Industrial attractiveness of entomopathogenic Fusarium as biopesticide against melon thrips, Thrips palmi

Melon thrips, Thrips palmi (Thysanoptera: Thripidae), is a serious insect pest in crop productions, and synthetic chemicals are frequently used to control them. However, this practice causes residual issue in nature and makes melon thrips acquire strong resistance. To overcome these problems, a group of entomopathogenic fungi could be used as an alternative for controlling melon thrips. In this work, a total of 100 fungal isolates from soil in four different regions of Korea were isolated and subjected to virulence assays against melon thrips. Twenty-five highly virulent fungal isolates, which showed 100% mortality 6 days after treatment, were determined. Liquid-cultured filtrates of the selected isolates were further used to investigate their insecticidal activity against melon thrips, and of the 25 selected isolates finally seven isolates including Metarhizium spp. and Fusarium spp. showed high insecticidal activity in a dose-dependent manner. Under a thermal stress at 121°C, culture filtrates of the seven isolates still kept their insecticidal activities. When liquid-cultured spores were exposed to 45°C, spores of Fusarium isolates were resistant to the thermal stress, but those of Metarhizium isolates were susceptible to the stress. The culture filtrates of Fusarium isolates did not show any phytotoxicity to the tomato plants, followed by no phytotoxicity of liquid-cultured spores, although mycotoxins need to be further clearly characterized. This work suggests that entomopathogenic Fusarium isolates are competitive in virulence against melon thrips and production of insecticidal metabolites compared to Metarhizium, and particularly attractive in sporal resistance against thermal stress, significantly stronger than Metarhizium.