The susceptibility of soil associated late instar pink bollworm (PBW), Pectinophora gossypiella (Saunders), larvae to two species of Steinernema in spring and summer was evaluated in small scale field tests in 1993. Steinernema carpocapsae (Weiser), used in previous tests, was selected as a standard and S. riobravis, Poinar, Raulston, Cabanillas, a more high temperature-tolerant nematode with greater host searching capability, was selected as the most efficacious for summer applications. For the spring test, PBW mortality response, at 15 infective juveniles/cm2 for S. carpocapsae and S. riobravis was not significantly different at 87 and 89%, respectively. The midsummer tests resulted in a significant difference in PBW comparative mortality of S. carpocapsae and S. riobravis at the four concentrations tested. A simple method was developed for small scale field testing and efficacy monitoring for PBW and other soil associated insects. The results suggest that the high temperature-tolerant entomopathogenic nematode, S. riobravis, will be more effective than S. carpocapsae in summer applications. Five separate small scale field evaluations (1991-1993) indicate pink bollworm populations can be effectively reduced by the application of these mobile, host searching, EPA exempt, and commercially available biorational control agents.