Low fruit set in an endangered tree: pollination by exotic bumblebees and pollen resource for relictual native bees

Many endangered plants are susceptible to pollination failure due to their rareness. We studied the threatened Chilean tree Legrandia concinna (Myrtaceae) with melittophilous pollen-only flowers and the pollen loads of Manuelia postica and asked: Do bees guarantee fruit set? What is the role of the endangered plant as a pollen source for M. postica? Only bees of the relictual endemic Manuelia postica and introduced Bombus terrestris and honeybees visited the flowers. Overall flower visitation was very low and so was fruit set. Exotic B. terrestris was the only effective pollinator. The small native M. postica scarcely contributed to pollination and mainly used pollen of L. concinna to rear offspring in the resource-poor Nothofagus forest: pollen of 19 flowers was sufficient to feed a single larvae. Reintroduction of trees of L. concinna as a measure of species protection would also benefit the maintenance of native populations of M. postica. We assume that the introduced bumblebees displaced native Bombus dahlbomii as pollinators of this red list tree species.