Wasp-Pollinated Species of Caladenia (Orchidaceae) in South-Western Australia

Abstract

Twelve of the 40 Caladenia species of Western Australia have been observed to attract male wasps (Tiphiidae; subfamily Thynninae) by visual and pheromonal mechanisms. Floral colours are predominantly combinations of green, cream and brown. Labella bear dark maroon tips or dark calli on the upper surface which are visual wasp equivalents. Glandular areas on perianth tips are demonstrated to be sources of sexual attractants in some species. Flower form and position are adjusted to the flight behaviour of the wasps. Each Caladenia species appears to attract and be pollinated by only one wasp species at the orchid site although there is limited evidence of geographic pollinator replacement in some species. Sexually attracting Caladenia species form occasional hybrids with food- advertising species. Divergent pollination mechanisms have not resulted in complete genetic isolation.