Chemoecology 3 (1992) 65-73 65 Evolutionary aspects of perfume collection in male euglossine bees (Hymenoptera) and of nest deception in bee-pollinated flowers Klaus Lunau Institut für Zoologie der Universität, Universitätsstr. 31, D-8400 Regensburg, Federal Republic of Germany Received January 25, 1992 / Revision accepted April 20, 1992 Summary A fascinating pollination system has been evolved between perfume producing flowers and perfume collecting male euglossine bees in the neotropics. Detailed in- vestigations have contributed to an understanding of the in- teractions between euglossine males and flowers as a pollina- tion system. The role which the collected perfume plays in the reproductive behaviour of euglossine bees is not fully un- derstood. A favoured hypothesis suggests that the collected fragrances are used as precursors for male sex pheromones and thus serve to attract conspecific males or females. It is not known how perfume collection behaviour evolved. Here, an evolutionary approach presents a new hypothesis which suggests that the evolution of perfume collection in euglos- sine males is based upon pre-existing signals which were at- tractive to females and males. It is further suggested that, at the evolutionary outset, flowers mimicked nest sites to de- ceive nest-seeking euglossine bees. In addition, a compara- tive study was undertaken on the phenomena of nest-mim- icking flowers in related bee families. Key words euglossine flowers, perfume collection, eu- glossophily, floral fragrant exudates, nesting behaviour, mating behaviour, bee pheromones, nest mimicry, signal evolution, Hymenoptera, Apidae, Euglossinae Introduction One of the most striking pollination systems is that in the American tropics between the euglossine orchids and male euglossine bees in which intricate mechanisms of pollen transfer have evolved. The main floral attractant and reward consist of fragrant exudates, such as mono- and ses- quiterpenes and aromatics (Williams & Whitten 1983; Gerlach & Schill 1991). The euglossine males intensively work at the flowers to rub off the perfume oils and, while hovering, trans- fer them to storage organs of the hind legs. Some orchids have evolved extraordinary means of physically transferring polli- naria to the bee by a triggering mechanism which propells the pollinarium with considerable force to a specific transport area on the bee. Mechanisms of pollen transfer which depend on slipping and falling are correlated with complex floral morphology (Dr essler 1968). More than 650 neotropical orchid species (Orchidaceae) are pollinated solely by male euglossine bees (Ackerman 1983); Stanhopea, Gongora, Catasetum and Co- ryanthes are the most prominent genera. Production of floral fragrant exudates and pollinator service by male euglossine bees are not restricted to orchids. Spathiphyllum cannaefol- ium (Araceae), Gloxiniaperennis (Gesneriaceae) (Vogel 1966), and Daleehampia spathulata (Euphorbiaceae) (Armbruster & Webster 1979), for example, are non-orchid euglossine flowers. The males of all five genera of Euglossinae (Hymenoptera, Apoidea, Apidae, Euglossinae), Euglossa (approx. 100 sp.), Eufriesea (52 sp.), Eulaema (13 sp.), Exaerete (5 sp.) and Aglae (monotypic) possess specific perfume storage organs on the tibiae of the hind legs. The females of the latter two gen- era are cleptoparasitic on other Euglossinae. Male euglossine bees collect fragrant compounds also from non-floral sources including decaying wõod, rotting fruits, tree barks, animal feces (Ackerman 1989). Euglossine males can even be baited by a number of chemicals when presented in pure form in field trials. Testing compounds which are common floral fra- grances, some baits attract a large number of euglossine spe- cies, whereas other baits attract only one species. Some baits do not attract euglossine males, instead they appear to modify the attractiveness of other compounds. Multi-compound halts attract fewer species (Dodson et al. 1969; Williams & Whitten 1983; Ackerman 1989). The species-specific combinations of floral fragrance compounds can act as an ethological isoläting mechanism via pollinator specificity (Hills et al. 1972). The euglossine males soak up the fragrant exudates with foreleg brushes and transfer them to the storage organs. Following perfume collection in the early morning, male Euglossinae search for mating territories. They prefer clearings to display on tree trunks (Vogel 1966; Kimsey 1986; Dressler 1982) where they evaporate odours by wingfanning (Vogel 1966). Schemske & Lande (1984) were the first to de- monstrate that the access to fragrances significantly affected the display and territorial behaviour of male Euglossa imper- ialis. © Georg Thieme Verlag Stuttgart - New York
