ACTIVE RESISTANCE OF ENTOMOPHAGOUS RHABDITID HETERORHABDITIS-BACTERIOPHORA TO INSECT IMMUNITY

A specific extracellular proteinase, degrading selectively the cecropi n-based defence system of insects, is secreted into the larval body du ring parasitism of the greater wax moth by the Heterorhabditis bacteri ophora/Photorhabdus luminescens complex and by phase 1 of P. luminesce ns. The proteolytic digestion of insect inducible cecropin-like immune molecules was demonstrated by the disappearance of the Galleria mello nella cecropins and purified Hyalophora cecropin B peptide PAGE bands upon exposure to infected extracts, and a similar abrogation of antiba cterial activity using an agar diffusion assay. Proteolytic activity o f infected extracts produced by nematode/bacterial complex and phase 1 variant of P. luminescens was shown to be correlated with cecropin-in hibitory activity, suggesting that this anti-cecropin agent may be res ponsible for the ability of bacteria to establish infection and the in secticidal nature of H. bacteriophora. Antibacterial activity of Galle ria lysozyme and that of chicken egg-white lysozyme to which P. lumine scens is insensitive, was unaffected by H. bacteriophora proteinase.