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This is a bionomic study of the entomopathogenic nematodes (EPN) Heterorhabditis atacamensis and Steinernema unicornum, from the Atacama Desert and Tierra del Fuego in Chile, respectively. At 20 degrees C, H. atacamensis infective juveniles took 22 days to emerge from cadavers, S. unicornum took 24 days. The thermal infectivity range for H. atacamensis was wider than S. unicornum (10-35 degrees C vs 10-30 degrees C). Exposure to 37 degrees C for 60 min killed 100% H. atacamensis and 57% S. unicornum. Heterorhabditis atacamensis caused 53% insect mortality at the lower end of the soil moisture range, S. unicornum caused 100%; both caused >= 85% mortality at the upper end (near saturation point). Heterorhabditis atacamensis killed three of six insect species; however, mortality was relatively low for each (< 35%). Steinernema unicornum killed five of six species, with mortality consistently > 50%; mortality of the fruit tree weevil Naupactus xanthographus was highest (90%).