Characterization of a Biofilm Bioreactor Designed for the Single-Step Production of Aerial Conidia and Oosporein by Beauveria bassiana PQ2

Beauveria bassiana is an entomopathogenic fungus that is used for the biological control of different agricultural pest insects. B. bassiana is traditionally cultivated in submerged fermentation and solid-state fermentation systems to obtain secondary metabolites with antifungal activity and infective spores. This work presents the design and characterization of a new laboratory-scale biofilm bioreactor for the simultaneous production of oosporein and aerial conidia by B. bassiana PQ2. The reactor was built with materials available in a conventional laboratory. KLa was determined at different air flows (1.5–2.5 L/min) by two different methods in the liquid phase and in the exhaust gases. The obtained values showed that an air flow of 2.5 L/min is sufficient to ensure adequate aeration to produce aerial conidia and secondary metabolites by B. bassiana. Under the conditions studied, a concentration of 183 mg oosporein per liter and 1.24 × 109 spores per gram of support was obtained at 168 h of culture. These results indicate that the biofilm bioreactor represents a viable alternative for the production of products for biological control from B. bassiana.

Susceptibility and development of resistance of the mite Tetranychus urticae to aerial conidia and blastospores of the entomopathogenic fungus Beauveria bassiana

The virulence of aerial conidia of the entomopathogenic fungi Beauveria bassiana (Balsamo-Crivelli) Vuillemin (Hypocreales: Cordycipitaceae) has been documented on a very broad range of arthropods; however, the activity of blastospores against the two-spotted spider mite has been seldomly reported. Moreover, studies investigating the activity of blastospores under greenhouse conditions were not found in the literature. In this study, we tested the efficacy of blastospores and aerial conidia of two B. bassiana strains, against all life stages of Tetranychus urticae Koch (Acari: Tetranychidae). The concentration of 109 blastospores/ml of the Lebanese strain was the most efficient in laboratory experiments, and the recorded mortalities were 52, 67.9 and 95.3% in treated eggs, motile juveniles and adults, respectively. In greenhouse experiments, higher T. urticae mortalities were recorded among strawberry plants (Fragaria x ananassa) sprayed with blastospores of B. bassiana. Furthermore, the latter plants also recorded a higher yield (454.92 ± 5 g/plant) compared to infested control plants (144.42 ± 5 g/plant) during the growing season. In addition, this study also investigated for the first time the resistance development of T. urticae to different types of infective propagules of B. bassiana. Under selective pressure for 40 generations, the laboratory yielded aerial conidia (AC-TSM) and blastospores (BS-TSM) resistant strains of the mite recorded 28.8- and 8.4- fold change in LC50 values respectively when compared to the field strain; however, this resistance ratio was minimal when compared to those of chemical acaricides.

Virulence of Aerial Conidia of Beauveria bassiana Produced under LED Light to Ctenocephalides felis (Cat Flea)

Ctenocephalides felis is an ectoparasitic flea species commonly found on dogs and cats. The current study verified the in vitro virulence of conidia of the entomopathogenic fungus Beauveria bassiana produced under different color LED light (red, blue, purple, green, yellow, and white) to adults of C. felis. The fungal isolates were cultivated on malt extract agar (MEA). Bioassay treatments used aerial conidia in test tubes. Adult fleas were obtained from a house cat in Chiang Mai province, Thailand. The experiments were composed of one control and eleven treatment groups. All of the treatments with B. bassiana conidia caused adult mortality after an exposure of 12 h. Among the conditions used in this study, B. bassiana cultured under red LED and fluorescent light were the most effective in causing mortality (100 %) in adult fleas after 36 h. The experimental results indicate that these aerial conidia of B. bassiana have promising potential for use in control of C. felis adult stages.