Bioscouring of mealybug wax using fungal enzymes for sustainable management of mealybugs in mulberry

Mealybugs (Hemiptera: Pseudococcidae) are small, soft-bodied plant sap-sucking insects. They constitute the second largest family of scale insects (Hemiptera: Coccoidea), with more than 2,000 described species and ca. 290 genera and 158 species. In mulberry, the pink mealy bug (Maconellicoccus hirsutus) creates recurring damage during pre-monsoon and post-monsoon in both irrigated and rainfed conditions. The formation of crinkling and dark green brittle leaves at the apical portions of the shoot is commonly referred to as “Tukra disease”. The pesticidal use for the control of Tukra is highly restricted in mulberry due to the residual susceptibility of silkworms. Although biological control seems viable and cost-effective, the unforeseen effects of bioagents on silkworms restrict their utility in sericulture. Therefore, alternative and sustainable methods are highly preferred. In the current investigation, enzymes were isolated from the four fungal isolates, namely Aspergillus fumigatus, Aspergillus terreus, and Aspergillus glaucus. The fungal enzyme extracts were separated into different time fractions (Fractions 1 to 5) using column chromatography (silica gel G-60). The enzyme fractions were sprayed once on eggs, 1st, 2nd, 3rd instars, and on adults of mealybug. Eggs and 1st instar larvae exhibited complete mortality within 24 h of treatment, while the 2nd instar larvae demonstrated the greatest vulnerability, with a mortality rate of 68.9% following exposure to the Aspergillus fumigatus SF-22 enzyme extract. Notably, the wax degradation by the microbial enzymes occurs within a short period of 7 days. The A. fumigatus SF-12 had shown higher larval weight as compared to the control in the 3rd instar. The A. fumigatus SF-13 showed the lowest larval and wax weight. The enzymes from A. fumigatus were found to be promising in the reduction of wax and larval weight. These interesting results pave the path to the sustainable management of mealybugs using fungal enzymes.