Bee arrival at two Costa Rican female Catasetum orchid inflorescences, and a hypothesis on euglossine population structure

Abstract

It is well known that Cataseturn flowers are pollinated by male euglossine orchid bees (Criiger 1865, Darwin 1877, Dodson 1962, Pijl and Dodson 1966). The bees remove several chemicals from Cataseturn (and other orchid) flowers with brushes on their front feet, transfer the chemicals to special grooves in their hind tibiae, and use them for unknown purposes in their own physiology (Dodson et al. 1969). Degradation products of the chemicals appear in mandibular gland secretions (N. H. Williams pers. comm.) but the secretions are of unknown function. Just as with other orchids pollinated by euglossine orchid-bees no one has examined the quantities of bees that visit Catasetum inflorescences in a natural habitat (see Williams 1978 for a thorough bibliography of orchid-bee papers). Here I describe the visitors and pollinators at two sequential Sflowered female inflorescences on one ~atasetum maculatum orchid. The central axis so as to produce approximately equal numbers of degrees between each of the 5 lines of approach. The buds of the first inflorescence began to open on 15 May 1979, the first odors were produced by the most proximal flower on 18 May, and the five open unpollinated flowers ceased odor production after the morning of 27 May. The buds of the second inflorescence did the same; the most proximal was the first flower to attract bees (10 July). The last day of attraction was 15 July, and the pollinated flowers stopped producing odor on the day of pollination. No rain fell from 21 through 28 May, though the rainy season had begun on 25 April. The weather was sunny and breezy. During 10-15 July no rain fell in the morning but there was afternoon rain and extensive cloudiness during the day and evening. During the dry season at SRNP, C. maculatum is leafless and does not bear flowers.