Improving fungal biocontrol of Bactrocera dorsalis through binary strain combinations and UV-protective humate formulations.

BACKGROUND: The oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), is a destructive pest in the global fruit and vegetable industry. Current management relies heavily on synthetic chemical insecticides, which leads to resistance and environmental risks. Entomopathogenic fungi (EPF) are regarded as promising alternatives to chemical pesticides, but their use against B. dorsalis is constrained by stage-dependent efficacy and poor UV persistence. RESULTS: Twelve fungal isolates were screened against mature larvae, pupae and adults of B. dorsalis. Metarhizium guizhouense WN_M2 showed the most consistent virulence across the three stages, with corrected mortality of 70.2%, 43.6% and 100%, respectively. Three lead isolates, M. guizhouense WN_M1 and WN_M2 and Beauveria bassiana DF_B1, were selected for binary combination assays. Binary combinations enhanced efficacy against subterranean stages. At 1 × 108 conidia mL-1, DF_B1 + WN_M2 caused 92.86% corrected mortality in mature larvae and 75.31% in pupae. Among the UV-protective additives tested, potassium humate (HA-K) was the most effective, maintaining 86.9% conidial germination at 24 h after 6 h UV-B exposure, compared with 34.6% in the unprotected UV-B control. HA-K also helped preserve fungal pathogenicity against adults under UV-B stress. CONCLUSION: Binary combinations enhanced fungal virulence against subterranean stages, and HA-K improved conidial UV tolerance. These findings provide a promising basis for the further development of fungal biocontrol strategies to sustainably manage this pest. © 2026 Society of Chemical Industry.