Entomopathogenic fungi, plasma-activated water, and their synergistic effects for sustainable management of Lipaphis erysimi.

Abstract

Entomopathogenic fungi (EPF) are widely recognized as effective and environmentally sustainable biological control agents for a broad spectrum of agricultural insect pests. The increasing complexity and intensification of contemporary agricultural systems require the identification and development of more virulent and resilient fungal strains to ensure consistent pest suppression. In this study, ten EPF isolates representing Beauveria bassiana, Cordyceps javanica, and Metarhizium anisopliae were selected based on preliminary laboratory screens, and the insecticidal effectiveness of these isolates was tested against the mustard aphid, Lipaphis erysimi, along with the direct and interactive effects of plasma-activated water (PAW). Here, the PAW was generated using a surface dielectric barrier discharge (sDBD) plasma system, producing highly acidic water enriched with reactive oxygen and nitrogen species. Direct and daily application of PAW at concentrations of 50, 100, and 1,000 ppm resulted in complete aphid mortality within seven days at all tested concentrations. Conidial germination assays showed that lower PAW concentrations had less effect, whereas higher concentrations significantly inhibited germination. In certain isolates, the combined application of 100 ppm PAW and EPF produced greater aphid control than single EPF treatments. Overall, a single application of EPF achieved 87.67% aphid control, whereas the combined treatment achieved 99.67% mortality. Based on Lethal Time (LT₅₀) values, C. javanica SLLC-Cj 24 (single application average 6.93 days; combined application average 6.60 days) was the most virulent strain, followed by SLLC-Cj 11 (single application average 7.17 days; combined application average 6.65 days). Among the tested fungal strains, B. bassiana SLLC-Bb 12 demonstrated the strongest synergistic interaction with PAW, followed by C. javanica SLLC-Cj 1. These findings demonstrate that PAW possesses intrinsic insecticidal activity and can enhance overall mortality when integrated with EPF. However, isolate- or strain-specific interactions may influence mortality and infection rates, highlighting the need to select fungal cultures, optimize concentration, and exposure parameters for synergistic biocontrol strategies.