Using the secondary metabolites of some fungi and wild plants as natural pesticides to control cotton mealybug, Phenacoccus solenopsis (Hemiptera: Pseudococcidae)

Abstract

As alternatives to chemical insecticides, entomopathogenic fungi or wild plants and their secondary metabolites are being used. These biocontrol agents are significant because of their biodegradability, specificity, eco-friendliness, and utility as agents to reduce insecticide resistance. In this study five ethyl acetate extracts of locally isolated fungal strains (Ta laromyces atroroseus, Fusarium chlamydosporum, Talaromyces stipitatus, Trichoderma lixii, Beauveria bassiana) as well as alkaloid extract of Haloxylon salicornicum were extracted and investigated as biocontrol agents against cotton mealybug Phenacoccus solenopsis. The results indicated that all extracts had toxic effects against P. solenopsis except the extract of T. stipitatus. The LC 50 values and toxicity index indicated that the alkaloid extract of H. salicornicum was the most toxic one (26 ppm) after 72 hours of treatment followed by the extracts of F. chlamydosporum (77 ppm), then B. bassiana (84 ppm) and T. lixii (118 ppm). On the other hand, there were significant changes in tested insect enzyme activities (amylase, lipase, glutamic oxaloacetic transaminase (GOT), glutamic pyruvic transaminase (GPT), and acetyl choline esterase (AchE) as well as total proteins and lipids in the insects treated with the alkaloid extract of H. salicornicum, and ethyl acetate extracts of F. chlamydosporum and B. bassiana after 24 hours of treatment compared to the control. GC/MS analyses of fungal extracts indicated that there were some bioactive compounds like hexadecanoic acid, octadecanoic acid, and tetradecanoic acid. In addition, the anabasine compound was found as a major constituent of the alkaloid extract of H. salicornicum and identified by 1H NMR and GC/MS analysis. In conclusion, according to this study, it was recommended that the alkaloid extract of H. salicornicum and the ethyl acetate extracts of F. chlamydosporum, B. bassiana, and T. lixii be used as alternatives to chemical insecticides for controlling the cotton mealybug P. solenopsis.