Background--- The lily leaf beetle, Lilioceris lilii (Coleoptera: Chrysomelidae), a pest of ornamental and native lilies, has been established in North America since 1945 and has spread to five Canadian provinces, all the New England states and New York. The lily leaf beetle overwinters as an adult and feeds on Lilium and Fritillaria species in the spring before mating and laying eggs on the underside of leaves. A thick fecal shield covers larvae, which feed on leaves and flowers, often defoliating plants before pupating in the soil. Young adults emerge in mid-summer and feed before overwintering in leaf litter.

Lilioceris lilii occurs throughout Europe where it rarely attains pest status. The University of Rhode Island Biological Control Laboratory, in collaboration with CABI-Bioscience and colleagues in France, identified a complex of four larval parasitoids, which causes a high level of parasitism throughout Europe. On the basis of parasitoid surveys in Europe and laboratory experiments conducted in the USA and Europe, we determined that T. setifer, L. errabundus, and D. jucunda were safe and likely candidates to control L. lilii.

Parasitiod Releases -- Tetrastichus setifer is likely our best candidate for controlling the LLB in the Northeast. It is widespread throughout Europe and it has been relatively easy to establish in RI, MA, NH, and ME. Lily leaf beetle populations have declined substantially at the two oldest release sites. We last released T. setifer in Wellesley, MA in 2001 where it has heavily parasitized LLB larvae ever since (100% parasitism at peak larval density in 2005). We found similar results in Cumberland, RI where we last released T. setifer in 2002, with 100% parasitism at peak larval density in 2005. From the parasitoids released in surrounding states, we found T. setifer establised in Bridgton, ME in 2004, and this season we recovered overwintered parasitoids from Hudson, NH. We also found a consistently high parasitism rate at Cotuit, MA following T. setifer release this season, so we expect the parasitoid will successfully overwinter. Tetrastichus setifer has also spread several miles from release sites. Working through local garden clubs and the local press, we located 25 lily gardens near our release site in Cumberland, RI. We found T. setifer in 6 of those sites with the most distant recovery over 5 miles from the release plot and 4 of the 6 located at least 1/2 mile distant.

Lemophagus errabundus was found in a lily garden 3/4 mile from our Plainville, MA release site in 2005, indicating that it is not only established from releases in 2003 and 2004, but it has spread a considerable distance. We also released this species in our Kingston, RI plot where we found good parasitism in the weeks following release. Diaparsis jucunda has proven to be more difficult to establish against the LLB. It is found at higher elevations in Europe, and appears well-suited for northern New England, but we have not yet recovered overwintered parasitoids at any of our 2004 and 2005 release sites in RI, MA, NH, or ME. In 2005 we also released LLB larvae parasitized by D. jucunda into our lily plots to determine if this is a better way to establish this species.