Eulaema meriana, also known as Merian's orchid bee, is a large-bodied bee species in the tribe Euglossini, otherwise known as the orchid bees. The species is a solitary bee and is native to tropical Central and South America. The male collects fragrances from orchid flowers, which it stores in hollows in its hind legs. Orchids can be deceptive by mimicking the form of a female and her sex pheromone, thus luring male bees or wasps. Pollination will take place as the males attempt to mate with the labellum, or the tip petal of the flower. Male E. meriana are territorial and have a particular perch on a tree trunk where it displays to attract a female. After mating, the female builds a nest with urn-shaped cells made with mud, feces, and plant resin, and provisions these with nectar and pollen before laying an egg in each. These bees also have complex foraging and wing buzzing behaviors and are part of a mimicry complex.
Description Eulaema meriana resembles a bumblebee in appearance and is covered in short dense hairs. At first glance Eulaema bees look like large bumblebee queens. They are relatively large bees with faint metallic colorations. The head of the bee is black, and the thorax brownish black with a large, glossy black scutellum. Their abdomen is black with three transverse pale yellowish bands on the anterior half, and the posterior third is reddish brown. E. meriana also possess membranous wings that are dark at the base and paler at the tips. The legs are black and the tibia of the hind legs are much thicker. Males possess hollows on their hind legs, while females have pollen baskets. In general, the species have long tongues that are thought to be an evolutionary adaptation that favors nectar collection. The large body size is thought to allow the bees to fly in cooler, rainy conditions and continue foraging. It has also been suggested that the larger body size can help them forage for longer distances.
Taxonomy and phylogeny Eulaema meriana is part of the order Hymenoptera, which includes ants, bees, wasps, and sawflies.
E. meriana is part of the tribe Euglossini within the subfamily Apinae of the family Apidae. Euglossini are part of a group known as corbiculate bees, a group that also includes honey bees, stingless bees, and bumble bees. Members of this group have concave hind legs ("corbiculae") that are used for transportation of materials used in nest construction and cell provisioning.
Orchid bees do not include advanced social species, in contrast to the other corbiculate Apinae, that form colonies with morphologically discrete queen and worker castes.
Orchid bees are considered to be key species in lowland forests because they are pollinators of specific tropical plants, especially orchids. It is in fact the males that perform cross-pollination. They have also been targets of conservation, and the diversity of the euglossine bees as a whole is being affected by habitat fragmentation. E. meriana is closely related to its sister species, E. bombiformis.
Distribution Eulaema meriana is native to Panama, Colombia, Venezuela, the Guianas, Ecuador, Peru, Bolivia and Brazil. It is found in forests in the Amazon basin but is replaced in the Atlantic coastal forest by Eulaema niveofasciata and Eulaema flavescens. The genus Eulaema itself ranges from Mexico to northern Argentina.
Nests
General nest architecture Nest entrances have a mud wall or ceiling at the entry point, with a very narrow entrance hole (about 15 mm in diameter). The nests contain a pedicel made out of mud, and a number of urn-shaped brood cells fused together. The pedicel increases in size as the overall size of the nest increases as well. The pedicel is built first and its anterior surface is what forms the back of the first brood cell, which is made of a thick layer of mud and has an average volume around 4.8mL. Cell structures have been observed to be similar across nests. Each cell is fused to the wall of the previous cell, and new cells are often observed to be attached along the same plane. The cells are then covered with a thin layer of feces and lined with resin that is extended past the opening to form a collar. After oviposition by the female, the resin collar is pushed inward by the female and then covered with a layer of mud. In larger nests, once a layer of cells is complete, the surface is covered with mud to make a new floor for the next layer of cells to be built.
Nest initiation and construction
After mating, a female usually chooses a cavity as its nesting site. If the entrance is too large, a mud wall about 8-9mm thick may first be built in which a hole about in diameter is made. The mud is gathered in small balls by the mandibles, transferred progressively to the fore, mid and hind legs, and deposited in the pollen basket on the hind leg. About six balls make a load, three in each basket and the female flies back to the nest site. Inside the cavity, a pedicel is constructed on which an urn-shaped cell is built. The mud hardens as it dries.
Initiation of a nest begins with mud collection for the mud wall, entrance, pedicel, and first brood cell. This process can take up to four days. Therefore, all trips on the very first day of nest construction are devoted to mud collection. After the first brood cell is nearly complete, the female will begin to collect both mud and resin, which will be used to line the cell on the second day. After the cell is lined, almost no mud is collected on the third day. A female will spend almost three quarters of her time foraging for larval food collection, and the rest for resin collection. Once the brood cell is complete, oviposition will occur, the collar will be pushed in, and the cell will be covered with mud. The construction of additional cells follows a similar timeline, although there is less mud collection now that the mud wall and entrance have been built. It was noted by Cameron and Ramirez in a study done on the nest architecture of the E. meriana that less time was required to build successive cells after the first. Some nests were also observed to be reused. Clusters of older cells and decomposing females were found in some of the cells, covered with a layer of mud.
Brood cell construction Each brood cell is filled two-thirds of its volume with a pale yellow, sticky pollen/nectar mixture. Females returning to the nest with this sticky substance attached to their corbiculae deposit it into the only open brood cell. The female E. meriana follow a specific ritual after placing this pollen mixture into a cell. They make a rotation with the posterior part of the body inside the cell and forelegs around the resin collar. It is suggested that this allows the pollen mixture to be pushed down and packed into the cell. Other materials like mud, feces, and resin are deposited in the nest. Mud and feces can be found deposited on the floor of the nest, while resin is stuck onto a cavity wall near the pedicel.
While the actual size of the nest cavity varied in the study conducted by Cameron and Ramirez, the brood cells of all the nests studied were uniform in size, shape, and structure. The cell structures were also similar to the cells built by other Eulaema species.
Colonies Eulaema meriana typically begin nests alone, and they remain solitary. Occasionally they form parasocial colonies with two or more females that are from the same generation and may even be sisters.
Females work inside the nest at night, constructing cells and ovipositing. One egg is laid in each provisioned cell, and oviposition occurs after the provisions are tamped into the cell. Egg laying happens quickly as the female backs into the cell, holding the collar with her forelegs and inserting her posterior end into the cell. After laying the egg, the female pushes the resin collar in and spends a few hours covering the cell with mud. After this, the female begins to work on building a new brood cell.
Larger nests can have multiple females. Females may use the same site over many generations and continuously build upon the nest. In one large nest studied in Ecuador consisting of 76 cells, two females were found together in the nest for at least 17 days. One of the females carried pollen nectar loads on her corbicula and deposited it into the only open cell. A second female carried mud, covering dead females with mud and working on the nest construction. This suggests some level of social plasticity among these solitary bees.
For single female nests, each cluster of cells represents the reproductive output for one female. One female on average will construct and oviposit over four or five brood cells before disappearing and leaving the nest. Egg development is rather long, with adults observed to be emerging 100–165 days after oviposition.
Pollination As in other species of orchid bee, both the male and female visit flowers to feed on nectar. Besides this, the male has a mutualistic relationship with one or more species of orchid. To persuade the male to visit its flowers, the orchid produces fragrances of a particular chemical composition attractive to a specific species of bee that is exactly the right size and shape to pollinate the flower. Stanhopea orchids are mostly pollinated by large Eulaema bees, Euglossa species often being too small for the purpose. In more primitive species in the genus Eulaema, the orchid pollinium, a packet of pollen, adheres to the male bee as it reverses out of the flower having collected the fragrance. In more advanced species, there is a fall-through mechanism in which the bee loses its footing on some oil droplets while collecting the fragrance and the pollinium adheres to the bee as it slithers out of the flower. E. meriana has been observed visiting Stanhopea florida and pollinating Stanhopea candida, Stanhopea costaricensis and Stanhopea tricornis. It also pollinates Catasetum macrocarpum and Notylia pentachne. It is also the only bee species thus far reliably documented as a pollinator of a species of Vanilla – Vanilla grandiflora.Lubinsky P, Van Dam M, Van Dam A (2006) Pollination of Vanilla and evolution in Orchidaceae. Lindleyana. 75:926–929 In a study to identify which insects pollinated the flowers of the Brazil nut tree (Bertholletia excelsa), it was found that the flowers were visited by a number of bee species, including E. meriana, which visited the tree early in the day. Both males and females were observed collecting nectar from the base of the flower's lower lip. The study concluded that E. meriana played a part in the pollination of the Brazil nut flowers but that other bee species, Eulaema mocsaryi and Xylocopa frontalis, were of greater importance, thus E. meriana are not required to pollinate Brazil nut flowers. Nevertheless, in commercial Brazil nut tree plantations, successful pollination depends on the plantation being surrounded by intact primary forest with its epiphytic orchid population to supply a sufficient number of pollinating bees for the large number of flowers.
Fragrance collection Male orchid bees have a large hind tibia with pouches where they store fragrances. Adult male bees spend much of their time filling their pouch with the volatile fragrances found at orchid flowers. This behavior has given rise to the “pollination syndrome”, where males pollinate about 650 orchid species. They apply lipids to these fragrances, and the compounds are collected and stored in the hind tibia with movements involving their entire legs. The fragrances stay in the pouch for a long period of time and form a complex chemical blend. The blends are species specific, and are commonly hypothesized to be used for intraspecific communication in courtship. To the right is a picture of a male Eulaema hovering around the Catasetum discolor orchid.
Wing buzzing