Population decline
There are no natural predators or parasites of lily leaf beetle in North America. In 1996, University of Rhode Island began testing the effectiveness of biological control of lily leaf beetle using six natural parasitoids from Europe. CAB International Bioscience Switzerland Center has also participated in this project from 1998 till 2001. The European parasitoid wasp "Tetrastichus setifer" was used in Massachusetts from 1999 to 2001; the experiment showed reduction of the beetle population. Population decline was also observed at another experiment site in Rhode Island. In 2003, another parasitoid, "Lemophagus errabundus", was released in Massachusetts and is now established in the region. Similar parasitoid releases have been made in Boston with positive results.