The kinetic properties of two metabolic enzymes, glucose-6-phosphate dehydrogenase and hexokinase, were studied in four strains of entomopathogenic nematodes that had been recycled for two years at various temperatures: Steinernema feltiae NF strain, Steinernema feltiae Umeå strain, Steinernema carpocapsae All strain, Steinernema riobravis TX strain. The recycling temperatures influenced the activities of glucose-6-phosphate dehydrogenase and hexokinase in an adaptive fashion in all the strains. At each assay temperature (5-35 degrees C), the maximum specific activity of both the enzymes was greater in the nematodes that had been recycled at lower temperatures than in those reared at higher temperatures. In three enzyme-nematode strain combinations, the lowest K(m) values measured at each assay temperature occurred in nematodes that had been recycled at the lower temperatures. However, the assay temperatures at which the minimum K(m) values occurred were > or = 15 degrees C. The capacities of these nematodes to adjust to different recycling temperatures is discussed in relation to the physiological mechanisms involved.