Surfactant Compatibility Screening Improves Formulation Performance of Metarhizium anisopliae for Control of the Tomato Leafminer Phthorimaea absoluta

The tomato leafminer, Phthorimaea absoluta (Meyrick), is one of the most destructive pests of tomato worldwide, and its management is increasingly constrained by insecticide resistance and the pest’s concealed feeding behavior. Entomopathogenic fungi such as Metarhizium anisopliae represent promising biological alternatives; however, the hydrophobic nature of fungal conidia often limits their dispersibility and field performance. In this study, the compatibility of M. anisopliae strain QLSMA201102 with 21 commercial surfactants was systematically evaluated to identify formulation additives that improve conidial performance without compromising fungal viability. Surfactants representing four classes (non-ionic, anionic, biosurfactant, and silicone-based) were screened for their effects on conidial germination, mycelial growth, foliar adherence, dispersibility, environmental stress tolerance, and insecticidal activity against P. absoluta. Several anionic surfactants strongly inhibited conidial germination, whereas PEG-8000, Tween-80, and the biosurfactant SL maintained high viability and significantly improved conidial dispersibility and foliar retention. PEG-8000 provided the strongest protection against UV radiation (>90% germination after UV-A exposure), while SL enhanced the thermotolerance of conidia. In larval bioassays, formulations containing SL, PEG-8000 and Tween-80 significantly increased mortality of P. absoluta to 91.49%, 91.66% and 91.57%, respectively, compared to 65.71% for the surfactant-free control conidia. Overall, these results identify PEG-8000, Tween-80, and SL as promising formulation additives for improving the stability and efficacy of M. anisopliae-based biopesticides. This work provides a foundation for developing optimized fungal formulations to support sustainable integrated pest management of P. absoluta.