Euglossine bees

The bees must have some important role for these chemicals, for without them their lives are shorter. They possess remarkable structures for collecting and storing scents and devote enormous effort to the task. Why do they do this What do they do with the chemicals they collect Unfortunately, we know too little about euglossine bees to answer these questions definitively. It is easy to attract and trap male bees using synthetic fragrance chemicals such as cineole as bait, but females are considerably more difficult to find. As a result, several euglossine species are known only through male specimens, and much in these creatures lives remains hidden from our view. 

We do know that some male euglossine bees mark out territories, either individually or in groups, and then attract females to... 

Janzen, D. H. (1971). Euglossine bees as long distance pollinators of tropical plants. Science 171 203-205. 

Lunau, K. (1992). Evolutionary aspects of perfume collection in male euglossine bees (Hymenoptera) and of nest deception in bee-pollinated flowers. Chemoecology 3 65-73. 

Williams, N. H. and Whitten, W. M. (1983). Orchid floral fragrances and male euglossine bees methods and advances in the last sesquidecade. Biological Bulletin 164 355-395. 

Molecular phylogeny and floral fragrances of male euglossine bee-pollinated orchids a study of Stanhopea (Orchidaceae). Plant Species Biology 14 ... 

Figure 2.4(C). Allometric scaling of flight metabolism in Euglossine bees (Euglossa, Exaerete, Eulaema, Eufriesea) plotted on the same log-log scale as the maximum flight muscle hexokinase H K max activity. Each point corresponds to the average value of a single species. Open circles represents V02 data measured in nine species by Casey et al. (1985). Filled circles represents hexokinase maximal activity measured in 28 species by Darveau, Suarez, and Hochachka (unpublished data). Note that no difference in slopes between the two data sets could be detected. (Unpublished data are courtesy of R.K. Suarez and C.A. Darveau.)...

Males of neotropical euglossine bees (Apidae), called orchid bees, collect odoriferous substances from flowers of orchids and other plants. The floral scents of these species display relatively simple chemical compositions dominated by one or two major components, mostly terpenoids and aromatic compounds such as cr-pinene, 1,8-cineol, eugenol, -dimethoxybenzene (35), 2,3-epoxygeranyl acetate (36), nerolidol, 4-methoxycinnamaldehyde (37), and benzyl benzoate.113 Since the orchid bees have odor preferences, their collection of fragrances leads to specialized pollination of particular plant species. Male bees absorb the floral volatiles with their tarsal hairs, form species-specific bouquets, and finally accumulate them in their hind tibial pouches. These bouquets have potential roles in courtship displays and marking territories.114 115... 

Several species of orchids are pollinated by euglossine bees (Dodson et al., 1969 Hills, 1989 Williams and Whitten, 1983). In one example, pollination appears to involve a relatively simple monoterpene. The essential oil complement of Stanhopea pulla, which consisted mostly of -limo-nene oxide (78) (Fig. 19.17), 1,8-cineole (10), and an unidentified monoterpene, varies both quantitatively and qualitatively depending on the time of day. Maximum fragrance production occurs early in the morning. The euglossine bee involved responds to -limonene oxide (78) in mixtures of E- and Z-limonene oxide (Fig. 19.17) (Hills, 1989). 

The complement of volatile substances produced by most species of orchids is highly specific and this specificity appears to preclude hybridization in many cases (Hills et al., 1972). Although some species of orchids are pollinated by several species of euglossine bees, most are pollinated by a single species of bee (Ackerman, 1983). 

There is controversy about the exact role of the odoriferous compounds collected by the male bees, but it is likely that they are involved in attraction of other euglossine bees or converted into sexual (aggregation) pheromones. It has been suggested that males use the compounds and various aspects of behavior to attract other males. This makes a small swarm of bees, and the females are attracted. This is similar to lek behavior in birds (Harbome, 1982, 1989). 

Although the orchids are visited only by euglossine bees, the bees are known to visit flowers of plants of other families with similar chemistry (Williams and Dodson, 1972). Although the bees have undoubtedly been important in determining the course of evolution in the orchids, factors in addition to those associated with the orchids have been important in the evolution of the bees (Ackerman, 1983). 

Ackerman, J. D., Specificity and mutual dependency of the or-chid-euglossine bee interaction, Biol. J. Linn. Soc., 20, 301-314 (1983). 

Williams, N. H. and C. H. Dodson, Selective attraction of male euglossine bees to orchid floral fragrances and its importance in long distance pollen flow. Evolution, 26, 84-95 (1972). 

Male Euglossa imperialis and Eulaema meriana perch on tree trunks in their territories and display in such a manner that release of a sex attractant pheromone from the tibiae is likely (Kimsey, 1980). Although the chemicals from orchids that attract male euglossine bees have been characterized, the chemical structure of the pheromone released by the males has not been determined, nor, indeed, has its presence been proven. This is a crucial missing link in the orchid bee story. 

---