and improve their resistance against pests. However, most previous research has focused on Beauveria bassiana and Metarhizium anisopliae, and there are few reports on whether other EPF can enhance resistance against pests via endogenous colonization. Herein, an EPF strain was isolated from diseased larvae of Spodoptera litura in a soybean field, and subjected to genome-wide sequencing at the chromosomal level. The pathogenicity of the isolate toward various pest insects was evaluated, and the ability to colonize plants and induce resistance against phytopathogens and insect pests was tested.

RESULTS

The purified isolate was identified as M. rileyi and designated MrS1Gz1-1. Biological assays revealed its strong pathogenicity toward five insect pests belonging to Lepidoptera and Hemiptera. Furthermore, the strain inhibited the growth of soil-borne plant disease caused by Sclerotinia sclerotiorum in vitro. It colonized plants as an endophyte via soil application, thereby inducing plant resistance-related genes against phytopathogen infection, and it disrupted the feeding selectivity of S. litura larvae.

CONCLUSION

M. rileyi MrS1Gz1-1 has potential as a broad-spectrum microbial control agent that can induce resistance against phytopathogens and insect pests feeding as an endotype. The complete genome provides a valuable resource for exploring host interactions. © 2024 Society of Chemical Industry.

Physiological response of Metarhizium rileyi with linoleic acid supplementation

Metarhizium rileyi has a broad biocontrol spectrum but is highly sensitive to abiotic factors. A Colombian isolate M. rileyi Nm017 has shown notorious potential against Helicoverpa zea. However, it has a loss of up to 22 % of its conidial germination after drying, which limits its potential as a biocontrol agent and further commercialization. Conidial desiccation resistance can be enhanced by nutritional supplements, which promotes field adaptability and facilitates technological development as a biopesticide. In this study, the effect of culture medium supplemented with linoleic acid on desiccation tolerance in Nm017 conidia was evaluated. Results showed that using a 2 % linoleic acid-supplemented medium increased the relative germination after drying by 41 % compared to the control treatment, without affecting insecticidal activity on H. zea. Also, the fungus increased the synthesis of trehalose, glucose, and erythritol during drying, independently of linoleic acid use. Ultrastructural analyses of the cell wall-membrane showed a loss of thickness by 22 % and 25 %, in samples obtained from 2 % linoleic acid supplementation and the control, respectively. Regarding its morphological characteristics, conidia inner area from both treatments did not change after drying. However, conidia from the control had a 24 % decrease in length/width ratio, whereas there was no alteration in conidia from acid linoleic. The average value of dry conidia elasticity coefficient from linoleic acid treatment was 200 % above the control. Medium supplementation with linoleic acid is a promising fermentation strategy for obtaining more tolerant conidia without affecting production and biocontrol parameters, compatible solutes synthesis, or modifying its cell configuration.

Performance of Metarhizium rileyi Nm017: nutritional supplementation to improve production and quality conidia

This study aimed to analyze the effect of nutritional supplements on improving conidia production of Metarhizium rileyi Nm017 at laboratory scale (yields of conidia/substrate and biomass/substrate, and substrate consumption). Also, the influence on quality parameters were evaluated (germination at 36 and 48 h, enzymatic activity, and insecticidal activity on Helicoverpa zea). Six treatments (T1-T6) were assessed and all of them reached maximum conidia concentration after 7 days fermentation, a feasible production timetable. Yields from treatment T6 (yeast extract + V8 juice) were 1.5-threefold higher than the other treatments. Conidia from T6 reached germinations of 56% and 12% at 36 and 48 h, respectively, higher than T1 (without supplements), which had the lowest values found. M. rileyi conidia obtained from treatment T6 had the highest enzymatic activity (0.45 U chitinase g-1, 0.28 U lipase g-1, and 1.29 U protease g-1). However, treatments with the highest conidia yields and enzymatic activity were not positively correlated to the efficacy against H. zea. When M. rileyi was produced on T5 (yeast hydrolysate + V8 juice), conidia were 35% more virulent than treatment T6. The findings evidenced the noticeable impact of nutritional substrate amended for conidia production and quality. This work showed the relevance of insecticidal activity assessment as a selection criterion in the mass production development of a biocontrol agent.

First record of Aspergillus nomiae as a broad-spectrum entomopathogenic fungus that provides resistance against phytopathogens and insect pests by colonization of plants

Introduction

Aspergillus nomiae is known as a pathogenic fungus that infects humans and plants but has never been reported as an entomophagous fungus (EPF) that can provide other functions as an endotype.

Methods

A strain of EPF was isolated and identified from diseased larvae of Spodoptera litura in a soybean field and designated AnS1Gzl-1. Pathogenicity of the strain toward various insect pests was evaluated, especially the ability to colonize plants and induce resistance against phytopathogens and insect pests.

Results

The isolated EPF strain AnS1Gzl-1 was identified as A. nomiae; it showed strong pathogenicity toward five insect pests belonging to Lepidoptera and Hemiptera. Furthermore, the strain inhibited the growth of Sclerotinia sclerotiorum in vitro, a causal agent of soil-borne plant disease. It colonized plants as an endophyte via root irrigation with a high colonization rate of 90%, thereby inducing plant resistance against phytopathogen infection, and disrupting the feeding selectivity of S. litura larvae.

Discussion

This is the first record of a natural infection of A. nomiae on insects. A. nomiae has the potential to be used as a dual biocontrol EPF because of its ability to not only kill a broad spectrum of insect pests directly but also induce resistance against phytopathogens via plant colonization.

Preparation and activity of sodium carboxymethyl cellulose (CMC-Na) and Metarhizium rileyi ZHKUMR1 composite membrane

Improving the adhesion capability of Metarhizium rileyi ZHKUMR1 on leaves enabled by the combination with Carboxymethyl Cellulose (CMCNa) materials is feasible to improve the utilization rate of Metarhizium rileyi. Herein, the CMC-Na-ZHKUMR1 membrane was prepared by simply mixing Carboxymethyl Cellulose (CMCNa) with Metarhizium rileyi. Through compatibility test, it was found that the inhibition rates of spore germination and mycelial growth of ZHKUMR1 were only 1.51 % and 3.13 % when the concentration of Carboxymethyl Cellulose (CMCNa) was 0.5 %. By adding 2 % of Carboxymethyl Cellulose (CMCNa) under UV irradiation for 30 min, the protective rate of spore germination of ZHKUMR1 was up to ~12.44 %, where the wettability on corn leaves was achieved and the retention of ZHKUMR1 spores on corn leaves was increased. After indoor activity determination, it was found that after 3 min of simulated rain washing, the lethal rate of corn leaves pretreated with CMC-Na-ZHKUMR1 on the 2nd instar larvae of Spodoptera frugiperda was 46.67 %, which was much higher than that of ZHKUMR1 spore suspension alone. This work clearly showed that Carboxymethyl Cellulose (CMCNa) effectively improved the field application effect of Metarhizium rileyi ZHKUMR1, and this strategy provided guidance for improving the field efficacy of Metarhizium rileyi ZHKUMR1.

Evaluation of the Insecticidal Potential of Heterotheca inuloides Acetonic and Methanolic Extracts against Spodoptera frugiperda and Their Ecotoxicological Effect on Poecilia reticulata

For the management of Spodoptera frugiperda, botanical extracts have been used to reduce the environmental impacts of synthetic chemical pesticides. In the present investigation, the insecticidal activity of the acetonic and methanolic extracts of Heterotheca inuloides (Asteraceae) and of the main compound 7-hydroxy-3,4-dihydrocadalene on this pest as well as its ecotoxicological effect on Poecilia reticulata were evaluated. A greater insecticidal response was obtained from the acetonic extracts than from the methanolic extracts, with LC50 values of 730.4 ppm and 711.7 ppm for samples 1 and 2, respectively. Similarly, there was a lethal effect on 50% of the P. reticulata population at low concentrations in the acetonic extract compared to the methanolic extract. The sesquiterpene 7-hydroxy-3,4-dihydrocadalene has greater insecticidal activity by presenting an LC50 of 44.36 ppm; however, it is classified as moderately toxic for guppy fish.

One stone for two birds: Endophytic fungi promote maize seedlings growth and negatively impact the life history parameters of the fall armyworm, Spodoptera frugiperda

The fall armyworm (FAW) Spodoptera frugiperda, is a voracious pest of cereals native to the Americas and which invaded Africa in 2016. Chemical control is the main management option, which however remains ineffective and unsustainable. Fungal endophytes are increasingly used as alternative for the management of insect pests of economic importance. This study assessed the potential of eight endophytic fungal isolates to colonize maize plant and their ability to promote seedlings growth through seed and foliar inoculations, as well as their suppressive effects on FAW. Fungal colonization rates of different plant parts by the endophytes varied as per the inoculation methods. Beauveria bassiana ICIPE 279 colonized more than 60% of all the seedling parts while B. bassiana G1LU3 only colonized stem (25%) and leaf (5%) tissues through foliar inoculation. Trichoderma atroviride F2S21, T. asperellum M2RT4, T. harzianum F2R41, Trichoderma sp. F2L41, Hypocrea lixii F3ST1 and Fusarium proliferatum F2S51 successfully colonized all the plant parts and therefore were selected and further evaluated through seed inoculation for their endophytic persistence, effect on plant growth, and pathogenicity to Spodoptera frugiperda immature and adult stages. Weekly assessment showed varied effect of the endophytes on maize plant growth parameters compared to the control. During the first week, percentage colonization of the plant parts ranges between 90%-100%, 65%-100%, and 60%-100%, in the roots, stems, and leaves, respectively for all the five tested isolates. However, the colonization pattern/rates significantly decreased over time for H. lixii F3ST1 in the stems and leaves, and for T. harzianum F2R41 in the leaves and for T. asperellum M2RT4 in the roots. In addition, T. harzianum F2R41 outperformed all the other isolates in boosting the plant height, whereas H. lixii F3ST1 and T. asperellum M2RT4 outperformed all the other isolates in increasing the wet and dry shoots weight. Furthermore, the number of egg masses laid on endophytically-colonized maize plants varied among the treatments. Trichoderma asperellum M2RT4 and H. lixii F3ST1 endophytically-colonized maize plants significantly reduced the number of egg masses and the defoliation/feeding rates of the pest compared to the control. Additionally, T. harzianum F2R41 had the highest negative impact on the pupation and adult emergence of S. frugiperda with a female-biased sex ratio. Our findings indicate that T. asperellum M2RT4, T. harzianum F2R41, and H. lixii F3ST1 hold a potential to be developed as endophytic-fungal-based biopesticides for sustainable management of S. frugiperda and as plant growth promoters.

New frontiers of soil fungal microbiome and its application for biotechnology in agriculture

The fungi-based technology provided encouraging scenarios in the transition from a conventionally based economic system to the potential security of sources closely associated with the agricultural sphere such as the agriculture. In recent years, the intensification of fungi-based processes has generated significant gains, additionally to the production of materials with significant benefits and strong environmental importance. Furthermore, the growing concern for human health, especially in the agriculture scenario, has fostered the investigation of organisms with high biological and beneficial potential for use in agricultural systems. Accordingly, this study offered a comprehensive review of the diversity of the soil fungal microbiome and its main applications in a biotechnological approach aimed at agriculture and food chain-related areas. Moreover, the spectrum of opportunities and the extensive optimization platform for obtaining fungi compounds and metabolites are discussed. Finally, future perspectives regarding the insurgency of innovations and challenges on the broad rise of visionary solutions applied to the biotechnology context are provided.

Tolerance to UV-B radiation of the entomopathogenic fungus Metarhizium rileyi

Soybean, corn, and cotton crops are afflicted by several noctuid pests and the development of bioinsecticides could help control these pests. The fungus Metarhizium rileyi has the greatest potential because its epizootics decimate caterpillar populations in the absence of insecticide applications. However, insect-pathogenic fungi when used for insect control in agriculture have low survival mainly due to the deleterious effects of ultraviolet radiation and heat from solar radiation. In this study, fourteen isolates of M. rileyi were studied and compared with isolates ARSEF 324 and ARSEF 2575 of Metarhizium acridum and Metarhizium robertsii, respectively, whose sensitivity to UV-B radiation had previously been studied. Conidia were exposed at room temperature (ca. 26 °C) to 847.90 mWm-2 of Quaite-weighted UV-B using two fluorescent lamps. The plates containing the conidial suspensions were irradiated for 1, 2, and 3 h, providing doses of 3.05, 6.10, and 9.16 kJ m2, respectively. A wide variability in conidial UV-B tolerance was found among the fourteen isolates of M. rileyi. Isolate CNPSo-Mr 150 was the most tolerant isolate (germination above 80% after 2 h exposure), which was comparable to ARSEF 324 (germination above 90% after 2 h exposure), the most tolerant Metarhizium species. The least tolerant isolates were CNPSo-Mr 141, CNPSo-Mr 142, CNPSo-Mr 156, and CNPSo-Mr 597. Nine M. rileyi isolates exhibited similar tolerance to UV-B radiation as ARSEF 2575 (germination above 50% after 2 h exposure). In conclusion, the majority of M. rileyi isolates studied can endure 1 or 2 h of UV-B radiation exposure. However, after 3 h of exposure, the germination of all studied isolates reduced below 40%, except for CNPSo-Mr 150 and ARSEF 324.

Blastospores from Metarhizium anisopliae and Metarhizium rileyi Are Not Always as Virulent as Conidia Are towards Spodoptera frugiperda Caterpillars and Use Different Infection Mechanisms

Infective conidia from entomopathogenic fungi are widely used to control insect pests. Many entomopathogenic fungi also produce yeast-like cells called blastospores under specific liquid culture conditions that can directly infect insects. However, little is known about the biological and genetic factors that allow blastospores to infect insects and make them potentially effective for biological control in the field. Here, we show that while the generalist Metarhizium anisopliae produces a higher number of and smaller blastospores, the Lepidoptera specialist M. rileyi produces fewer propagules with a higher cell volume under high-osmolarity conditions. We compared the virulence of blastospores and conidia of these two Metarhizium species towards the economically important caterpillar pest Spodoptera frugiperda. Conidia and blastospores from M. anisopliae were equally infectious, but acted slower, and killed fewer insects than M. rileyi conidia and blastospores did, where M. rielyi conidia had the highest virulence. Using comparative transcriptomics during propagule penetration of insect cuticles, we show that M. rileyi blastospores express more virulence-related genes towards S. frugiperda than do M. anisopliae blastospores. In contrast, conidia of both fungi express more virulence-related oxidative stress factors than blastospores. Our results highlight that blastospores use a different virulence mechanism than conidia use, which may be explored in new biological control strategies.

Trichoderma koningiopsis Survival on Coated Seeds and Effect on Plant Growth Promotion in Rice (Oryza sativa)

Seed coating is an alternative delivery system for beneficial plant microorganisms into the soil. Although seed coats are widely used for the application of agrochemicals, the incorporation of beneficial microorganisms has not been explored deeply and their survival on seeds while in storage is unknown. The study aimed to evaluate the effect of the coating process on microbial survival and on plant growth promotion. Two coating formulations were designed, and assessed by two coating processes: rotating drum and fluidized bed. The rotating drum process resulted in more uniform coatings than in the fluidized bed process. In addition, with this coating technique, lower viability losses over time were observed. The rotatory drum prototype containing a biopolymer and a clay mineral derivate (P90) showed the best behavior at the three temperatures evaluated, with superior viabilities compared to the other prototypes and the lowest loss of viability after 12 months. The formulation of this coating prototype may preserve the viability of Trichoderma koningiopsis Th003 up to 15 months at 8 °C, 9 months at 18 °C, and 3 months at 28 °C, which are very promising shelf-life results. Regarding the effect of seed coating on plant growth, prototypes showed higher yields > 16% than the control, comparable to the conventional use of Tricotec® WG, which may reduce the number of applications and water consumption for dissolution of the inoculant. The results demonstrated that the formulation composition, as well as the coating process may impact the microbial survival on seeds.

Potential Impact of Chemical Fungicides on the Efficacy of Metarhizium rileyi and the Occurrence of Pandora gammae on Caterpillars in Soybean Crops

Entomopathogenic fungi may play a crucial role in the regulation of caterpillar populations in soybean crops, either through natural occurrences or applied as mycopesticides. In the present work, we reported the naturally occurring entomopathogenic fungus Pandora gammae attacking the caterpillar Chrysodeixis includens, with infection rates in field trials ran in two consecutive years in the 10-35% range. As many chemicals are potentially harmful to entomopathogenic fungi, this work aimed to investigate the potential impact of two chemical fungicides (azoxystrobin + benzovindiflupyr and trifloxistrobina + prothioconazole) used to control soybean rust (Phakopsora pachyrhizi) on the natural occurrence of P. gammae and Metarhizium rileyi, as well as the efficacy of the latter fungus applied as different formulations against the soybean caterpillars Anticarsia gemmatalis and C. includens. Under laboratory conditions, fungicides used at field-recommended rates had a considerable negative impact on the germinability of M. riley on the medium surface, and all tested formulations did not protect conidia from damage by these chemicals. This harmful effect also impacted host infectivity, as the larval mortality owing to this fungus was reduced by 30-40% compared to that of the fungicide-free treatments. In field trials conducted in two subsequent years, unformulated and formulated M. rileyi conidia applied to soybean plants produced primary infection sites in caterpillar populations after a single spray. Spraying unformulated or formulated M. rileyi conidia following fungicide application on plants did not affect host infection rates over time. Moreover, the use of M. rileyi-based formulations or chemical fungicide did not interfere with the natural infection rates by P. gammae on its host, C. includens. Although a higher degree of exposure to non-selective fungicides can negatively affect fungal entomopathogens, a single foliar application of fungicides may be harmless to both M. rileyi and P. gammae in soybean fields. Additionally, this work showed that naturally occurring wasps and tachnids also play an important role in the regulation of A. gemmatalis and, notably, C. includens, with parasitism rates above 40-50% in some cases.

Infection of the entomopathogenic fungus Metarhizium rileyi suppresses cellular immunity and activates humoral antibacterial immunity of the host Spodoptera frugiperda

BACKGROUND

Metarhizium rileyi is an entomopathogenic fungus with promising potential for controlling agricultural pests, including Spodoptera frugiperda. Following penetration of the host through the cuticle, M. rileyi cells transform into in vivo blastospores or hyphal bodies, propagating within the hemocoel. However, the strategies and molecular mechanisms by which M. rileyi survives upon exposure to the powerful insect immune system remain unclear.

RESULTS

We determined the pathogenicity of M. rileyi and found that either conidial immersion or blastospore injection significantly decreased S. frugiperda survival in a dose-dependent manner. Injection of M. rileyi blastospores decreased the number of S. frugiperda hemocytes and impaired host cellular reactions such as nodulation, encapsulation and phagocytosis. Blastospore injection led to increased antibacterial activity in plasma at 48 h post-injection (hpi). RNA-sequencing analyses identified a large number of antimicrobial peptide genes upregulated in the fat body of M. rileyi-infected larvae at 48 hpi, which may be attributable to the activation of Toll and IMD signaling pathway.

CONCLUSION

This study demonstrates that the compromised cellular immunity of the insect host is due to the marked decrease in hemocytes and impaired cellular cytoskeletons, which may facilitate early infection by M. rileyi. Late in the course of infection, the enhanced antibacterial activity of plasma, which may be in response to intestinal evading bacteria, cannot inhibit hyphal growth in hemolymph. Our data provide a comprehensive resource for exploring the molecular mechanism employed by M. rileyi to overcome S. frugiperda immunity. © 2022 Society of Chemical Industry.

Assessment of a potential bioproduct for controlling Cerotoma arcuata tingomariana (Coleoptera: Chrysomelidae)

AIMS

The leaf-feeding pest Cerotoma arcuata tingomariana (Bechyné) (Coleoptera: Chrysomelidae) produces huge economic losses in different crops. This study aimed to produce conidia by semisolid-state fermentation and to establish the insecticidal activity of two formulation prototypes based on a native Beauveria bassiana isolate for controlling this pest.

METHODS AND RESULTS

A novel fabric-based semisolid-state fermentation strategy for quick and large-scale conidia production was performed and characterized. Conidia were formulated as an emulsifiable concentrate (EC) and a water-dispersible granulate (WG). Afterwards, the mortality of C. a. tingomariana adults was assessed. A conidia concentration of 2.9 x10⁹ conidia cm^-2 was obtained after nine days-course fermentation and a yield of 33.4 g kg^-1 dry-substrate.

CONCLUSIONS

The polyester fabric-based fermentation is an efficient technique for producing and collecting B. bassiana spores. Regarding LC₉₀ , the potency analysis showed that the EC was 21-fold more potent than the non-formulated conidia, and ~2.6-fold more potent than the WG.

SIGNIFICANCE AND IMPACT OF STUDY

A high throughput fermentation based on polyester fabric as support for B. bassiana conidia production and subsequent formulation as an EC comprises a promising strategy for obtaining a bioproduct to control adults of C. a. tingomariana and other Chrysomelidae pests.

Evaluation of key parameters for developing a Metarhizium rileyi-based biopesticide against Spodoptera frugiperda (Lepidoptera: Noctuidae) in maize: laboratory, greenhouse, and field trials

BACKGROUND

The entomopathogenic fungus Metarhizium rileyi is known to cause natural infections in some caterpillars. In this multiyear study, we carried out laboratory, greenhouse and three field trials with the aim of developing a sustainable option for control of the fall armyworm (FAW) in maize. Association of M. rileyi with Spodoptera frugiperda baculovirus (SfMNPV) and delivery strategies were also investigated.

RESULTS

The selected isolate (CG381) was effective in the laboratory at a low concentration (~ 4 × 10³  conidia cm^-2 ), killing >95% of FAW larvae within 8 days. In the greenhouse assay, applications of conidia suspended in water or as dry powder in maize whorls (~ 6.3 × 10⁶ conidia per plant) produced similar larval mortalities (88%-96%). In the field trials, conventional spraying of unformulated conidia (0.6 and 1.2 × 10¹² conidia ha^-1 ) caused low larval mortalities (27-31%). Simultaneous application of either unformulated or oil-based formulations of M. rileyi conidia and S. frugiperda baculovirus (SfMNPV) to plant rows caused larval mortalities comparable with each of the pathogens applied alone. However, when a formulation containing both pathogens was sprayed directly into the whorls, the overall mortality of S. frugiperda larvae due to pathogens (mostly to M. rileyi infections) reached ~ 59%, twofold higher than the other treatments with conventional spraying, whereas in the control, the overall mortality was only 1%.

CONCLUSION

Optimizing exposure of S. frugiperda larvae to an inoculum of virulent entomopathogens through directed applications to maize whorls is critical to produce satisfactory mortality levels and is promising for integrated pest management.

Field Efficacy of Metarhizium rileyi Applications Against Spodoptera frugiperda (Lepidoptera: Noctuidae) in Maize

The efficacy of the fungus Metarhizium rileyi (Farlow) Kepler, S. A. Rehner & Humber (Hypocreales: Clavicipitaceae) against the fall armyworm Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) and the impact on the community of epigeans predators as well as the natural occurrence of native fungal strains were evaluated after sequential sprays in maize. In the first season, the infestation was lower than 0.2 larvae per plant throughout the three fungal sprays and no significant difference was observed in the number of infected larvae among treatments. In the second season, insect population reached an average of 0.8 larvae per plant between the second and third sprays and the number of larvae succumbed by M. rileyi was higher in fungal-treated plots in the following weeks. Molecular characterization of the collected isolates on mummified larvae revealed the introduction of a new isolate did not eliminate the native strain on the fungal-treated plots. In both seasons, the diversity and abundance of predator species in the plots were not affected by any of the treatments. We showed that applications of selected strains of M. rileyi early in the season have no significant impact on the occurrence of natural enemies in maize.

Observations on the Relationships between Endophytic Metarhizium robertsii, Spodoptera frugiperda (Lepidoptera: Noctuidae), and Maize

Fungi in the genus Metarhizium are entomopathogens that can establish endophytically inside plants and benefit them through growth promotion and pest suppression. Lab- and greenhouse-based experiments were conducted to examine the effects of endophytic M. robertsii colonization in maize (Zea mays) on fall armyworm (FAW) (Spodoptera frugiperda). Maize seeds were inoculated with M. robertsii conidia, plants were evaluated for endophytic colonization, and then relative growth rate (RGR) and feeding behavior of larval FAW fed leaves from inoculated and uninoculated maize were measured. Endophytic M. robertsii was recovered from 60.5% of inoculated maize. In feeding bioassays, the RGR of larval FAW fed leaves of inoculated maize was no different than the RGR of larvae fed leaves from uninoculated maize. The RGR of larval FAW was positively correlated with the proportion of endophytic colonization of maize leaf and root tissues; however, in feeding assays, FAW larvae demonstrated no preference for consuming leaf tissue from inoculated or uninoculated maize. The proportion of leaf tissue consumed was unrelated to the proportion of M. robertsii-colonization of leaf or root tissue from source plants. We discuss possible reasons why FAW were not affected by endophytic M. robertsii in the context of assay methodology, FAW physiology, and induced maize defenses.

Secondary screening of strains of antagonists to a Phoma pathogen on sunflower

There are presented data of the first stage of the secondary screening of antagonist strains from a collection of the biological methods laboratory of V.S. Pustovoit All-Russian Research Institute of Oil Crops to the aggressive isolate of Phoma macdonaldii Boerema infecting sunflower. We used methods of ‘agar blocks’ and ‘perforated Petri dishes’. As a result of a screening of 55 antagonist strains to Phoma macdonaldii pathogen we selected 17 promising strains-producers of microbiological preparations having biological efficiency exceeding 40.0 %. In control variant without seed treatment sunflower seedlings infection was up to 76.2 %, and maximal biological efficiency of laboratory samples from fungi-producers were determined for a strain M-24 Penicillium sp. (73.8 %); from bacteria of a genus Bacillus – for a strain D-10 Bacillus sp. (74.2%); from bacteria of a genus Pseudomonas – for a strain Sgc-1 Pseudomonas sp. (73.8 %). Maximal colonizing activity were noted for fungi-producers M-24 Penicillium sp. (85.7 %) and Xk-1 Ch. olivaceum (71.4 %), as well as for bacteria of a genus Bacillus – 5B-1 B. subtilis (71.4 %) and a genus Pseudomonas – Oif 2-1 Pseudomonas sp. and 14-3 P. chlororaphis (71.4 %) against Phoma infection in control of 70.0 %.

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.