On the enzymes’ actions of entomopathogenic fungi against certain indigenous and invasive insect pests

摘要

Pathogenicity of entomopathogenic fungi (EPF) depends mainly on their ability to produce efficient enzymes, which degrade insect’s integument and other cellular components. Lipases are the first enzymes secreted by these fungi, then proteases, phospholipases, and chitinases. Twenty-six fungal strains, isolated from the aphids, Aphis sp., Linnaeus (Homoptera, Aphididae), the tomato leaf minor, Liriomyza trifolii, Burgess (Diptera, Agromyzidae) (indigenous insects), the red palm weevil, Rhynchophorus ferrugineus, Olivier (Coleoptera, Curculionidae), and the peach fruit fly, Bactrocera zonata, Saunders (Diptera, Tephritidae) (invasive insects) were tested for their enzymatic activities. Results showed that the majority of these strains were able to produce lipolytic enzymes with the most active being Aspergillus niger, Botryotrichum atrogriseum, Cochliobolus spicifer, Fusarium chlamydosporum, and F. proliferatum. Phospholipase was successfully produced by 73.1% of the tested strains among which Aspergillus flavus, A. niger, Mucor racemosus, Pochonia chlamydosporia var. catenulata, and Scopulariopsis brevicaulis were the highest producers. Proteolytic enzymes were detected in cultures of all the fungal strains except Aspergillus chevalieri and M. racemosus. The best proteolytic strain was S. brevicaulis followed by A. flavus, A. sydowii, and F. semitectum. The chitinolytic ability of the fungal strains was generally weak and the relatively active species belonged to A. flavus, A. niger, B. atrogriseum, F. chlamydosporum, F. solani, S. brevicaulis, and Nigrospora oryzae. Quantitative determination of chitinase revealed that the enzyme concentration ranged from 3.478 to 6.44 IU/ml. Most of the isolated fungi had enzymatic activities, but A. niger, F. semitectum, F. solani, F. chlamydosporum, P. chlamydosporia var. catenulata, and S. brevicaulis, were the most active ones.