Effect of propagation temperatures on temperature tolerances of entomopathogenic nematodes

Four isolates (= 3 species) of steinernematids were propagated at 25, 20 and when possible, 15 and 10 degrees C for 2 years, then their capacities for tolerating high temperatures and freezing determined. In all isolates, the temperature at which 50% of the infective juveniles died (LT50) increased with an increase in maintenance temperature. Steinernema riobravis [S. riobravae] had the highest LT50 values, S. feltiae strains the lowest, while S. carpocapsae A11 strain displayed an intermediate degree of tolerance to high temperatures. Tolerance to freezing, as measured by times at which 50% of the infective juveniles were killed by a -5 degrees C regime, was diminished at higher maintenance temperatures. The infectivity of nematodes that survived freezing was at least 90 that of unfrozen nematodes (controls). Two strains of S. feltiae were the most cold tolerant of the 4 isolates, but their capacities to withstand freezing were diminished by propagation at warmer temperatures..