Lily Leaf Beetle Biological Control Update
The lily leaf beetle, Lilioceris lilii (Coleoptera: Chrysomelidae), a pest of ornamental and native lilies, has become established in Piscataquis County a few years ago. It has been in North America since 1945. 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. Many home gardeners have considered replanting their lilies to another type of perennial to get away from the pesticide sprays needed to control this pest. Now there is hope on the horizon for an effective biological control.
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.
Tetrastichus setifer is likely the 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. They 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). They 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, they found T. setifer establised in Bridgton, ME in 2004. Tetrastichus setifer has also spread several miles from release sites.
Lemophagus errabundus was found in a lily garden 3/4 mile from their 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. They also released this species in our Kingston, RI plot where they 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 they have not yet recovered overwintered parasitoids at any of their 2004 and 2005 release sites in RI, MA, NH, or ME. In 2005 they also released LLB larvae parasitized by D. jucunda into their lily plots to determine if this is a better way to establish this species.
Until the parasitoids move into the area here are some suggestions for control of the lily leaf beetle. If you only have a few plants in your garden, hand-picking adults and eggs can be effective (we prefer not to handle larvae, although there is no danger in doing so). The insecticides carbaryl (Sevin) and malathion are effective on adults and larvae. However, carbaryl is highly toxic to bees and malathion is also toxic to many non-target insects. To date, our material of choice for treating flowers is neem, an insecticide based upon extracts from the neem tree. Neem can be purchased at garden centers under the trade names Turplcx, Azatin EC, Margosan-0, Align and BioNeem. Neem kills larvae and repels adults. Neem is most effective on first instar larvae; it must be applied every five to seven days after egg hatch. The insecticide imidacloprid also provides effective control. It is available in several formulations from Bayer including foliar sprays, soil drenches, and fertilizer stakes.
When trade names are used for identification, no product endorsement is implied, nor is discrimination intended against similar materials.
Source: Casagrande, R. and L. Tewksbury, Department of Plant Sciences, University of Rhode Island, Northeastern PIM News, May 2006 http://northeastipm.org/ipm_news_popover.cfm?id=905
And URI Green Share Factsheets, University of Rhode Island Plant Science Department, 2002, http://www.uri.edu/ce/factsheets/sheets/lilyleafbeetle.html.