Induction of immune response among formosan subterranean termites, Coptotermes formosanus Shiraki (Rhinotermitidae: Isoptera)

Abstract

The antimicrobial activity from the whole body homogenates of immunized workers of Coptotermes formosanus Shiraki with entomopathogenic fungi (Metarhizium anisopliae, strain 2049 and strain 406; Beauveria bassiana, strain 3005 and 200436) and bacteria (Bacillus thuringiensis, Escherichia coli, Ralstonia solanacearum and Staphylococcus aureus), were checked by inhibition zone assay against B. thuringiensis, E. coli, R. solanacearum and S. aureus bacteria. Among all the successful inducers, two peaks at different times were observed, suggesting that there might be different antimicrobial peptides. Furthermore, the results showed that entomopathogenic fungi greatly induced the antimicrobial response of the homogenates as compared to bacteria. The pattern of antimicrobial response varied with the time of treatment, and with the strain of micro-organism. For the time course, after 4 to 8 h of infection, the homogenates started showing antimicrobial activity. Homogenates infected with M. anisopliae strain (2049) showed the highest activity against B. thuringiensis after 18 h post inoculation. While, B. bassiana strain (3005) showed the highest activity against B. thuringiensis after 12 h postinoculation. The antibacterial activity was only observed from the homogenates prepared between 4-80 h post-inoculation. Furthermore, for the different microbial strain, a Gram-negative bacterium, E. coli was found to be highly resistant, showing no growth inhibition. While, both the studied Gram-positive bacteria found to be susceptible to the homogenates, resulting very high antibacterial activity. Among all the microbes, R. solanacearum and S. aureus were found to be poor inducer of immune system in the studied insect. The results provide the first evidence of the induction of antimicrobial response in C. formosanus workers. The current findings open new avenues for further exploration of molecular mechanism of immune response in termites.