HOST PREFERENCE AND LARVAL PERFORMANCE OF THE SALICYLATE-USING LEAF BEETLE PHRATORA-VITELLINAE

Larvae of Phratora vitellinae (Coleoptera: Chrysomelidae) convert sali cyl glucosides from the host plant into a larval defensive secretion w ith salicylaldehyde. This secretion repels generalist predators. Willo ws vary greatly in the concentrations of salicyl glucosides in their l eaves. One may predict that P. vitellinae prefers and survives better on plants that contain more salicyl glucosides. We determined the amou nt of larval secretion, host preference, larval growth, and larval sur vival of P. vitellinae on Salix myrsinifolia, S. pentandra, and S. phy licifolia. We also measured feeding rates of three natural predators o n P. vitellinae larvae feeding on different hosts. Salix pentandra and S. myrsinifolia contained substantial amounts of salicyl glucosides, but S. phylicifolia contained very little of them. Phratora vitellinae larvae produced more secretion on S. pentandra than on S. myrsinifoli a. They produced little secretion on S. phylicifolia. Adult beetles pr eferred S. myrsinifolia over S. pentandra and S. pentandra over S. phy licifolia. Larvae grew most rapidly on S. myrsinifolia and S. pentandr a. Their growth was slowest on S. phylicifolia. The larval survival wa s similar on S. myrsinifolia and S. phylicifolia, but it was significa ntly lower on S. pentandra. The natural predators fed equally well on P. vitellinae feeding on S. myrsinifolia and S. phylicifolia. Thus, th e host preference of P. vitellinae did not correspond to larval surviv al on these hosts, but rather to larval growth. Larval survival of P. vitellinae was not related to the amount of defensive secretion. Natur al predators were not repelled by the host-derived defensive secretion . We discuss the implications of these findings for the evolution of h ost plant use in this herbivore.