In a laboratory experiment an efficacy of entomopathogenic nematode Steinernema feltiae in controlling third-stage larvae of common cockchafer (Melolontha melolontha) was studied. The experiment comprised of commercial product Entonem and indigenous strain C76. The efficacy of both biological agents was tested at 20 and 25 °C and at four different concentrations of nematode suspension: 0, 250.000 infective juveniles IJs/m2, 500.000 IJs/m2, and 1.000.000 IJs/m2. Higher mortality rate (27 %) of white grubs was obtained for strain C76 rather than for commercial product (20 %). In our experiment temperature proved to be the most limiting factor in efficacy of tested biological agents. Meanwhile, mortality rate at 20 °C was 34 % and only 12 % mortality was achieved at 25 °C. At highest concentration of nematode suspension and 20 °C also the highest mortality rate (53 %) with strain C76 was obtained. V laboratorijskem poskusu smo preučevali učinkovitost entomopatogene ogorčice Steinernema feltiae za zatiranje ličink tretje larvalne stopnje poljskega majskega hrošča (Melolontha melolontha). V poskus smo vključili komercialni pripravek Entonem in domorodno raso C76. Delovanje omenjenih biotičnih agensov smo ugotavljali pri 20 in 25 °C ter štirih različnih koncentracijah suspenzije ogorčic: 0, 250.000 infektivnih ličink IL/m2, 500.000 IL/m2 in 1.000.000 IL/m2. Rasa C76 je vplivala na višjo stopnjo smrtnosti (27 %) ogrcev, v primerjavi s komercialnim pripravkom (20 %). Temperatura se je v našem poskusu izkazala kot najbolj omejujoč dejavnik učinkovitosti preizkušanih biotičnih agensov, saj smo pri 20 °C dosegli 34 % smrtnost ogrcev, medtem ko je bila ta pri 25 °C le 12 %. Pri najvišji koncentraciji suspenzije ogorčic in 20 °C je bila pri rasi C76 dosežena najvišja stopnja smrtnosti ogrcev, in sicer 53 %.