Apparent Mutualism Between Verticordia nitens and V-Aurea (Myrtaceae) and Their Oil-Ingesting Bee Pollinators (Hymenoptera, Colletidae)

Abstract

The prominently-displayed flowers of Verticordia nitens and V. aurea are unattractive to most insect pollinators and yet apparently serve as the sole source of pollen and nectar for two species of solitary bee. Euryglossa (Euhesma) morrisoni forages exclusively on V. nitens and E. (E.) aureophila forages exclusively on V. aurea. These bees carry much pollen on their bodies and appear solely responsible for seed set of 9-31% of ovules, with negligible seed set by V. nitens in the absence of E. morrisoni. Each anther of both Verticordia species releases pollen in copious amounts of oil (pollenkitt) beneath a hood-like appendage which terminates in a spout. Female bees ingest the pollen-oil mixture by touching the appendages with their glossae, and nectar by lapping the floor of the hypanthium. Most of the oils are isopentyl esters of the fatty acids, palmitic, stearic, arachidic (the major component of V. nitens) and behenic (the major component of V. aurea). These oils, as well as significant amounts of glucose, fructose and proline, are also present in the crop of E. morrisoni. The ability ofE. morrisoni and E. aureophila to remove and utilise pollen, oil and nectar from the flowers, their effectiveness as sole pollinators, and flower colour mimicry by E. morrisoni, together suggest an obligate mutualism between these bees and their Verticordia hosts.