An isolated Steinernematid nematode of the species Steinernema scarabaei (ATCC accession No. PTA-6988) is provided which is entomopathogenic to the larvae of scarab beetles, e.g., Japanese beetle (Popillia japonica), oriental beetles (Exomala (=Anomala) orientalis), European chafer (Rhizotrogus majalis), Asiatic garden beetle (Maladera castanea), masked chafers (Cyclocephala spp.), and May/June beetles (Phyllophagaspp). A biopesticide composition is provided which comprises an insecticidally effective amount of Steinernema scarabaei. Biopesticide compositions are described which, in addition to Steinernema scarabaei, further comprise at least one neonicotinoid insecticide, e.g., imidacloprid. Methods are provided for controlling the larvae of at least one species of scarab beetle comprising applying a biopesticide composition to the locus of the larvae wherein the composition comprises an insecticidally effective amount of an isolated entomopathogenic nematode of the species Steinernema scarabaei.