Potential of entomopathogenic fungus Isaria javanica for controlling the potato tuberworm Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae)

The potato tuberworm Phthorimaea operculella is an important cosmopolitan quarantine pest of the Solanaceae crops. Comparing the relative virulence of five entomopathogenic fungi against P. operculella, the results showed that Isaria javanica was more effective against eggs, larvae and pupae compared to the other tested isolates. Mean infection rates of ca 80 % were obtained for individuals at different life stages treated with 1×10⁸ conidia/mL. Based on the linear regression analyses of the mortality data, a median lethal concentration <1×10⁶ conidia/mL was calculated for eggs, larvae and pupae, suggesting that this isolate of I. javanica may be a useful biocontrol agent for P. operculella. Variation was observed in the growth rates and sporulation of I. javanica on different culture media and at different temperatures. When cultured on peptone maltose agar, the fungus grew quickly, but sporulation rates were higher on corn meal agar and potato dextrose agar, producing 8.16×10³ and 7.39×10³ conidia/cm², respectively. When cultured at different temperatures, the fungus grew faster at 27 °C, and produced more conidia when grown at temperatures under 30 °C. Our results indicate that I. javanica is a promising biocontrol agent for the potato tuberworm.