Beauveria bassiana-based management of Thrips palmi in greenhouse

Thrips palmi Karny (melon thrips) damages over 200 plant species through direct feeding and vectoring tospoviruses. Excessive use of pesticides has led to melon thrips resistance development, necessitating the exploration of sustainable alternative control options. Entomopathogenic fungi (EPFs) can potentially be an effective alternative biocontrol agent to control melon thrips. In this study, the virulence of nine indigenous EPFs isolates was tested against the second instar larvae and adult melon thrips under laboratory conditions. The promising EPFs were selected and compared to commercial Beauveria bassiana A1 and imidacloprid on susceptible pepper plants infested with melon thrips under greenhouse conditions. The scanning electron microscope (SEM) observation was also performed. The results indicated that, out of the nine EPFs, B. bassiana-NCHU-157 (Bb-NCHU-157) caused the highest mortality in both larval (35%) and adult (98%) thrips at seven days post-inoculation, followed by Metarhizium lepidiotae-NCHU-9 (Ml-NCHU-9), which exhibited 31% larval and 81% adult mortality. Germ tube and appressorium formation were observed under the SEM after 36 h post-inoculation (hpi) for Ml-NCHU-9 and 48 hpi for Bb-NCHU-157 on adult melon thrips, respectively. While all biocontrol treatments were less effective than imidacloprid at suppressing thrips populations, both Bb-NCHU-157 and Ml-NCHU-9 were able to control the thrips population by up to 60% compared to the non-treated control under greenhouse conditions. However, there was no significant difference among Bb-NCHU-157, Ml-NCHU-9, and commercial biopesticide B. bassiana A1 treatments, highlighting the potential of these two indigenous isolates, Bb-NCHU-157 and Ml-NCHU-9, as viable biocontrol agents for melon thrips management.