ISOLATION AND ENUMERATION OF SERRATIA-ENTOMOPHILA - A BACTERIAL PATHOGEN OF THE NEW-ZEALAND GRASS GRUB, COSTELYTRA-ZEALANDICA

Several agar media were tested for their use in a selective isolation and identification scheme for Serratia entomophila, a bacterium causin g amber disease of the New Zealand grass grub, Costelytra zealandica ( White). Soil dilutions were plated on caprylate thallous agar (CTA), s elective for Serratia spp. Most strains of Ser. entomophila grew well on CTA; the mean efficiency of colony formation on CTA was 94 +/- 3% o f that on a non-selective medium. The identity of colonies growing on CTA was determined on the basis of their growth reactions on DNase-tol uidine blue agar, adonitol agar and itaconate agar. Serratia entomophi la could be distinguished from other Serratia spp. found in New Zealan d soils, in particular Ser. proteamaculans, another causal agent of am ber disease of grass grub. The identification scheme allowed the selec tive recovery of Ser. entomophila from field soils containing a divers e microflora.