Development of Mucor hiemalis wettable powder and its biological activity against Evergestis extimalis Scopoli

To further enhance the biological activity of Mucor hiemalis against Evergestis extimalis Scopoli, single-factor experiments and orthogonal array designs were used to identify the carriers and additives with minimal impact on the viability of M. hiemalis QH01. An optimized formulation of M. hiemalis wettable powder (WP) was established. The results showed that the optimum formulation of the WP consisted of 1 × 10⁸ spores / mL, 30 % white carbon black (carrier), 4 % sodium carboxymethyl cellulose (CMC-Na, dispersant), 2 % polyethylene glycol 6000 (PEG6000, wetting agent), and 1 % ascorbic acid (V_C, ultraviolet protectant). The WP exhibited a suspension of 85.03 %, a wetting time of 56 s, a pH value of 7.05, a fineness of 97.52 %, and a water content of 2.33 %. Stability test revealed no significant change in the viable count of the WP at the temperature ranging of 20 to 40 ℃ (P > 0.05). After 120 minutes of ultraviolet radiation, it still retains a certain level of activity (spore concentration of 0.28 × 10⁸ spores/mL). When the pH value is between 6 and 8, there is no significant change in the viable bacteria count (P > 0.05) and the spore concentration can reach 1 × 10⁸ spores/mL. After 45 days of indoor storage, the spore concentration decreased slightly but remained at 0.77 × 10⁸ spores/mL, indicating good stability. The results of indoor bioassay showed that after 5 days of treatment with 1.0 × 10⁸ spores/mL of the WP of Mucor hiemalis, the median lethal time (LT₅₀) value for the 3rd instar larvae of Evergestis extimalis Scopoli was the lowest, at 2.1 days, highlighting its promising potential for practical application.