Abstract: 【Aim】 The rapid evolution of resistance of Tetranychus truncatus to pesticides has made it increasingly difficult to control. Consequently, it is urgent to develop microbial acaricides. The entomopathogenic fungus Cordyceps javanica JS001 strain has been developed as a biocontrol agent against pests such as Bemisi tabaci. The aim of this study is to explore the pathogenicity of C. javanica to T. truncatus and its ideal adjuvant materials, so as to reveal the biocontrol potential of C. javanica on T. truncatus. 【Methods】 We determined the cumulative mortality rates of eggs, nymphs and adults of T. truncatus after spraying the spore suspension (1.0×10⁶ spores/mL) of C. javanica JS001 strain. By spraying diatomaceous earth (0.025 g/L) solution and spore suspension of C. javanica JS001 strain (1.0×10⁶ spores/mL) combined with diatomaceous earth to the 2-day-old adults of T. truncatus, we observed and recorded the infection status and death of the adult T. truncates. After spraying diatomaceous earth (0.025 g/L) solution, we observed and calculated the distance between cuticle wrinkles and the number of wrinkles within unit distance (10 μm) of the 2-day-old adults of T. truncatus using scanning electron microscopy. 【Results】 C. javanica JS001 strain showed no pathogenicity to T. truncatus eggs. The mortality rate of adult T. truncatus caused by C. javanica JS001 strain was 81.75%, which was significantly higher than the mortality rate of nymphs (40.91%). Moreover, diatomaceous earth could accelerate the lethal effect of C. javanica JS001 strain on adult T. truncatus, shortening the average survival time by 0.6 d. Results of scanning electron microscopy observation showed that, compared with the control, diatomaceous earth treatment loosened the microarray structure of T. truncatus adult cuticles, significantly increased the average distance between adjacent wrinkles, and significantly decreased the average number of wrinkles within unit distance (10 μm). 【Conclusion】 C. javanica JS001 strain has a high pathogenicity against T. truncatus adults. Diatomaceous earth can alter the physical structure of the T. truncatus adult cuticle and enhance the acaricidal activity of C. javanica JS001 strain.

Key words: Tetranychus truncatus, Cordyceps javanica, pathogenicity, diatomaceous earth, cuticle, biological control