Effect of salt and temperature stresses on survival and infectivity of Heterorhabditis spp. IJs

Heterorhabditis is frequently found in coastal sandy soils where it may exp erience both high salinity and high temperatures. We tested the ability of infective juveniles (IJs) of three taxonomic groups of Heterorhabditis to i nfect insects in saline sand. We also tested whether salinity (sea water) a ffected the IJs' ability to tolerate elevated temperatures in aqueous suspe nsion and in sand. Us of all three taxonomic groups killed Galleria mellone lla in saline sand (25.6% insects killed), but at a lower level than in non -saline sand (96.5% insects killed). Exposure of Us in sand to high tempera ture reduced their ability to kill G. mellonella at 20 degrees C; heating U s 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, Us of t he North-West European and Irish types of Heterorhabditis tolerated high te mperature better in sea water (at least 95% survived 1 h at 39 degrees C) t han in distilled water (none survived 1 h at 38 degrees C). H. bacteriophor a 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 Heterorhabd itis IJs to infect, but improves their tolerance of high temperature.