THE EVOLUTION OF HOST-PLANT USE AND SEQUESTRATION IN THE LEAF BEETLE GENUS PHRATORA (COLEOPTERA, CHRYSOMELIDAE)

Leaf beetles in the genus Phratora differ in host plant use and in the chemical composition of their larval defensive secretion. Most specie s specialize on either poplars or willows (family Salicaceae), but two species feed on birch (family Betulaceae). Phratora vitellinae utiliz es salicylates from the host plant to produce its larval secretion, wh ich contains salicylaldehyde, while other Phratora species produce an autogenous secretion. To reconstruct the evolutionary history of host plant use and the larval secretion chemistry in this genus, we sequenc ed 1383 base pairs of the mt cytochrome oxidase I gene for six Europea n and one North American Phratora species and three outgroup taxa. Boo tstrap values of the complete nucleotide sequence were 99-100% for six of eight nodes in the maximum parsimony tree. They were 71% and 77% f or the two other nodes. The maximum parsimony tree and the maximum lik elihood tree based on nucleotide sequence showed the same relationship s as a maximum parsimony tree based on the amino acid sequence. Beetle phylogeny overlapped broadly with host plant taxonomy and chemistry, and it revealed historical constraints influencing host plant use. How ever, there was one host shift from the willow family (Salicaceae) to the birch family (Betulaceae). The use of host plant phenol glycosides for the larval defensive secretion evolved along the lineage that led to P. vitellinae. Phratora vitellinae feeds on the taxonomically wide st range of host plants, which are characterized by moderate to high l evels of salicylates. The results support the hypothesis that the use of salicylates for the larval secretion evolved twice independently in chrysomeline leaf beetles.