Nemasys G contains live nematodes (Heterorhabditis bacteriophora) in their vigorously infective stage. These nematodes attack pest larvae by entering their natural body openings. Once inside, they release symbiotic bacteria that quickly kill the insect. Reproduction inside the insect releases a new generation of hungry, infective juveniles that disperse in search of further prey.

Nemasys G is effective against the larvae, or grubs, of European chafers, Oriental beetles and Japanese beetles.