Host-pathogen interactions are very complex processes. Like many entomopathogenic fungi during infection process, Beauveria bassiana, produces enzymes which are able to destroy insects cuticle in order to penetrating into the host. Chitinases are considered to be the important enzymes for the hydrolysis of chitin and play an important role in the biological control of various pests including onion thrips. In the present study, specific primers for CHit1 and CHit2 genes were designed to study expression pattern of these two chitinases from Beauveria bassiana IRAN 789C strain before and after interaction with the second instar larvae of Thrips tabaci. Larval inoculation was carried out using three conidial concentrations, 104, 105 and 106 conidia per ml. The results showed that, no genes were expressed in all conidial concentrations before parasitic interaction; both genes were expressed in all conidial concentrations, after parasitic interaction. Increasing conidial concentration of Beauveria bassiana caused upregulation of chitinases expression level. Expression of these genes during parasitic interaction of the fungus and the insect larvae reflects the importance of chitinases gene as an effective factor in biological control of target organisms.

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