Heterorhabditis is frequently found in coastal sandy soils where it may experience both high salinity and high temperatures. We tested the ability of infective juveniles (IJs) of three taxonomic groups of Heterorhabditis to infect insects in saline sand. We also tested whether salinity (sea water) affected the IJs' ability to tolerate elevated temperatures in aqueous suspension and in sand. IJs of all three taxonomic groups killed Galleria mellonella in saline sand (25.6% insects killed), but at a lower level than in non-saline sand (96.5% insects killed). Exposure of IJs in sand to high temperature reduced their ability to kill G. mellonella at 20 degrees C; heating IJs in saline sand reduced G. mellonella mortality to a lesser extent (25.6% at 20 degrees C, 18.3% at 39 degrees C) than heating in non-saline sand (96.5% at 20 degrees C, 17.5% at 39 degrees C). In aqueous suspension, IJs of the North-West European and Irish types of Heterorhabditis tolerated high temperature better in sea water (at least 95% survived 1 h at 39 C) than in distilled water (none survived 1 h at 38 degrees C). H. bacteriophora was more temperature tolerant: survival and subsequent infectivity of IJs was unaffected by temperature up to 39 degrees C in either medium. It was concluded that high salinity (sea water) reduces the ability of Heterorhabditis IJs to infect, but improves their tolerance of high temperature.