Immune defense of Pieris brassicae larvae in challenged with Heterorhabditis bacteriophora, its symbiotic bacteria and metabolites

Abstract

In this study, virulence of the culture broth of Photorhabdus temperata subsp. temperata and its aqueous and organic extracts were investigated for 3rd and 4th instars of Pieris brassicae (Lepidoptera: Pieridae) larvae. Virulent efficacy was found in all the treatments. However, the culture broth of bacteria showed greater mortality effect. Also, this study presents the response of P. brassicae immune system factors, phenoloxidase, lysozyme and hemocytes, to infection by Heterorhabditis bacteriophora, its symbiotic bacteria and their aqueous and organic extracts. Results showed that after injecting infective juveniles (IJs) with phenoloxidase, specific activity was suppressed after primary increase. However, the phenoloxidase specific activity suppression was observed earlier after injecting P. temperata subsp. temperata, aqueous and organic extracts. Also, results indicate more phenoloxidase activity of 4th instars larvae in comparison with 3rd instars larvae, which can show higher activity of phenoloxidase in the 4th larval stage. After injecting IJs into hemocel, the total hemocyte count was increased until five h post-injection and then decreased at seven hours post-injection. Differential Hemocyte Count (DHC) indicated granolucytes and plasmocytes as frequent hemocytes after treatment. Lysozyme consideration showed an increase after injecting living and heat-killed bacteria into hemocel.