Axenic, third stage juveniles of the Mexican strain of Steinernema feltiae did not alter the total hemocyte counts of larval Galleria mellonella, whereas those of monoxenically cultured juveniles did. In the latter case, the hemocytes were vacuolated. The concentration of Xenorhabdus nematophilus subsp. nematophilus var. mexicanus increased 12-fold within 6 hr of injecting the bacteria into G. mellonella. The presence of the axenic Mexican strain of S. feltiae in G. mellonella hemocoel for up to 5 hr did not change the rate of removal of injected Bacillus subtilis or X. nematophilus subsp. nematophilus var. mexicanus from the hemolymph. Xenorhabdus nematophilus subsp. nematophilus var. mexicanus was cultured in synthetic Galleria serum supplemented with larval serum in the presence and absence of S. feltiae. These spent media, once sterilized and injected into G. mellonella, did not influence insect behavior, silk production, insect mass or mortality.