Nest cells of Leafcutter Bees from the Rancho La Brea Tar Pits.

Leafcutter Bees (Megachilidae) cut their name from their habit of cutting disk-shaped segments from leaves, from which they build their nests. Each female Bee digs, tunnels, or co-opts a burrow in soft soil or plant material, within which several small nests cells, each comprising an egg and a supply of food wrapped in a parcel made from leaf material, are deposited. The oldest traces of this activity, fossil leaves with cutouts thought highly likely to come from Leafcutter Bee activity, date from the Early-to-Middle Eocene of Europe and North America.

In a paper published in the journal PLoS One on 9 April 2014, Anna Holden of the Entomology Section at the Natural History Museum of Los Angeles County, Jonathan Koch of the Department of Biology and Ecology Center at Utah State University, Terry Griswold of the USDA-ARS Pollinating Insect Research Unit at Utah State University, Diane Erwin of the Museum of Paleontology at the University of California, Berkeley and Justin Hall of the Dinosaur Institute at the Natural History Museum of Los Angeles County, discuss the discovery of two Leafcutter Bee nest cells from the Rancho La Brea Tar Pits in Los Angeles County, California.

The nest cells come from Pit 91 at Rancho La Brea, and are thought to be between 23 000 and 40 000 years old, and thought likely to belong to the extant species Megachile gentilis. Each is cylindrical, about 10.5 mm in length and 4.9 mm in diameter.

(A) Nest cell containing male pupa showing cylindrical shape, tapered, rounded bottom at left typical of the first constructed cell, and remains of oblong leaf disc with Type 1 venation. (B) Bottom of first constructed cell (containing male pupa) with possible portion of bottom circular leaf disk visible and outlined with arrows. (C) Cap of nest cell containing male pupa. (D) Nest cell containing female pupa. Arrow shows margin of oblong leaf disc with Type 2 venation. (E) Circular, bottom disc of nest cell (containing female pupa). In life, this end abutted the anterior end of the next cell. (F) Cap of nest cell containing female pupa. (G) Nest cell of female pupa showing oblong side wall leaf cutout which does not reach bottom of cell and is instead supported by circular bottom disc. (H) Remains of oblong leaf disc with relatively smooth-cut margins and Type 3 venation. (I) View showing five overlapping oblong disks (1–5) comprising the sidewalls and circular bottom discs. (J) Nest cell containing female pupa showing Type 4 venation on upper, right corner. (K) Nest cell of modern Megachile gentilis, showing circular disc bottom and oblong, sidewall leaf. Holden et al. (2014).

Micro-CT scans of the cells revealed the presence of two immature Bees, one male and one female, apparently preserved when pupating. The pupae of Leafcutter Bees probably have better preservational potential than other stages, due to the tough secretions produced by the larva prior to pupating, which from a hard protective case around the insect during this vulnerable period.

Micro-CT scans of the male pupa and its position within the nest cell. (A) Dorsal view of pupa within nest. (B) Dorsal view of pupa. (C) Lateral view of pupa within nest. (D) Lateral view of pupa. (E) Cross-section of nest and pupae. (F) Ventral view of pupa. Holden et al. (2014).

Megachile gentilis is today found in California and southwest Arizona, in dry areas where the temperature seldom falls below 0°C. The temperature in the area where the nests were found is likely to have varied considerably between 23 000 and 40 000 years ago, though all tar pit fossils are, by their nature, likely to have been laid down in warmer periods (tar pits are formed when crude oil deposits become exposed at the surface, when this happens in a warm climate the lighter fractions evaporate leaving a thick tar in which animals can become trapped and preserved). 

Micro-CT scans of the female pupa and its position within the nest cell. (A) Dorsal view of pupa within nest. (B) Dorsal view of pupa. (C) Lateral view of pupa within nest. (D) Lateral view of pupa. (E) Cross-section of nest and pupae. (F) Ventral view of pupa. Holden et al. (2014).

See also…

 Two new species of Orchid Bee from Columbia and Brazil.

The Orchid Bees (Euglossini) of Central and South America have an unusual relationship with the Orchids they pollenate, in that the Orchids do not produce a food substance with which to attract the Bees, but rather a variety of aromatic chemicals used by the males Bees to attract a mate. Each male must visit a number of flowers in order to collect enough...

 A new species of Leafcutter Bee from Mexico.

Leafcutter Bees (Megachilidae) get their name from their habit of cutting segments from leaves with which to line their nests. They are solitary Bees, each female Bee building her own nest in a wood...

 The diversification of Bees.

Bees (Anthophila) are generally accepted to have arisen during the Mesozoic, but estimates of exactly when vary considerably. The group are not well known in the fossil record (at least in part because many early palaeontologists tended to ignore Insect fossils in Mesozoic beds, happily destroying them in the quest for Dinosaurs and other large, glamorous Vertebrates), with the earliest putative Bee being Melittosphex burmensis...

Follow Sciency Thoughts on Facebook.

Two new species of Orchid Bee from Columbia and Brazil.

The Orchid Bees (Euglossini) of Central and South America have an unusual relationship with the Orchids they pollenate, in that the Orchids do not produce a food substance with which to attract the Bees, but rather a variety of aromatic chemicals used by the males Bees to attract a mate. Each male must visit a number of flowers in order to collect enough compound to attract a female, and in doing so spreads pollen from flower to flower. The discovery of this trait in the 1960s led to the realization that male Bees could be attracted by using appropriate aromatic chemicals, and, since male Euglossid Bees are brightly coloured and easily distinguished, the subsequent identification and description of a large number of Bee species from male specimens only.

In a paper published in the journal ZooKeys on 13 September 2012, Ismael Hinojosa-Díaz of the Division of Entomology at the Natural History Museum and Department of Ecology & Evolutionary Biology of the University of Kansas, and the Department of Environmental Studies at Emory University, André Nemésio of the Instituto de Biologia at the Universidade Federal de Uberlândia, and Michael Engel, also of the Division of Entomology at the Natural History Museum and Department of Ecology & Evolutionary Biology of the University of Kansas, describe two new species of Orchid Bees from Columbia and Brazil, both of which are placed in the genus Euglossa.

The first new species described is named Euglossa embera, in reference to the Emberá, an indigenous people occupying the Pacific lowlands of Columbia. The species is described from four male and one female specimens, collected in February 1977 by the Rio Anchicaya in Valle del Cauca Department on the Pacific Coast of Columbia, and stored in the entomological collections of the University of Kansas Natural History Museum and the Universidade Federal de Minas Gerais. These specimens were labelled as belonging to Euglossa bursigera, a Central American species from which it is morphologically distinct. The only known female of Euglossa embera is 9.56 mm in length, the males range from 11.33 mm to 12.02 mm. Both sexes are a metallic blue-green with a golden-bronzy iridescence.

Euglossa bursigera. (1) Male in dorsal view. (2) Male in lateral view. (3) Female in dorsal view. (4) Female in lateral view. Hinojosa-Díaz et al. (2012).

The second new species is named Euglossa adiastola, meaning ‘confused’ or ‘not separated’ due to confusion between this species and Euglossa augaspis, an Amazonian species from which it can be differentiated on the basis of its mouthparts; its mid-mandibular tooth being well differentiated from its outer tooth. The species is described from 16 specimens, all male, collected by André Nemésio from the coastal Northern Atlantic forests of Brazil. Euglossa adiastola is a 12.81 mm bottle green Euglossid Bee with a golden-bronzy hue.

Euglossa adiastola. (21) Male specimen in dorsal view. (22) Male specimen in lateral view. Hinojosa-Díaz et al. (2012).

See also…

 A new species of Leafcutter Bee from Mexico.

Leafcutter Bees (Megachilidae) get their name from their habit of cutting segments from leaves with which to line their nests. They are...


 The diversification of Bees.

Bees (Anthophila) are generally accepted to have arisen during the Mesozoic, but estimates of exactly when vary considerably. The group are not well known in the fossil record (at least in part because many early palaeontologists tended to ignore Insect fossils in Mesozoic beds, happily destroying them in the quest for Dinosaurs and other large, glamorous Vertebrates), with the earliest putative Bee...




 A Stingless Bee from Colombian copal.

The film Jurassic Park is based upon the idea that it might be possible to recover the DNA of Dinosaurs from inside Mosquitoes preserved in amber (fossilized tree resin). However attempts to recover biological material from amber have generally ended in failure, leaving most palaeobiologists to conclude that this is in fact impossible, and that organisms are effectively preserved in amber only as images.

Follow Sciency Thoughts on Facebook.

A new species of Leafcutter Bee from Mexico.

Leafcutter Bees (Megachilidae) get their name from their habit of cutting segments from leaves with which to line their nests. They are solitary Bees, each female Bee building her own nest in a wood cavity, plant stem or the ground, in which several young are raised in separate cells. The cells are each provided with their own food source of nectar before being sealed. Typically the female young are placed in larger cells with more food, further inside the nest, as adult females are larger and take longer to mature. The sex of the adult Bee appears to be determined by the size of its cell and the amount of food it was provided with as a larva.

In a paper published in the journal ZooKeys on 13 September 2012, Emily Bzdyk of the Bohart Museum of Entomology at the University of California, Davis, describes a new species of Leafcutter Bee from Mexico, as part of a wider study of North American Leafcutter Bees.

The new species is placed in the genus Megachile, and given the specific name pankus, which Bzdyk describes as a ‘nonsense combination’. Megachile pankus is described from five female specimens from Hidalgo and Sonora States in Mexico between 1935 and 1991 and stored in the entomological collections of the Bee Biology and Systematics Lab in Logan, Utah, the American Museum of Natural History in New York and the Bohart Museum of Entomology. The males of the species are unknown. Megachile pankus is differentiated from all closely related species by the arrangement of teeth on its mouthparts. It is a 10 mm black Leafcutter Bee with white hairs and brown tinted wings.

Illustration of Megachile pankus in dorsal view. Bzdyk (2012).

 

Photographs of Megachile pankus: (A) Lateral view. (B) Dorsal view. (C). Mandible showing angulation. Bzdyk (2012).

Megachile pankus belongs to a group of Bees mostly distributed in more northerly climates (southern US to southern Canada); while it has several relatives that are also found in Mexico it appears to be unique in its exclusively Mexican distribution. There are records of it being seen visiting only one flower, a species of Petalostemon, a type of Legume.

The known distribution of Megachile pankus. Bzdyk (2012).

See also…

 The diversification of Bees.

Bees (Anthophila) are generally accepted to have arisen during the Mesozoic, but estimates of exactly when vary considerably. The group are not well known in the fossil record (at least in part because many early palaeontologists tended to ignore Insect fossils in Mesozoic beds, happily destroying them in the quest for Dinosaurs and other large, glamorous Vertebrates), with the earliest putative Bee being Melittosphex burmensis, from 100-110 million-year-old Burmese Amber, which some...

 A Stingless Bee from Colombian copal.

The film Jurassic Park is based upon the idea that it might be possible to recover the DNA of Dinosaurs from inside Mosquitoes preserved in amber (fossilized tree resin). However attempts to recover biological material from amber have generally ended in failure, leaving most palaeobiologists to conclude that this is in fact impossible, and that organisms are effectively preserved in amber only as images. 

 A new species of Oil Bee from northeast Brazil.

Oil Bees (Centridini) are largish Bees with special combs of bristles or velvety pads on their legs and abdomens, which they use to gather floral oils instead of or as well as nectar and pollen. They are mostly found in the Neotropics.

Follow Sciency Thoughts on Facebook.

The diversification of Bees.

Bees (Anthophila) are generally accepted to have arisen during the Mesozoic, but estimates of exactly when vary considerably. The group are not well known in the fossil record (at least in part because many early palaeontologists tended to ignore Insect fossils in Mesozoic beds, happily destroying them in the quest for Dinosaurs and other large, glamorous Vertebrates), with the earliest putative Bee being Melittosphex burmensis, from 100-110 million-year-old Burmese Amber, which some palaeoentomologists  argue is a Crabronid Wasp (the group of Wasps most closely related to Bees), while the oldest universally accepted Bee is Cretotrigona prisca, a 65-million-year-old probable Stingless Bee from New Jersey Amber. Attempts to date the origin of the group using genetic molecular dating techniques have, to date, been equally problematic, with origin dates varying from 275 million years ago (early Permian) to 147 million years ago (Late Jurassic).

An artists impression of Cretotrigona prisca, from the Late Cretaceous, the oldest universally accepted Bee. Michael Rothman in Engel (2000).

This lack of knowledge about the timing of the origin and diversification of Bees presents difficulties for palaeoecologists trying to understand Cretaceous ecosystems. Between 78% and 94% of all modern Flowering Plants (Angiosperms) are pollinated by Animals, with Bees being one of the most important groups. The exact date of origin for the Angiosperms is equally obscure, but the group is known to have existed by the Early Cretaceous and undergone a dramatic radiation during the middle part of the period, so that Late Cretaceous floras are dominated by Flowering Plants. Logically it would be expected that such an outburst of diversity and ecological success would be accompanied by a similar rise in some associated group of pollinators, with Bees being the primary candidate, but to date evidence for this has been lacking.

In a paper published in the Proceedings of the Royal Society: Series B Biological Sciences on 30 January 2013, Sophie Cardinal of the Canadian National Collection of Insects at Agriculture and Agri-Food Canada and Bryan Danforth of the Department of Entomology at Cornell University, publish the results of a new genetic study of the phylogeny of Bees, which examines seven different gene groups and uses a relaxed molecular clock to calibrate this phylogeny from the fossil record (this assumes that any group must have originated before its first occurrence in the fossil record). Since Melittosphex burmensis is not universally accepted as a Bee it was not used in the study, and since Cretotrigona prisca is not universally accepted as a member of the modern Meliponini (Stingless Bees) it is treated only as a Bee, not a Stingless Bee.

Cardinal & Danforth produced a dated molecular phylogeny which suggested that the Bees arose in the Early Cretaceous, around 140 million years ago, and differentiated into the modern Bee groups (except the Leaf-cutter Bees, Megachilini) during the Middle Cretaceous, with a latest common ancestor of all modern bees living between 113 and 132 million years ago. This supports the idea that Bees underwent a major evolutionary radiation at the same time as Flowering Plants, and that the diversification of both groups was driven by the plant/pollinator relationship.

Time calibrated phylogeny of bees based on analysis 3 (age of the root node sampled from a normal distribution with a mean of 140 and a s.d. of five and tree constrained to have the same relationships as the MRBAYES produced tree at the subfamily and taxonomically higher levels). Horizontal bars indicate 95% HPD of estimated divergence times. Posterior probabilities are shown at the right of each node. Cardinal & Danforth (2013).

Cardinal & Danforth did not include trace fossils in their calculations, nevertheless they do observe that their results do confirm the existence of Halictid Bees by the Late Cenomanian, when putative burrows made by the group have been found in Arizona. Conversely their results suggest that the last common ancestor of all modern Leaf-cutter Bees (Megachilini) lived more recently than the Mid-Eocene Messel Shale, where putative damage to leaves caused by members of this group has been found. Cardinal and Danforth suggest that this does not rule out a Leaf-cutter Bee as the cause of this damage, as the group could potentially have existed before the last common ancestor of all its modern members.

See also…

 A Stingless Bee from Colombian copal.

 A new species of Oil Bee from northeast Brazil.

 A new species of Solitary Bee from Peru.

Follow Sciency Thoughts on Facebook.