Silver nanoparticles are widely used in the biomedical and agri-food fields due to their versatility. The use of biological methods for the synthesis of silver nanoparticles has increased considerably due to their feasibility and high biocompatibility. In general, microorganisms have been widely explored for the production of silver nanoparticles for several applications. The objective of this work was to evaluate the use of entomopathogenic fungi for the biological synthesis of silver nanoparticles, in comparison to the use of other filamentous fungi, and the possibility of using these nanoparticles as antimicrobial agents and for the control of insect pests. In addition, the in vitro methods commonly used to assess the toxicity of these materials are discussed. Several species of filamentous fungi are known to have the ability to form silver nanoparticles, but few studies have been conducted on the potential of entomopathogenic fungi to produce these materials. The investigation of the toxicity of silver nanoparticles is usually carried out in vitro through cytotoxicity/genotoxicity analyses, using well-established methodologies, such as MTT and comet assays, respectively. The use of silver nanoparticles obtained through entomopathogenic fungi against insects is mainly focused on mosquitoes that transmit diseases to humans, with satisfactory results regarding mortality estimates. Entomopathogenic fungi can be employed in the synthesis of silver nanoparticles for potential use in insect control, but there is a need to expand studies on toxicity so to enable their use also in insect control in agriculture.

Entomopathogenic fungi are microbial agents of insect control in nature. They have been used as biologic strategies to manage insect invasion; however, the challenge is to maintain their shelf life and viability when exposed to high temperatures, ultraviolet radiation, and humidity. Synthesized silver nanoparticles (AgNPs) from fungal extracellular enzymes are an alternative using these microorganisms to obtain nanoparticles with insecticidal action. The present study evaluates the biomass production and the potential to synthesize silver nanoparticles using entomopathogenic fungi isolates. Sixteen isolates of entomopathogenic fungi were used in this study. The fungi pathogenicity and virulence were evaluated using the insect model Tenebrio molitor, at a concentration of 5 × 106 conidia/mL. The fungal biomass was produced in a liquid medium, dried, and weighed. The synthesis of silver nanoparticles was performed with aqueous extracts of the entomopathogenic fungi and silver nitrate solution (1 mM), following characterization by a UV/vis spectrophotometer, mean size, and polydispersity index. The results showed a significant variation in pathogenicity, virulence, and biomass production among the evaluated fungi isolates; however, only one of the isolates did not have the potential to synthesize silver nanoparticles. Pearson’s correlation showed significant correlation values only between virulence ´ biosynthesis potential and biomass production ´ biosynthesis potential, both with negative values, indicating an inverse correlation. Thus, AgNPs with entomopathogenic fungus extract can produce an innovative bioinsecticide product using a green production process.

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The insect Plutella xylostella is known worldwide to cause severe damage to brassica plantations because of its resistance against several groups of chemicals and pesticides. Efforts have been conducted to overcome the barrier of P. xylostella genetic resistance. Because of their easy production and effective insecticidal activity against different insect orders, silver nanoparticles are proposed as an alternative for agricultural pest control. The use of entomopathogenic fungi for nanoparticle production may offer additional advantages since fungal biomolecules may synergistically improve the nanoparticle’s effectiveness. The present study aimed to synthesize silver nanoparticles using aqueous extracts of Beauveria bassiana, Metarhizium anisopliae, and Isaria fumosorosea isolates and to evaluate their insecticidal activity against P. xylostella, as innovative nano-ecofriendly pest control. The produced silver nanoparticles were evaluated by measuring the UV–vis spectrum and the mean particle size by dynamic light scattering (DLS). I. fumosorosea aqueous extract with 3-mM silver nitrate solution showed the most promising results (86-nm mean diameter and 0.37 of polydispersity). Scanning electron microscopy showed spherical nanoparticles and Fourier-Transform Infrared Spectroscopy revealed the presence of amine and amide groups, possibly responsible for nanoparticles’ reduction and stabilization. The CL50 value of 0.691 mg mL−1 was determined at 72-h for the second-instar larvae of the P. xylostella, promoting a 78% of cumulative mortality rate after the entire larval stage. From our results, the synthesis of silver nanoparticles mediated by entomopathogenic fungi was successful in obtaining an efficient product for insect pest control. The I. fumosorosea was the most suitable isolate for the synthesis of silver nanoparticles contributing to the development of a green nanoproduct and the potential control of P. xylostella.

The objective of this work was to evaluate the potential of the essential oils of the LGRA-106 and LGR A-108 Lip pia g racili s genot y pes for the control of diamondback moth (Plutella xylostella). The lethal concentrations (LCs) were estimated by two routes of action (residual and spraying), using oil concentrations ranging from 0.5 to 3.0% v v−1, diluted in Tween 80 (1.5%). To determine the effect of the LC to 50% (LC50) on the development of P. xylostella, two compounds of the L. gracilis genotypes, thymol, and carvacrol, were sprayed on the insects. The repellency of the LC50 was evaluated by residual action, in a free-choice behavioral bioassay. The LGRA-106 genotype showed a greater toxicity via residual action (LC50 = 8.82 mg mL−1), as well as a higher repellency index. LGRA-108 was more toxic via spraying (LC50= 9.64 mg mL−1). Larval development and viability were reduced in approximately 50% with LGRA-106 or thymol and up to 70% with LGRA-108 or carvacrol, which caused mortality from 1.70 to 1.97 days after spraying. The oils of the LGRA-106 and LGRA-108 genotypes of L. gracilis have insecticidal activity in the control of P. xylostella.

Description of the subject. This study describes development of mycoinsecticide formulations containing dry conidia of the entomopathogenic fungus Beauveria bassiana combined with various inert excipients in tablet form to facilitate conidia dispersion in water and to maintain viability during storage. Objectives. This study aimed to evaluate the tablet formation of B. bassiana conidia associated with different inert excipient under direct compression in a hydraulic press. Method. Evaluation and validation of the mechanical and storage properties of conidial tablets in different types of packaging. Results. The tablet formulation containing 30% conidia (active ingredient) and 70% cornstarch (inert excipient) displayed satisfactory results regarding mechanical resistance and dispersion in water. This tablet exhibited hardness and friability of 173.94 N and 0.34%, respectively. The tablet disintegration rate in water occurred in 2 min, presenting a rapid dispersion of 109 conidia∙ml-1. Tablet stored in polyethylene pot with polymerized silica exhibited viability ≥ 80% over 180 days storage (25-28 °C). Conclusions. The formulation-packaging binomial is promising, considering the physical-chemical tablet parameters and the viability data. The conidia:cornstarch tablet type formulation provides a relevant cost-benefit ratio of a simple production process of a bioinsecticide, besides the use of low-cost adjuvant and packaging (polyethylene pot). Considering that most biopesticide products require storage under refrigeration, this work becomes important since the formulation remained viable for 180-days storage under room temperature conditions.

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