LAUSR

This study describes the mortality effects of the culture broth of Xenorhabdus bovienii and its aqueous and organic extracts on Pieris brassicae larvae. All the treatments had insecticidal activities when injected into the haemocoel. The culture broth of bacteria and its aqueous extracts exhibited more insecticidal activity. The results showed the immune response of P. brassicae exposed to Steinernema feltiae , its symbiont bacteria, X. bovienii , and aqueous and organic extracts of bacteria. Both cellular and humoral responses were investigated. After infection of the larvae of P. brassicae with S. feltiae , the total number of haemocytes quickly increased. A reduction in the number of haemocytes was observed over post-injection time. In addition, plasmatocytes and granulocytes showed increased frequency and significant changes when compared to other haemocytes in responding to entomopathogenic nematode injection. Steinernema feltiae increased phenoloxidase activity but 3 h post-injection the concentration gradually decreased. However, a reduction in phenoloxidase activity was observed when the larvae were infected with bacteria or their aqueous and organic extracts. This study showed that both living and heat-killed bacteria have suppression effects on phenoloxidase activity. The lysozyme concentration increased in P. brassicae larvae when they were exposed to living and heat-killed X. bovienii . No suppression effect of the bacteria was detected on lysozyme.