The entomogenous nematodesSteinernema feltiaeFilipjev (=Neoaplectana carpocapsaeWeiser) andHeterorhabditis heliothidis(Khan, Brooks&Hirschmann) were encapsulated in calcium alginate and fed to larvae ofSpodoptera exigua(Hübner) in petri dishes. While feeding on the capsules, the larvae released the nematodes. When moisture was present, larval mortality was nearly 100%, but little or no mortality occurred when free moisture was not present.S. feltiaein the capsules survived for 8 months with no detectable loss in survivability or infectivity when stored at 4°C. Capsules coated with a lipid membrane were completely desiccated at 50% RH with no nematode survivors, but at 72% RH, 71.2% of the nematodes were alive after 24 h. Potential use of the capsules containing these nematodes for insect control is discussed.