PATHOGENICITY OF AXENIC STEINERNEMA-FELTIAE, XENORHABDUS-BOVIENII, AND THE BACTO-HELMINTHIC COMPLEX TO LARVAE OF TIPULA-OLERACEA (DIPTERA) AND GALLERIA-MELLONELLA (LEPIDOPTERA)

The pathogenicity of the nematode-bacterium complex Steinernema feltia e-Xenorhabdus bovienii to larvae of Tipula oleracea and Galleria mello nella was investigated by injection of dauer juvenile nematodes carryi ng their bacterial symbiont cells (monoxenic nematodes). Axenic nemato des (free of bacteria) and the symbiotic bacteria themselves were test ed. The LC50 Of X. bovienii in T. oleracea was 15,700 colony forming u nits (CFU)/larva compared to less than or equal to 8 CFU in G. mellone lla. Xenorhabdus bovienii is apparently removed from the tipulids hemo lymph, possibly by cellular defense mechanisms. Axenic nematodes were less pathogenic than monoxenic nematodes for both insects. The differe nce was less pronounced in G. mellonella larvae: one axenic nematode w as sufficient to kill 80% in 1 day. The remaining insects found dead a fter 50 days were developmentally arrested In T. oleracea 20 axenic ne matodes caused 39% whereas 20 monoxenic dauer juveniles caused 90% mor tality within 8 days. The data indicate that the virulence of the S. f eltiae/X. bovienii complex is greater than the additive effect of the nematodes and their bacteria, further evidence for the synergistic act ivity of the symbiotic bacto-helminthic complex during pathogenesis. ( C) 1997 Academic Press.