Entomopathogenic nematodes (EPNs) of the genus Steinernema are pathogenic to the insects and well known as ideal models for understanding parasite-host interaction. EPNs harbor a number of bacterial symbionts in their gut belonging to the noble genus Xenorhabdus which are capable of killing insects by themselves or by combination with nematodes by suppressing insect immune defense. Here, we report host range of Steinernema monticolum and its symbiont Xenorhabdus hominickii. S. monticolum has a diverse host range including lepidopteran and coleopteran insects although they showed higher pathogenicity to the lepidopteran insects. Especially, X. hominickii suppressed insect immune responses. A target insect, Spodoptera exigua, exhibited both cellular and humoral immune responses by expressing antimicrobial peptides and forming nodules in response to heat-killed X. hominickii. However, live bacteria significantly suppressed the immune responses. An addition of arachidonic acid to the bacterial infection significantly rescued the immune responses, suggesting eicosanoid biosynthetic pathway as a pathogenic target of X. hominickii.

• Md. Sadekuzzaman(Department of Bioresource Sciences, Andong National University)
• Youngjin Park(Department of Bioresource Sciences, Andong National University)
• Yonggyun Kim(Department of Bioresource Sciences, Andong National University)