Technical Abstract: The entomopathogenic nematode Steinernema carpocapsae has shown promise for control of adult stage pecan weevil, Curculio caryae, a key pest of pecan. Our objective was to determine the feasibility of developing improved strains of S. carpocapsae by transferring the nematode’s bacterial symbiont (Xenorhabdus nematophila) from the Italian strain (which is highly virulent but has poor environmental tolerance) to the less virulent but more environmentally tolerant DD-136 strain, and through hybridization between the two wild type nematodes. Three modified strains were created: one through bacterial transfer alone and two hybrids through controlled crosses. We hypothesized that the improvement approaches would result in strains possessing high levels of heat and desiccation tolerance similar to DD-136 and virulence similar to the Italian strain. The hypothesis was supported in two out of three modified strains. Overall, the results indicate that bacterial transfer and hybridization could be a valuable tool in improving biocontrol efficacy of steinernematids.