The influence of phase variants of Xenorhabdus spp. and Escherichia coli (Enterobacteriaceae) on the propagation of entomopathogenic nematodes of the genera Steinernema and Heterorhabditis

Abstract

Institutfiir Phytopathologie, Christian-Albrechts-Universitiit, Hermann-Rodewald-Strasse 9,2300 Kiel, Federal Republic of Germany. SUMMARY To quantify the assumed negative influence of phase II Xenorhabdus spp. on the propagation of entomopathogenic Steinemema and Heterorhabditis nematodes, the in vitro and in vivo reproduction potentials of five nematode species (strains) were determined. Bacteria-free S. carpocapsae (DD-136) were fed with phase variants (primary and secondary form) of X. nematophilus and with Escherichia Coli. The growth profiles, determined by counting nematodes in three day intervals from cultures started with one female nematode, showed no significant differences between the reproduction potentials on phase 1 or II or E. Coli cultures. Growth on E. coli resulted, however, in a delay of nematode development by about 6 days. Phase variants of X. bovienii and X. poinarii did not signifcantly alter the number of off-Springs per female, final nematode yields, the generation time or the body Iength of the females of S. bibionis (OBS III) and Steinemema sp. (NC 513), respectively. The same results were obtained with H. heliothidis (NC-1 [HH]) and Heterorhabditis sp. (NZ). Phase II variants caused, however, a higher nematode mortality than phase 1 ’ X. luminbscens. The phase 1 bacterium of strain NZ stayed stable for 6 months. A stable phase II could only be obtained after prolonged subculturing for 11 months and resulted in an orange and a yellow pigmented clone. Nematode development was totally inhibited on the yellow pigmented variant. Percent mortality of last instar Galleria mellonella larvae did not differ when axenic or phase 1 or II bearing S. carpocapsae and Steinemenza sp. (NC 513) dauer larvae were used. The propagation of phase II symbiont carrying nematodes was always lower. The reasons for the different nematode yields obtained from in vitro and in vivo cultures are discussed.