Selection, development and testing of phage‐resistant strains ofSerratia entomophilafor grass grub control

Abstract

Use of the bacterium Serratia entomophila as an inundative biological control agent for the New Zealand grass grub (Costelytra zealandica) depends on the consistent production of high yields of the bacterium in liquid fermentation. Following the phage related failure of several S. entomophila fermentations, a programme was initiated to isolate phage‐resistant strains. No naturally occurring strains were found to be resistant to eight stocks of phage isolated from either grass grub larvae or the fermenter. Therefore, ethylmethane sulphonate was used to generate phage‐resistant mutants. Strains which showed cross resistance to all eight phage test stocks were tested for pathogenicity towards grass grub. Several strains showing unimpaired pathogenicity were selected for further tests. Four of these phage‐resistant strains produced high cell yields, even when grown in the presence of high numbers of fermenter‐derived phage. Phage‐resistant strains have subsequently been produced in bulk in industrial fermente...