PERFORMANCE OF GALERUCELLA-CALMARIENSIS (COLEOPTERA, CHRYSOMELIDAE) ON DIFFERENT NORTH-AMERICAN POPULATIONS OF PURPLE LOOSESTRIFE

The success of a biological weed control program depends on the abilit y of control agents to develop on various genotypes of their host plan ts, thereby reducing the competitive ability of the target plant speci es. We studied the performance of the chrysomelid beetle Galerucella c almariensis L., introduced as a biological control agent of purple loo sestrife, Lythrum salicaria L., on plants from 3 different North Ameri can populations. Plants for the experiments were obtained from Ithaca, NY; St. Paul, MN; and Salem, OR, representing different climates and colonization histories. We studied the survival and impact of G. calma riensis at 3 herbivore densities with plants grown under identical con ditions at Ithaca. Plant growth and biomass allocation patterns were s ignificantly different among the 3 tested populations. Survival rates of the leaf beetles (egg to adult) were not significantly different am ong sites or among herbivore attack levels. Herbivory caused significa nt reductions in plant height, leaf, shoot, root, and total plant biom ass with increasing attack levels. We found no significant interaction of herbivory and plant origin. Plants compensated for the loss of pho tosynthetic tissues by replacing foliage at the expense of below groun d storage, thus, herbivory altered the biomass allocation pattern of L . salicaria. This might have important implications for other control agents attacking the roots of L. salicaria.