Screen bag formulation of Beauveria and Metarhizium granules to manage Riptortus pedestris (Hemiptera: Alydidae)

Most entomopathogenic fungal biopesticides have been produced in wettable powder and liquid concentrate formulations. Separation of fungal conidia from granular substrates to manufacture these formulations is costly and labor-intensive, which has hampered growth of the fungal biopesticide industry. Herein to overcome this challenge, we developed a novel screen bag formulation using mycotized granules produced from solid-substrate cultures of Beauveria bassiana JEF-007 and Metarhizium anisopliae JEF-003. The isolates were solid-cultured on Italian millet grains and packed in screen bags (pore size: ~ 15 μm). The bags containing the mycotized granules were immersed in water and agitated to disperse the conidia, after which the number of conidia released into the water was determined. These results were compared to the number of conidia released after vortexing the granules in water as a control. Various surfactants were added to the water to assess their effect on conidial release. Silwet L-77 yielded the highest conidial release. The insecticidal activity against Riptortus pedestris nymphs of suspensions produced from the screen bag formulation and vortexed conidial suspensions was similar, demonstrating that our novel formulation could be a cost-effective replacement for standard WP and ES formulations. The screen bag formulation has several advantages over other standard fungal-based formulations, such as a shorter and lower-cost production process. This formulation technology could also be applied to other conidial-based biopesticides, such as fungal fungicides, herbicides, and fertilizers.