Characterisation of mosquito larvicidal compounds from cultures of a basidiomycete coriolus hirsutus

Abstract

Mosquitoes transmit serious human diseases, resulting into millions of deaths globally every year. The use of synthetic insecticides to control vector mosquitoes has caused physiological resistance and adverse environmental effects in addition to high operational costs. Mosquito larvicidal compounds from certain plant and fungal species have been reported. Basidiomycetes fungi are known to synthesize a wide range of bioactive secondary metabolites. The objective of this work was to investigate the mosquito larvicidal compound(s) from the fungus Coriolus hirsutus belonging to the basidiomycete class of fungi. Crude extracts prepared from fermented liquid nutrient media cultures of Coriolus hirsutus were found to exhibit activity against the larvae of Aedes aegypti species of mosquito. The active crude extracts were further subjected to bioactivity guided fractionation that led to the purification of two larvicidal compounds. Chemical investigation using NMR spectroscopy and MS experiments identified the two compounds, 17–(5–hydroxy–1,5-dimethyl-hex-3-enyl)-4,4,8,10,13-pentamethyl 4,5,6,7,8,9,10,11,12,13,14,15,16,17- tetradecahydro-3H-cyclopenta[α]phenanthren-3-ol and hexanoic acid. 17–(5–hydroxy–1,5-dimethyl-hex-3-enyl)-4,4,8,10,13-pentamethyl-4,5,6,7,8,9,10,11,12,13,14,15,16,17-tetradecahydro-3H-cyclopenta[α]phenanthren-3-ol had an LC50 and LC90 of 147.0 ppm and 285.3 ppm at 95%CI while hexanoic acid had an LC50 and LC90 of 237.8 ppm and 393.9 ppm at 95%CI. The two larvicidal compounds obtained from Coriolus hirsutus may constitute important alternatives to the synthetic insecticides under the integrated vector control strategies.