Leaf penetration by endophytic Metarhizium brunneum enables infection of Phthorimaea absoluta in tomato mines while inducing the crop defense system.

BACKGROUND: The endophytic entomopathogenic fungus Metarhizium brunneum Petch EAMa 01/58-Su shows strong potential for managing Phthorimaea absoluta, a major tomato pest. We evaluated this strain at the threshold-recommended application time on heterogeneous populations, covering pre- and post-mining stages and individuals arriving after treatment to assess its protective effect against subsequent infestations. RESULTS: Pre-mine sprays caused up to 36% total mortality and significantly reduced larval survival, gallery formation and adult emergence. Post-mine sprays reached 78.12% mortality, shortened pupal duration, reduced adult emergence and resulted in post-mortem sporulation. At 9 days post inoculation (DPI), histology revealed intercellular colonisation of tomato leaves and systemic infection of P. absoluta larvae within mines. In plants sprayed prior to infestation, females showed a slight preference for treated plants and minor larval penetration at 2 DPI. Despite this early behavioural response, long-term effects were evident, and total mortality reached 28.6% at 2 DPI and 31.3% at 14 DPI, indicating induced systemic resistance (ISR) activation supported by marked induction of ethylene/jasmonic acid-related genes (SlACO1, SlACS6, SlERF1, SlAOS2, SlOPR3 and SlWRKY70), despite only trace fungal DNA in distal tissues. CONCLUSION: Our results provide the first evidence that endophytic M. brunneum can penetrate tomato leaves and directly infect P. absoluta larvae within mines, while simultaneously priming systemic defences (ISR). This dual mode of action complements activity against pre- and post-mining stages and may contribute to protection against subsequent reinfestations, supporting the incorporation of this strain into P. absoluta integrated pest management programmes. © 2026 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.