Steinernema riobravis Cabanillas, Poinar and Raulston, after release on the soil surface in horizontally or vertically oriented bioassay chambers, moved greater distances (in cm) to infect pink bollworm (PBW), Pectinophora gossypiella (Saunders) larval hosts compared with S. carpocapsae (Weiser) (Kapow selection). Both nematode species induced greater PBW larval mortality in soil with a moisture level of 30% compared with 25% soil moisture.