The biological activity of entomopathogenic nematodes (EPNs) against the larvae and adults of the economically important Oulema melanopus (L.) (Coleoptera: Chysomelidae) was assessed under laboratory conditions. The EPNs assessed were five native isolates of the species Steinernema feltiae (Filipjev) and Heterorhabditis megidis (Poinar, Jackson, and Klein). Steinernema feltiae (isolate ZAG15) demonstrated the highest biological activity, causing 100% of mortality of larvae and beetles. The lowest activity occurred with H. megidis (isolate Wipsowo), with mortality that did not exceed 58%. At a concentration of 100 infective juveniles/adult, greatest mortality of beetles was observed at 25°C as opposed to lower temperatures for all EPN isolates except the Wipsowo isolate, which showed no statistical significance of mortality among the temperatures tested. At 15°C, adult beetle mortality was concentration-dependent with the S. feltiae isolates ZWO4 and ZAG15. However, neither concentration nor temperature had statistically significant effects on larval mortality.