Laboratory Assessment of Plant Losses by Sphenarium purpurascens and Control with Entomopathogenic Fungi in Oil Emulsions

This study addresses the agricultural impact of the grasshopper Sphenarium purpurascens and evaluates the efficacy of entomopathogenic fungi (EPF), Beauveria bassiana, and Metarhizium robertsii, formulated in vegetable oil emulsions as sustainable pest control agents. The losses caused by S. purpurascens at different developmental stages (N4, N5, and adult) were assessed in five economically significant crops (Medicago sativa, Zea mays, Helianthus sp., Cynodon dactylon, and Cucurbita pepo), revealing a marked preference for Helianthus sp. and C. pepo, with consumption rates reaching 0.92 g/48 h during N4 and N5 stages, while adults showed preference for M. sativa (1.18 g/48 h) and Z. mays (1.15 g/48 h). The viability of EPF in oil emulsions (20% and 40% concentrations) was evaluated, demonstrating that formulations with Azadirachta indica and Moringa oleifera maintained over 99% fungal viability compared to the control absolute with distilled water (DW). The effectiveness of EPF against S. purpurascens adults was tested, with EPF on M. robertsii combined with Persea americana achieving 100% mortality within 72 h. Finally, the pathogenicity and dispersion of EPF in oil emulsions were evaluated, demonstrating that, at 240 h, the B. bassiana + A. indica strain (with three inoculated insects) achieved 100% mortality. It was observed that the number of inoculated adults directly influenced the mortality of S. purpurascens. These findings highlight the potential of EPF as a sustainable pest management strategy, emphasizing the need for further field trials to optimize its application and mitigate agricultural losses caused by S. purpurascens.