Temperature effects on Korean entomopathogenic nematodes, Steinernema glaseri and S. longicaudum, and their symbiotic bacteria

We investigated the temperature effects on the virulence, development, reproduction, and motility of two Korean isolates of entomopathogenic nematodes, Steinernema glaseri Dongrae strain and S. longicaudum Nonsan strain. In addition, We studied the growth and virulence of their respective symbiotic bacterium, Xenorhabdus poinarii for S. glaseri and Xenorhabdus sp. for S. longicaudum, in an insect host at different temperatures. Insects infected with the nematode-bacterium complex or the symbiotic bacterium was placed at 13°C, 18°C, 24°C, 30°C, or 35°C in the dark and the various parameters were monitored. Both nematode species caused mortality at all temperatures tested, with higher mortalities occurring at temperatures between 24°C and 30°C. However, S. longicaudum was better adapted to cold temperatures and caused higher mortality at 18°C than S. glaseri. Both nematode species developed to adult at all temperatures, but no progeny production occurred at 13°C or 35°C. For S. glaseri, nematode progeny production was best at inocula levels above 20 infective juveniles/host at 24°C and 30°C, but for S. longicaudum, progeny production was generally better at 24°C. Steinernema glaseri showed the greatest motility at 30°C, whereas S. longicaudum showed good motility at 24°C and 30°C. Both bacterial species grew at all tested temperatures, but Xenorhabdus sp. was more virulent at low temperatures (13°C and 18°C) than X. poinarii.