Persistence of Isaria fumosorosea (Hypocreales: Cordycipitaceae) SFP-198 Conidia in Corn Oil-Based Suspension

Increased Attraction and Stability of Beauveria bassiana-Formulated Microgranules for Aedes aegypti Biocontrol

Aedes aegypti (Linn.) incidence has increased in recent years, causing human viral diseases such as dengue, which are often fatal. Beauveria bassiana (Bals., Vuillemin) efficacy for Ae. aegypti biological control has been evidenced but it relies on host susceptibility and strain virulence. We hypothesized that B. bassiana conidia microgranular formulations (MGF) with the additives acetone, lactic acid, and sugar increase Ae. aegypti adult exposure, thus improving their biocontrol effectiveness. Beauveria bassiana strain four (BBPTG4) conidia stability was assessed after 0 d, 5 d, and 30 d storage at 25 °C ± 2 °C with additives or in MGF after 91 d of storage at 25 °C ± 2 °C or 4 °C ± 1 °C, whereas mortality was evaluated after adult exposure to MGF + conidia, using home-made traps. Additives did not show toxicity to conidia. In addition, we observed that sugar in MGF increased Ae. aegypti adults’ attraction and their viability resulted in a 3-fold reduction after 5 d and 1- to 4-fold decrease after 30 d of storage, and formulations were less attractive (p < 0.05). Conidia stability was higher on MGF regardless of the storage temperature, losing up to 2.5-fold viability after 91 d. In conclusion, BBPTG4 infected and killed Ae. aegypti, whereas MGF attracting adults resulted in 42.2% mortality, increasing fungus auto dissemination potential among infected surviving adults. It is necessary to further evaluate MGF against Ae. aegypti in the field.

Selection and characterization of thermotolerant Beauveria bassiana isolates and with insecticidal activity against the cotton-melon aphid Aphis gossypii (Glover) (Hemiptera: Aphididae)

BACKGROUND

Cotton-melon aphid Aphis gossypii (Glover) causes severe damage mainly to cucurbits. Twenty-two Beauveria sp. isolates were simultaneously assessed for their pathogenicity and heat tolerance. The selected isolates were identified molecularly and characterized in terms of conidial germination rate, mycelial growth, conidial yield and endophytic activity.

RESULTS

Screening bioassays showed that the B. bassiana isolates B3, B7, B9 and B12 were the most toxic, inducing mortality equal to or slightly higher than the commercialized strain B. bassiana BNat (70.7%). Median lethal concentration (LC₅₀ ) bioassays revealed that only isolate B12 had a significantly lower LC₅₀ value (5.4 × 10⁵ conidia ml^-1 ) than strain BNat (5 × 10⁶ conidia ml^-1 ). The heat tolerance screening test (1 h of exposure to 45°C) allowed us to select isolates B3, B7, B9 and B12 with germination rates of 57.5% to 80.1% after 24 h incubation at 25°C, all significantly higher than strain BNat (22.1%). The germination rates of all isolates decreased significantly after 2 h of exposure to 45°C, with the exception of isolate B12 which displayed the highest thermotolerance (72% germination). The four selected isolates were able to endophytically colonize cucumber leaves when applied to the foliage. Inoculation of cucumber plants with isolate B12 did not affect cucumber plant growth. However, several plant growth parameters were improved 5 weeks after root inoculation.

CONCLUSION

On the basis of its potent toxicity and thermotolerance, isolate B12 is a good candidate for further development as a biopesticide for use in integrated pest management strategies for aphid control. © 2022 Society of Chemical Industry.

Production of Microsclerotia by Metarhizium sp., and Factors Affecting Their Survival, Germination, and Conidial Yield

Microsclerotia (MS) produced by some species of Metarhizium can be used as active ingredients in mycoinsecticides for the control of soil-dwelling stages of geophilic pests. In this study, the MS production potential of two Metarhizium brunneum strains and one M. robertsii strain was evaluated. The three strains were able to produce MS in liquid fermentation, yielding between 4.0 × 106 (M. robertsii EAMa 01/158-Su strain) and 1.0 × 107 (M. brunneum EAMa 01/58-Su strain) infective propagules (CFU) per gram of MS. The EAMa 01/58-Su strain was selected for further investigation into the effects of key abiotic factors on their survival and conidial yield. The MS were demonstrated to be stable at different storage temperatures (−80, −18, and 4 °C), with a shelf-life up to one year. The best temperature for MS storage was −80 °C, ensuring good viability of MS for up to one year (4.9 × 1010 CFU/g MS). Moreover, soil texture significantly affected CFU production by MS; sandy soils were the best driver of infective propagule production. Finally, the best combination of soil temperature and humidity for MS germination was 22.7 °C and 7.3% (wt./wt.), with no significant effect of UV-B exposure time on MS viability. These results provide key insights into the handling and storage of MS, and for decision making on MS dosage and timing of application.

Entomopathogenic Fungi for Pests and Predators Control in Beekeeping

The emergence of resistance to chemical drugs in beekeeping is becoming a phenomenon of widespread concern. One promising alternative to the use of chemicals is entomopathogenic organisms that are environmentally friendly and are capable of stopping the expression of resistance once it has evolved. In the recent past, the scientific community has carried out several experiments addressing the use of microbiological control agents. In particular, experimental studies using entomopathogenic fungi have had more success in honey bee research. With their adherence properties and their ability to digest the cuticle and overcome the host defense mechanism, they could be a suitable ingredient in bioacaricides. Several promising fungi have been identified in the search for effective means to control pest populations. The data obtained from the different experiments are interesting and often favorable to their use, but there are also conflicting results. The aim of this review is to describe the state of the art on the topic under investigation.

Insect-fungal-interactions: A detailed review on entomopathogenic fungi pathogenicity to combat insect pests

Global food security is threatened by insect pests of economically important crops. Chemical pesticides have been used frequently for the last few decades to manage insect pests throughout the world. However, these chemicals are hazardous for human health as well as the ecosystem. In addition, several pests have evolved resistance to many chemicals. Finding environment friendly alternatives lead the researchers to introduce biocontrol agents such as entomopathogenic fungi (EPF). These fungi include various genera that can infect and kill insects efficiently. Moreover, EPFs have considerable host specificity with a mild effect on non-target organisms and can be produced in bulk quantity quickly. However, insights into the biology of EPF and mechanism of action are of prime significance for their efficient utilization as a biocontrol agent. This review focuses on EPF-mediated insect management by explaining particular EPF strains and their general mode of action. We have comprehensively discussed which criteria should be used for the selection of pertinent EPF, and which aspects can impact the EPF efficiency. Finally, we have outlined various advantages of EPF and their limitations. The article summarizes the prospects related to EPF utilization as biocontrol agents. We hope that future strategies for the management of insects will be safer for our planet.

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

The insect-pathogenic fungus Metarhizium rileyi is highly sensitive to nutritional and environmental conditions which makes it difficult to produce as a stable biopesticide. In this study, a Colombian isolate of this fungus was produced in bulk, and conidia were formulated as an emulsifiable concentrate (EC). The stability of formulated conidia was studied. Conidial viability was maintained at >85 % viability for 12 m under refrigeration and for >three months at 18 °C. The pH values were stable, while contaminant content was significantly reduced. The efficacy of the EC to control Spodoptera frugiperda (Smith) was correlated with the storage time using different mathematical models, and conservative values of six and 12 months at 8 °C and 18 °C respectively, were established. Finally, the EC was evaluated in maize plants under glasshouse conditions. The LC₅₀ and LC₉₀ were estimated to be 1.17 × 10⁴ and 4.03 × 10⁶ conidia/mL respectively and a 57 % reduction in recent damage of plants was achieved. This study demonstrated the potential of M. rileyi formulated as EC to control S. frugiperda in maize. Therefore, it is necessary to continue developing this biopesticide, in order to deliver a new tool to be integrated in pest management programs.

An oil-based formulation of Isaria fumosorosea blastospores for management of greenhouse whitefly Trialeurodes vaporariorum (Homoptera: Aleyrodidae)

BACKGROUND

To date, emphasis has been placed on studying the virulence of Isaria fumosorosea conidia rather than the virulence of their blastospores. In the present study, a comparison was made of the efficacy of blastospores of I. fumosorosea (SFP-198) versus conidia against greenhouse whitefly (GWF) Trialeurodes vaporarioum nymphs and thermotolerance at 50 °C. To improve thermotolerance and potency, the blastospores were suspended in corn oil with a wetting and an insect-filming agent.

RESULTS

Blastospores had similar efficacy against GWF nymphs to conidia in glasshouse conditions but had less thermotolerance than conidia. However, blastospores in corn oil had increased thermotolerance, comparable with that of conidia in corn oil. Application of SFP-198 blastospore oil-based formulation containing isotridecyl alcohol ethoxylated-3EO (TDE-3) and sodium alginate (SA) as adjuvants showed enhanced efficacy (95.7% mortality), compared with the SA-free oil formulation (72.8%) in 10 days.

CONCLUSION

SFP-198 blastospores can be used as an effective biological control agent, given their virulence against GWF, the enhanced thermotolerance in corn oil and the oil-based formulation studies to enhance their efficacy. Blastospores can be easily produced in liquid cultures in less than 4 days, which is significantly shorter than using traditional solid cultures for conidial production.

Production of thermotolerant entomopathogenic fungal conidia on millet grain

Thermotolerance of entomopathogenic (insect-killing) fungi should be seriously considered before industrialization. This work describes the feasibility of millet grain as a substrate for production of thermotolerant Beauveria bassiana (Bb) GHA and ERL1170 and Metarhizium anisopliae (Ma) ERL1171 and ERL1540 conidia. First, conidial suspensions of the Bb isolates, produced on millet grain in polyethylene bags, were exposed to five temperatures (43-47 °C) at 15-min intervals for up to 120 min (experiment I). Agar-based quarter-strength (¼) Sabouraud dextrose agar supplemented with yeast extract (SDAY) and whey permeate media served as controls. Millet-grain-based culture was superior in producing the most thermotolerant Bb conidia, followed by whey permeate agar and ¼SDAY-based cultures. Secondly, to compare the thermotolerance of conidia produced at the same conditions, the Bb isolates were then produced on agar-based millet powder medium, with ¼SDAY and whey permeate agar media as controls, and the two Ma isolates were added (experiment II). They were then exposed to the same temperatures as above. More thermotolerant Bb and Ma conidia were produced on millet powder agar than on whey permeate agar and ¼SDAY overall. These results suggest that millet grain can be used as a substrate to produce thermotolerant conidia in a mass production system.