Pollinators of Eucalyptus regnans (Myrtaceae), the world's tallest flowering plant species

Abstract

Insect visitors to the flowers of Eucalyptus regnans F.Muell. in a remnant natural stand were classified into 33 functional pollinator groups according to taxonomic affinity and body size. In total, 92% of insects caught were dipterans; however, most of these were small and did not contribute significantly to pollination. For the majority of taxa, which have short mouthparts and therefore need to intrude themselves into the flower while feeding on nectar, there was a highly significant relationship between body length and the number of E. regnans pollen grains carried on the body. Mean pollen loads ranged from 20 grains per insect for sepsid flies to 84 000 for large tachinid flies. An index of pollen-deposition potential, which is based on population size and pollen load, suggested that the larger tachinid, calliphorid and syrphid flies were the most important pollen vectors and that larger sphecid wasps also played a significant role. Many taxa appeared to contribute little to pollination because they were uncommon and/or did not carry large quantities of pollen. A convention is proposed whereby groups are weighted according to their contribution to total pollen-deposition potential. For E. regnans, a ratio of 5 Diptera/1 Hymenoptera + (Coleoptera/Lepidoptera) is described, with the taxa in parentheses contributing less than 10% of the total.