Abstract

Entomopathogenic fungi (EPF) are highly effective in infecting insects and are commonly used for insect pest control due to their environmental safety and bio-persistence. This study focused on selecting effective EPF isolates obtained from Nakhon Ratchasima province for controlling mealybugs and investigating their relationship with protease and lipase activity. During this study EPF isolates were collected from soil samples in Nakhon Ratchasima province using the baiting technique with yellow mealworms (Tenebrio molitor L.). A total of 12 isolates of Metarhizium spp. were obtained. When cultured on potato dextrose agar (PDA) medium for 21 days, the NMMet_BAL7/1 isolate had the largest colony diameter (71.00 mm), but this was not statistically different (P > 0.05) from NMMet_NS4/1, NMMet_TPR10/2, and NMMet_SD9/1 isolates. The enzyme activity tests showed that all isolates exhibited both protease and lipase, with significant differences among them (P < 0.05). Protease activity ranged from 0.12 to 0.33, while lipase activity varied from 0.16 to 0.54. The NMMet_SS2/2 isolate showed the highest protease (0.33) and lipase (0.54). The ability of all 12 EPF isolates to control 3rd instar nymph mealybugs was tested in a laboratory environment by spraying the mealybugs with an EPF spore suspension at a concentration of 1x108 spores/mL. The NMMet_SS2/2 isolate resulted in the highest mortality and infection rate of mealybugs (96.67%), which was statistically different (P < 0.05) from other EPF isolates. NMMet_BAL7/1 showed the second highest mortality and infection rate (68.33%). This study suggests that enzyme activity is correlated with EPF virurence, underscoring NMMet_SS2/2 as a promising candidate for field testing.