INVOLVEMENT OF LARVICIDAL TOXINS IN PATHOGENESIS OF INSECT PARASITISM WITH THE RHABDITOID NEMATODES, STEINERNEMA-FELTIAE AND HETERORHABDITIS-BACTERIOPHORA

The insect-parasitic rhabditoid nematodes, Steinenema feltiae and Heterorhabditis bacteriophora, released a compound/s/ toxic to larvae of the greater wax moth, Galleria mellonella, that caused paralysis and death of the insect. Larvicidal substances appeared in wax moth larvae during parasitism and after inoculation with the primary form of the bacterial associates of the nematodes. The nematode S. feltiae and its associate, Xenorhabdus nematophilus, excreted much less toxic activity within larval body than H. bacteriophora. The secondary form of Xenorhabdus did not produce toxin in parasitized larvae, but X. luminescens, the bacterium associated with H. bacteriophora, released detectable titer of toxin activity in broth cultures. Both nematode toxins were sensitive to heat and produced a specific type of proteolytic activity. Preliminary identification of the compounds responsible for larval toxicity revealed similarities to immune inhibitors produced by some bacterial pathogens of insects.