The enhanced infectivity of Metarhizium flavoviride in oil formulations to desert locusts at low humidities

Summary Formulation in non‐evaporative diluents such as oils is required to exploit the advantages of controlled droplet application methods for biopesticides based on conidial suspensions of entomopathogenic fungi. In laboratory assays on desert locusts ( Schistocerca gregaria ), formulations of Metarhizium flauoviride conidia in cotton seed oil showed superior performance to water‐based suspensions and this was especially pronounced at low humidities (35% r.h.). The LD 50 s for oil and water suspensions at 5 days were 8900 and > 10 6 conidia/insect respectively. The dose‐mortality regression line for oil was more than four times steeper and median lethal times were typically 76% of those for aqueous suspensions. Formulation in oil improves the efficacy of this fungus and may extend the application of species with lipophilic conidia into less humid agricultural environments.