Ecological Entomology (2007), 32, 45–52 © 2007 The Authors Journal compilation © 2007 The Royal Entomological Society 45 Introduction Introductions of exotic plants and phytophagous insects to new geographic areas can result in the rapid evolution of novel plant–insect associations (Strong, 1974; Berenbaum & Zangerl, 1991; Singer et al., 1992; Thompson, 1998). When insects are introduced, either inadvertently or purposely for the biological control of exotic weeds, our ability to predict which native plants are at risk of being colonised by the insect is critical. Relatedness of a novel host to the usual host plant is generally thought to be the primary predictor driving host range expan- sion. Classical biological control of weeds typically involves evaluating a potential control agent’s performance on native plant species related to the target weed, under the assumption that plants closely related to the target are the most vulnerable to a potential host shift (van Klinken & Edwards, 2002). The re- stricted host associations highlighted by Ehrlich and Raven (1964) for several groups of phytophagous insects underscores the importance of phylogenetic conservatism in host-shifting. However, lack of congruence commonly seen between the phy- logenies of host-plant clades and those of the insects that feed on them (Mitter et al., 1991; Dobler et al., 1996; Becerra & Correspondence: Naomi Cappuccino, Department of Biology, Carleton University, Ottawa, Ontario, K1S 5B6 Canada. E-mail: ncappucc@ccs. carleton.ca Potential novel hosts for the lily leaf beetle Lilioceris lilii Scopoli (Coleoptera: Chrysomelidae) in eastern North America CRYSTAL ERNST 1 , NAOMI CAPPUCCINO 1 and JOHN THOR ARNASON 2 1 Department of Biology, Carleton University, Ottawa, Ontario, K1S 5B6 Canada, 2 Department of Biology, University of Ottawa, Ottawa, Ontario, K1N 6N5 Canada Abstract. 1. Introduced insects often incorporate native plants into their diets and might be expected to show a predilection for novel hosts that are phylogenetically related to their normal hosts. The lily leaf beetle, Lilioceris lilii (Coleoptera: Chrysomelidae), is an introduced pest of cultivated lilies. Oviposition behaviour, larval behaviour, and development of L. lilii was examined on a range of potential host plants, as well as on the normal host, Asiatic hybrid lilies Lilium sp. 2. Neonate larval feeding behaviour was quantified on 15 food plant species: 10 from the Liliales, three from the Asparagales and two eudicots. Larvae fed plants closely related to the genus Lilium were more likely to initiate feeding, less likely to abandon their food leaf, and consumed more leaf area. 3. In no-choice tests, females oviposited on the novel hosts Lilium philadelphicum, Medeola virginiana, Clintonia borealis, Streptopus amplexifolius, and Polygonatum biflorum; however, all but L. philadelphicum received very few eggs. Non- Lilium novel hosts were not used for oviposition when presented along with Asiatic lilies in choice tests. 4. A single individual was reared to the adult stage on the novel host S. amplexifolius. Several larvae survived to the pupal stage on M. virginiana, although no adults emerged from those pupae. Larvae reared on the native wood lily L. philadelphicum performed equally well or better than on the Asiatic cultivar. 5. Our results indicate that the lily leaf beetle poses a threat to native Liliaceae. Several native Lilium species, including L. philadelphicum, are threatened or endangered in certain jurisdictions throughout their range; these species should be monitored closely for colonisation by the beetle. Key words. Exotic insects, host shifts, host range expansion, Liliales.