The spread of the slant-face grasshopper, known as Acrida conica, has recently caused substantial economic damage. Metarhizium anisopliae var. acridum is the most common entomopathogenic fungi which used as biological agents, they provide a safer and more efficient substitute for conventional insecticides. The study was conducted on A. conica nymphs in the Bahariya Oases, Egypt, during the summer season (2025) utilizing a sunflower oil based ultra-low volume (ULV) and water based low volume (LV) spray techniques. Mortality rates, median lethal time (LT₅₀), and haemolymph biochemical disruptions were studied.

The sunflower oil based ULV greatly increased fungal virulence, according to the results, which showed 96.4% nymphal mortality at 10 days post-treatment compared to 76% by water based LV application. It also achieved LT₅₀ of 4.17 and slope 3.24, while water based LV had LT₅₀ 6.12 and slope 2.18 indicating quicker fungal activity. Biochemical assessments performed five days after treating the fifth nymphal instar of A. conica with a sunflower oil based ULV application confirmed a severe metabolic collapse, reflected by a -63.9% decline in trehalase enzyme activity, indicating severe energy depletion. Lactate dehydrogenase (LDH), chitinase, and protease enzymes were all strongly activated, with increases of +237.5%, +413.1%, and +186.9% more than control, respectively.