Male Euglossa imperiialis (Apidae, Euglossini) were marked after capture at cineole, a compound in orchid floral fragrances. Recaptures revealed that a large number of males may be available for pollination of a given orchid and that individual bees may remain at one locality throughout a morning and may be recapturable at that site over a period of several days. THE POPULATION BIOLOGY of many tropical plant species is influenced by insect pollinator species. This situation is especially true of many neotropical orchids, where floral fragrances of a given species attract male bees of only one or a few species in the tribe Euglossini. The effective orchid population size is therefore related to (1) distances between orchids and (2) distances flown by the pollinating male euglossine bees. The spectacular pollination of orchid flowers by the male bees has been described in some detail (see Williams and Dodson 1972, for review), but little else is known about the males' life habits. They leave the nests after hatching and do not return (Dodson 1966, Roberts and Dodson 1967). At least some males spend the night sleeping in flowers (Dodson 1966), suggesting that foraging could begin from a different locality each day (Williams and Dodson 1972). Females of some species are communal in their nesting habits, but no worker and reproductive castes occur as are found in the Bombini, Meliponini, and Apini. Each female builds and provisions her own nest cells and lays her own egg therein. Such is the case for Euglossa imperialis and probably E. ignita; females of other species (e.g., Euglossa dodsoni) are solitary, with each female building her own nest (Roberts and Dodson 1967). The foraging behaviors of the sexes are possibly very different. Females have a definite "home," make regular flights to and from the nest (Janzen 1971), and do not visit orchid flowers, while males visit orchids as well as nectar hosts. The hypothesis that male euglossines may fly long distances between orchids (see Dressler 1968, Williams and Dodson 1972) is founded on several observations: (1) Janzen (1971) found that female Euplusi,a surinamensis may return to the nest when displaced as much as 23 km; the speedy return suggests that "bees were released in an area known to them and therefore probably within their foraging range." (2) The bees are very strong fliers, indicated by flights across 1-5 km of water (female Euplusia and Eulaema observed by Janzen 1971, sex not mentioned Dressler 1968) or 1000 m above normal foraging locations in the Andes (sex not mentioned, Dodson, in Dressler 1968). (3) Widely dispersed orchid individuals are presumably maintained by pollinators traversing considerable distances (Williams and Dodson 1972). Failure to recapture more than one or two marked male bees at a given point indicates (a) that bees are present in extraordinarily large numbers and recapture of a marked bee is an improbable event, (b) that bees range great distances and might therefore rarely return to a given location (Williams and Dodson 1972), or, less likely, (c) that marking is so traumatic that the bee dies or flees. Williams and Dodson (1972) further speculate that a large male euglossine bee should be capable of flying 24 km within a day, 40 km in a few days, and 80-90 km in a few days or a week. Such flight distances are certainly possible, for a honeybee (Apis mellif era ) has been shown to fly over 100 km/day in her many flights to and from the hive (von Frisch 1967). However, the actual distances flown by male euglossines are unknown, and preliminary mark-and-recapture experiments which I conducted during March 1972 at the Tropical Science Center building, Rincon de Osa, Costa Rica, suggest that the activity of some bees may in some instances be quite local. Between 0700 and 1130 on 4 March at a location on the Holdridge Trail, I captured 601 Euglossa males of approximately 15 species which were attracted to 4 cm2 blotters placed on the ground and sprinkled with cineole, one of several compounds which has been identified in orchid floral fragrances (Hills, Williams, and Dodson 1968). BIOTROPICA 7(1): 71-72 1975 71 This content downloaded from 207.46.13.57 on Fri, 09 Sep 2016 04:22:31 UTC All use subject to http://about.jstor.org/terms Seventy-five bees were marked with unique color combinations, and the remainder were simply marked with a spot of silver paint on the thorax. During the morning of 5 March I returned to the same location, again put out the blotters with cineole attractant, and captured 191 bees. On this day, detailed observations were made of the species E. imperialis Cockerell. I captured 126 individuals of this species; 22 had been marked the day before. Assuming the same proportion (126/191 0.66) of E. imperialis present in the 4 March sample where records for each species were not kept, and making all the assumptions of mark-recapture population estimates (including no immigration or emigration), the approximate number of imperialis males foraging at this locality was 2270. On 6 March I placed blotters with the cineole attractant at locations 5, 10, 15, and 20 minutes walking distance from the marking location (20 minutes was approximately 1.5 km), and sampled each location every 30-45 minutes between 0730 and 1100 for E. imperialis. Marked bees were still present in considerable numbers (see table 1). (The TABLE 1. Data on bee marking. 6 March distance from marking location 5 March E marking location ? No. marked bees 22 7 3 0 0 Total no. bees 126 54 60 10 16 Proportion marked 0.175 0.130 0.050 0.000 0.000 decreasing proportion of marked bees at increasing distances from the marking location probably reflects the increasing area over which marked bees could forage.) Observations of the individually marked bees indicated that the same bee might return to the cineole bait several times in the same morning. For example, a bee marked at 0750 was observed at the bait again at 0955 and 1032. Orchid flowers are undoubtedly less attractive than the bait, for one never sees 50 bees at the same flower. In addition, the data presented here are subject to the biases of small sample sizes, but especially to the biases introduced by the use of supernormal concentrations of attractants which could conceivably alter normal foraging habits. Under the experimental conditions used, the data reveal that a large number of male bees (E. imperialis were especially abundant) may forage at one site and that individual bees may remain in one locality throughout a morning and may be recapturable over a period of several days. This finding is in contrast with the extremely low recapture rates published by others (Williams and Dodson 1972), and should encourage further study of the distances flown by male euglossines and of the role which the bees play in the population biology of orchids.