Megachile (Aethomegachile) laticeps, Smith 1853
|Figure 1. Leaf damage caused by a leaf-cutter bee, which uses leaves to build a nest (images not to scale). Leaf image by Sebastian Ow; bee image from Ascher et al. (2016) ; nest image by Eunice Soh ; all images used with permission.|
Cut leaves are common wherever you look, and the first thought that comes to your mind might be that they are caused by grasshoppers or caterpillars. However, not all cuts are as typical as they seem - they could be caused by leaf-cutter bees!
What is a Leaf-cutter Bee?
The name Leaf-cutter Bee, when put together, may seem strange at first. After all, what do bees have anything to do with leaves? Let us break down the different components of its name to find out more!
|Leaves are not necessarily only used for food. In the case of the leaf-cutter bee, leaves are used in nest-building.||How do leaf-cutter bees cut leaves? The 'cutter' in their names comes from the apparatus these bees have on their bodies to cut leaves. Leaf-cutter bees have mandibles (mouthparts) with cutting edges, something unique to this group of bees .||Leaf-cutter bees belong to the family Megachillidae and genus Megachile, constituting a morphologically and behaviourally diverse group . There are more than 1525 described species of Megachile species worldwide, making it one of the most hyperdiverse bee genera .|
If you are intrigued by this group of bees and wondering why they are so different from the bee you used to know, our most familiar image of a bee (Western Honey Bee - top hit in Google when you search 'bee') gives you a guide on what to check out on this page!
Why cut leaves?
The nesting biology of leaf-cutter bees is one of the most fascinating aspects of its behaviour. Provisions in nests have to be protected from spoilage from fungus , and at the same time, there is also a need to defend larvae from predation and parasitism . The solution to these problems is thus to line brood cells in pre-existing cavities with hydrophobic material to prevent provision spoilage and minimise predation risk .
While many bees secrete a hydrophobic lining, through the Dufour’s gland, to coat the interior of the brood cells , Megachilid bees use a wide variety of materials to line their cells, such as mud, cement, petals or leaves (intact or chewed) . These foreign materials used by megachilids are hydrophobic and contain secondary compounds that have antimicrobial properties . This special adaptation of using of foreign materials in nest building may have allowed Megachilids to diversify and expand their ranges within the family . In particular, certain subgenera of Megachile, including Aethomegachile which M. laticeps belongs to, cut intact leaf pieces for use in nest-building . Some examples Megachilid nests are shown below.
|Figure 6. M. atrata nest at the side of a lobster mound, using cut leaf pieces. Image by Eunice Soh , used with permission.|
|Figure 7. M. fulvipennis nesting in a cavity in a wooden bench, lined with resin and pieces of wood. Image by Eunice Soh , used with permission.|
Leaf-cutting in action
How do leaf-cutter bees obtain their material for nest-building? Watch a leaf-cutter bee in action as it uses its mandibles to chew a circular piece out of a leaf.
Moreover, there is an art to leaf-cutting by these bees! Typically, leaf pieces used to construct cell walls and bases are oblong, while cell closures are circular . Notice how they typically begin cutting from leaf margins, and do not begin cutting from previous damage despite sufficient leaf width . While herbivory damage on leaves are common, cuts on leaves caused by leaf-cutter bees can be differentiated from those caused by other insects from their unique circular shape.
|Figure 8. Examples of leaves cut by Megachile spp. Oblong cuts are pointed out in red arrows while circular cuts are pointed out in yellow arrows. Images by Sebastian Ow, used with permission.|
Megachile are able to utilise a wide range of leaf resources in building their nests, where field observations of cut leaves in one study in Singapore found at least 48 species of plants from 17 families . In India, one study found that the bees collected leaves from 59 species of plants from 25 families . These bees do not seem to be picky about leaf sizes, morphotypes and plant habits .
|Figure 9. Percentage of plants by family used as resources for nest-building by Megachile in Singapore. Image by Eunice Soh , used with permission.|
Although leaf species collected varied significantly across Megachile species, there was no preference for native or exotic plant species . In fact, the abundance of exotic plant species in urban environments could provide a greater diversity of nest material for leaf-cutter bees .
Building a home
After obtaining their building materials, how are they used in nest-building? Check out this video of a leaf-cutter bee building its nest!
Nest of Megachile laticeps
Trap-nesting using bamboo internodes in Singapore revealed the nest biomics of M. laticeps. Individual cells are aligned linearly, with each wrapped in leaves and one outer layer of interlocking leaves between cells . Nests are sealed with circular leaf pieces .
|Figure 10. Complete nest of M. laticeps (5 cells); circular cell caps are shown on the right. Images by Eunice Soh , used with permission.|
|Figure 11. Structure of a single cell (A, B, C) and leaf pieces taken apart from one cell (D). Image by Eunice Soh , used with permission.|
|Figure 12. Post-defecating larvae of M. laticeps. Image by Eunice Soh , used with permission.|
Who else is home?
Coelioxys (Callosarissa) confusa was found to be a kleptoparasite of Megachile laticeps, stealing food that M. laticeps has collected by laying its own eggs in M. laticep’s nest .
|Figure 13. Coelioxys confusa. Image by Chui Shao Xiong, property of NUS Insect Diversity Lab, used with permission.|
|Figure 14. Other organisms found in nest of M. laticeps: microlepidoptera larva (A), tachinid fly (B), Images by Eunice Soh , used with permission.|
Bringing food home
Megachilids transport pollen in a unique way – through hairs called scopae located on their bellies, under their abdomen (metasoma) ! This feature is unique to Megachilidae and can be used to distinguish them from other bee families. On the other hand, honeybees and bumblebees carry pollen in baskets known as corbiculae, which are made of dense hairs woven together to form a concave shape . Many other bees do not have pollen baskets, but specialised long or sticky hairs called scopae on their legs .
|Metasoma||Pollen basket||Scopae on leg|
|Leaf-cutter bee (M. laticeps) collecting pollen. Check out the pollen on scopae under the abdomen!||Asian honeybee (Apis cerana) collecting pollen with a pollen basket.||True long-horned bee (Melissodes trinodis) with long hairs on its hind leg that allow it to carry pollen.|
The table below summarises the modes of pollen transport by different families of bees, where Megachilidae almost exclusively transports pollen through the metasoma.
|Figure 18. Table showing different modes of pollen transport, where Megachilidae almost exclusively uses metasoma for pollen transport. Table from Roubik, 1989 , fair use.|
Like most Megachile in Singapore, Megachile laticeps is polylectic, meaning that it is non-specialist in collecting pollen from different plant groups . M. laticeps has been observed collecting pollen from Crotalaria pallida, Peltophorum pterocarpum (Fabaceae), Memecylon caeruleum (Melastomataceae), and Vitex trifolia (Lamiaceae) .
The diversity in external morphology among Megachile species is stunning, a far cry from the typical black-and-yellow honeybee we imagine when we think of bees! Just check out some of the Megachile that can be found in Singapore:
|Figure 21. Some Megachile species found in Singapore. Images from Ascher et al. (2016) , used with permission.|
1. Black-and-orange metasoma
2. Black-and-white metasoma
3. Black habitus with orange wings
Megachile laticeps belongs to the first group, which is characterised by orange hairs on the head, thorax and anterior metasoma and pale apical bands on the tergum .
|Figure 22. Image by Chui Shao Xiong, property of NUS Insect Diversity Lab, used with permission (with annotations added).|
|Species||Megachile (Aethomegachile) laticeps||Megachile (Callomegachile) umbripennis||Megachile (Aethomegachile) conjuncta|
|Size (Total length in mm)||♀: 11.8; ♂: 7.4-10.2||♀: 8.4-10.7; ♂: 7.2-8.8|
M. umbripennis is noticeably smaller in size compared to the 2 other species.
|♀: 11.9; ♂: 9.2|
|Males of M. laticeps and M. conjuncta can be told apart by their genitalia morphology, where the diagnostic features are pointed out in black arrows.|
Megachile laticeps is one of the most widespread Megachile species in recent surveys of bees in Singapore . Historically, it was first sampled in Singapore in 1977, and it is presumed to be a native species . This is unlike other common species in recent years such as M. disjuncta, which was only first sampled in Singapore in 2010, suggesting that it may have been introduced locally from the dryer regions of Southeast Asia rather than being a true Singaporean native .
Megachile species in Singapore display differing habitat associations between species, with some only occurring in primary and secondary forests such as M. borneana and M. ornata . On the other hand, M. laticeps occupies truly urban habitats on top of forest edges, parks and gardens . M. laticeps is known to occur in all habitat types in Singapore except freshwater swamp forests .
|Figure 24. Distribution of M. laticeps in Singapore. Image from Ascher et al., 2016 , used with permission.|
What’s in a name?
The genus name Megachile is derived from the Greek word mega meaning ‘large’ and cheil meaning ‘lips’, with reference to the mouthparts of the leafcutter bees . On the other hand, the species name laticeps means wide-headed, derived from the Latin, where latus means ‘broad’ and suffix ceps means ‘head’ . This is why Megachile laticeps is also less commonly known as the Broad-headed Leaf-cutter Bee .
|Figure 25. Frontal and top view of M. laticeps. Images by Chui Shao Xiong, used with permission (with annotations added).|
Synonyms exist when different names are given to the same species, usually as a result of a scientist mistakenly describing a specimen as a new species when the same species has already been previously described. However, since Megachile laticeps is the first published name given to the species, it is recognised as the senior synonym and is the currently accepted name for the species.
Below is a list of synonyms of Megachile laticeps :
Megachile cinyras Cameron, 1902
Megachile otriades Cameron, 1902
Megachile caecina Cameron, 1903
Megachile gadara Cameron, 1903
Megachile robbii Ashmead, 1904
Megachile semperi Friese, 1905
Megachile varidens Cameron, 1905
Megachile roepkei Friese, 1914
Megachile metallescens Cockerell, 1918
Megachile mcgregori Cockerell, 1918
Megachile penangensis Cockerell, 1918
Megachile subignita Cockerell, 1918
Megachile laticeps Smith, 1853
First described by Frederick Smith in 1853 from a specimen in the Philippines Islands, the type specimen is kept in the British Museum (Natural History), Department of Zoology .
|Figure 26. Screenshot of original species description. Taken from Smith, 1853 , fair use.|
Genus: Megachile Latreille, 1802
Species: Megachile laticeps Smith, 1853
The subgenus Aethomegachile was first named and described in 2006 by Engel and Baker . In a recent treatment, Ascher et al. (2016) placed M. laticeps in this subgenus .
Phylogenetic relationships within many large bee clades are poorly understood. Traditionally, Megachilidae has been divided into two morphologically and behaviourally unique subfamilies, namely Fideliinae and Megachilinae . One of the first attempts to construct phylogenetic relationships between lineages of Megachilidae using molecular markers was conducted by Litman et al. in 2011 . In the study, four protein-coding genes and one ribosomal gene were sequenced and phylogenetic analyses were performed using maximum-likelihood and Bayesian methods.
The monophyly of the family Megachilidae was confirmed; however, the tribes Fideliini and Osmiini were found to be paraphyletic. The tribe Megachilini (in red in the tree below), which Megachile belongs to, was found to be a monophyletic group with a maximum-likelihood bootstrap value of 100.
|Figure 27. Fossil-calibrated maximum clade credibility tree for bee family Megachilidae. Taken from Litman et al., 2011 , fair use|
|Figure 28. Strict consensus tree showing relationships within the genus Megachile. Taken from Gonzalez et al., 2012 , fair use.|
Recently, Trunz et al. (2016) attempted to resolve relationships within the tribe Megachilini, in particular between the subgenera of the genus Megachile . Using mitochondrial DNA barcodes together with nuclear phylogeny, a matrix was created and analysed using maximum-likelihood and Bayesian inferences . All subgenera appear monophyletic and majority have high statistical support . The position of M. laticeps is marked out in a red star in the tree below. The recent placement of M. laticeps in the new subgenus Aethomegachile by Ascher et al. (2016) was confirmed by this study, where M. laticeps clustered with other species, such as M. conjuncta, placed in this subgenus .
The results of this study suggest that while relationships within subgenera are well-supported, classification between the three groups of subgenera are more challenging to resolve (see next section on groupings of subgenera). In particular, morphology-based classification proposals to divide Group 2 subgenera into genera were not supported. This suggests that there still exists disagreement on the above-species level classification of Megachile.
|Figure 29. Combined nuclear + barcode analysis for Megachilini. Taken from Trunz et al., 2016 , fair use.|
Ranks above species level
For ranks to be useful, they should reflect equivalence of groups on the tree of life, such as by reflecting hierarchy, age of clade, species diversity or morphological or genetic diversity. From the fossil-calibrated tree (Figure 27), we can observe that the subfamilies and tribes of Megachilidae are dissimilar with regard to age of clade, as evidenced by the emergence of the nodes at different time periods. Among subfamilies, Pararhophitinae and Lithurginae include only one tribe each, while Megachilinae is highly diverse and contains four species-rich tribes , suggesting that subfamilies do not reflect equivalence in species diversity either.
Furthermore, the division of genera and subgenera also appear to be arbitrary and unresolved. While most authors originally recognised several subgenera, they had placed bees in the genus Megachile in a single genus, until Michener (1962) recognised the great differences between the subgenera and divided the genus into 3 genera . Some authors consider Group 1, 2 and 3 to correspond to the genera Megachile, Chalicodoma and Creightonella , while others have proposed to divide some groups into multiple genera .
However, in an updated version of his book The Bees of the World, Michener (2007) acknowledged the presence of intermediates, where there were species that were as different as genera among other bees . He then placed subgenera of Megachile into three different groups (see table below), refraining from recognising distinct genera due to similarities in morphology across groups. Most leafcutters belong to Group 1, where Aethomegachile belongs, although it is absent in the table due to it being a relatively new genus at that point in time.
|Figure 30. Table showing groups of subgenera of Megachile. Taken from Michener, 2007 , fair use.|
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This page was authored by Angela Chan An Qi
Last curated in 2017