Heat tolerances, desiccation tolerances, and effectiveness of 10 Heterorhabditis bacteriophora strains isolated from different climatic regions in Turkey were analyzed in laboratory conditions. All strains were exposed to heat and desiccation conditions to determine their tolerance levels, and different doses of the strains were applied to the host larva to detect infection capabilities. Correlations between heat and desiccation tolerances as well as effectiveness of all strains were investigated. Moreover, relationships between the tolerances and geographic origins were examined. The results showed that there was no correlation between desiccation tolerance and effectiveness as well as between heat and desiccation tolerances. However, a significant correlation was found between heat tolerance and effectiveness. Furthermore, there was a correlation between heat tolerances and origins, but no correlation existed between desiccation tolerances and origins.