The potential and biochemical effects of the Steinernema carpocapsae, an entomopathogenic nematode, against two species of fruit flies in two types of soil texture (sand and sandy-loam) were examined under laboratory conditions. Data obtained revealed that the type of soil altered the potential effect of S. carpocapsae on Bactrocera zonata and Ceratitis capitata. The mortality percentages for B. zonata ranged between 30.00 and 94.43% in sand and between 33.33 and 96.67% in sandy-loam, whereas, for C. capitata, it ranged from 54.43 to 90.00% in sand and from 55.57 to 97.67% in sandy-loam. Generally, the mortality increased with the increase of nematode concentrations. According to LC₅₀ values, S. carpocapsae was more efficient against B. zonata in sand, but the opposite was obtained in sandy-loam against C. capitata. In addition, S. carpocapsae caused variable biochemical changes in activity of certain enzymes of the two fruit fly species, since it exhibited only a significant increase in the acid phosphatase in B. zonata, whereas the other tested enzymes significantly declined. The activity of amylase and acid phosphatase enzymes significantly induced in C. capitata, whereas the activity of trehalase, acetylcholine esterase and alkaline phosphatase significantly decreased. Non-significant effects were obtained in activity of invertase and chitinase within the infected individuals of C. capitata. Thus, the entomopathogenic nematodes could be used as a sustainable bio-control agent in Integrated Pest Management (IPM) programs for soil-inhabitant insects, such as fruit flies.