Megalopta

Megalopta is a widespread neotropical genus in the tribe Augochlorini in family Halictidae, known as the sweat bees.[1] They are the largest of the five nocturnal genera in Augochlorini. Most have pale integumentary pigmentation, and all have large ocelli, most likely a feature of their nocturnal behavior.[2] They live in tropical central America and the entirety of South America. The subgenus Noctoraptor is cleptoparasitic.[3] They are not known from the fossil record.[4]

Megalopta
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Halictidae
Subfamily: Halictinae
Genus: Megalopta
(Smith) 1853

Megalopta was first described by Frederick Smith in 1853.[5] The model species was Megalopta idalia, now known as Megalopta amoena.[5][6] Most studies done on Megalopta are focused on M. genalis.

General description

Megalopta are up to 2 cm long. They have large ocelli and compound eyes, used for nocturnal foraging.[7] They have a yellow/brown abdomen with dark brown banding and metallic green/yellow to bronze thorax and head.[1]

Nocturnal behavior and vision

All species of Megalopta are believed to be nocturnal or crepuscular.[4] In general, Megalopta exhibit bimodal foraging patterns and are active for about 90 minutes after the sun sets and before the sun rises,[8] regardless of food availability.[9] Males and females are active at slightly different times and the females usually have higher overall rates of activity.[8] This is hypothesized to be a niche shift to avoid competition from diurnal bees, or perhaps to avoid predation[9]

Insects generally have a pair of compound eyes accompanied by a trio of single-lensed ocelli on the top of their head.[10] While most nocturnal insects have superposition compound eyes, all hymenoptera have apposition eyes that are less sensitive to light than superposition eyes. Megalopta's apposition eyes are thirty times more sensitive to light than diurnal bees, but even this does not explain the accuracy of their vision.[11] They may use their ocelli to supplement their night vision as well. Crepuscular bees have larger ocelli than diurnal bees, and nocturnal bees have the largest ocelli of all.[12] Ocelli are not used for precise visual information, but can be used for other uses of visual information. Megalopta ocelli are highly adapted for sensitivity. They have large ocellar lenses and the percent area of the retina covered by the rhabdom is five times higher than diurnal bees.[10] However, the adaptation to sensitivity most likely came at the cost of temporal resolution. One theory is they use neural spatial summation strategies to enhance their temporal resolution.[13] Their rhabdom are elongated, with microvilli aligned in the same direction which potntially allows them to see the direction of polarized light.[10] Megalopta ocelli have a dorsal rim, where the photoreceptors are sensitive to polarized light, such as from the rising or setting sun. Sunset and sunrise create unique polarized light patterns in the sky, and Megalopta may be using these light patterns to navigate.[14] Despite having the superficial anatomy for polarized light directionality detection, the rhabdom are "worm-shaped" and arranged radially, which negates this ability.[10] Meglopta also lack pigments in their ocelli that detect short-wavelength light, perhaps a result of their jungle habitat.[10]

Nesting and the female hierarchy

Megalopta nest in dead branches, sticks, and vines. Their nests have a distinctive collar around the entrance made of chewed wood and consist of a large hollow tunnel and several cells.[4] The internal cells are made of the same chewed wood as the entrance. Megalopta are facultatively eusocial.[2] Their nests range from single female nests up to eleven female nests, but social nests usually contain 2-4 females.[15] As the dry season progresses, single female nests gradually shift into multiple female nests, a result of females hatching and remaining in the nest.[4] Usually, at least one female offspring stays in the nest and does not reproduce or grow ovaries. She instead maintains the nest and forages while the foundress continues to reproduce.[16] Eusocial communities have an overlap of generations of nest-mates, meaning that two or more broods must be laid and hatch during the mating season.[17] Eggs are usually laid during the dry season and hatch after 35 days.[4][17] Eggs laid in a drier dry season usually produce numerically more, larger individuals that are involved in reproduction, as opposed to a comparatively wet dry season, which produces fewer, smaller workers.[17] The association between reproduction and the dry season is likely a result of floral availability.[1] The benefits of solitary versus eusocial lifestyles change with the seasons. In the dry season, eusocial lifestyles provide productivity benefits while in the wet season, the benefits are typically insurance-based.[18]

In a multi-female hive, there is typically one dominant female and the rest are considered supernumerary.[17] The dominant female usually is macrocephalic and the oldest female in the hive.[3] The dominant female is analogous to the queen in honeybee hives, and can also be called the queen or the foundress. The supernumerary females fall into two roles: foragers and in-nest. The in-nest females generally stay in the nest and guard the entrance, as well as hygiene-oriented tasks.[15] Halictinae are mass-provisional, meaning they cache the food necessary for larval growth before the eggs are laid and do not interact with larvae during development.[16] However, experimentally, foundresses have displayed the ability to identify issues within a sealed cell. The foundresses opened the cell to assess the condition of the larvae and consequently either found something wrong, aborted the larvae, and reused the cell, or found nothing wrong and resealed the cell. The larvae in the resealed cells developed normally.[16] Another parental behavior performed by foundresses is hygienic-based: the removal of faeces from cells that produced healthy adults.[16] These deviations from mass-provisional behaviors are thought to be a precursor to eusociality.[16]

Gynandromorphy

Gynandromorphy is the presence of both female and male characteristics in a single organism. Two species of Megalopta have exhibited gynandromorphy: Megalopta amoena and the heavily studied Megalopta genalis. Both specimens had a bilateral split with male characteristics on the left and female characteristics on the right. In comparison to male or female individuals who have bimodal foraging periods, the gynandromorph’s activity was shifted significantly earlier in the day.[8] It is important to note that this study was based on a single specimen and generalizations about gynandromorphy in Megalopta cannot be made. Furthermore, this mutations is extremely rare, with only two specimens having been found in the entire genus.

Interactions with other species

Macrosiagon gracilis is a parasite of M. genalis and M.ecuadoria.[19] Megalopta have lower rates of brood parasitism than other solitary bees. Significant brood parasites include Lophostigma cincta, a mutilid wasp, and cleptoparasitic Megalopta species.[9] In many dead nests, slits are found in the stick and the cells are destroyed. This is thought to be the work of the silky anteater, Cyclopes didactylus, but is unconfirmed.[4] Females also often have large numbers of nematodes in their metasomal glands.[4] The larvae of a parasitic fly, Fiebrigella sp., consume the pollen stores in Megalopta cells, causing the larvae inhabiting those cells to have a smaller body size.[15] Parkia velutina is pollinated by Megalopta[7]

Cleptoparasitism

Cogener cleptoparasitism has been observed in the subgenus Noctoraptor. This means that these bees parasitize other bees in the Megalopta genus. M. byroni parasitizes M. genalis and M. ecuadoria, but most likely parasitizes other species[4]. In the case of Noctoraptor, cleptoparasitism takes the form of brood parasitism. Noctoraptor do not have the physiology to build nests or cells, making them obligate parasites that invade the nests of the other Megalopta to lay eggs.

Species and subgenera

There is considerable discourse on the phylogeny within Megalopta. One school of thought states Megalopta has two subgenera: Megalopta and Noctoraptor.[2] The subgenus Noctoraptor was described by Engel in 1997, with the type species of M. byroni.[20] M. byroni was named in memory of Byron A. Alexander, who made heavy contributions to the study of parasitic bees. M. byroni was the first known nocturnal parasitic bee.[20] Noctoraptor can be differentianted from other Megalopta by anatomical differences that are linked to parasitism, including a reduced scopa, large scythe-shaped mandibles, and the lack of a bastibial plate.[20] In newer literature, instead of being classified into the two subgenera, the divisions are made between five species groups: Aegis, Amoena, Yanomami, Byroni, and Sodalis. These groups are defined by similar physical characteristics. The byroni species groups contains the species that would be in Noctoraptor.[6] These species groups have been determined for Megalopta in Brazil, so the species group listings do not include all known species.[6] The species group system is not widely used.

Regardless of subgenera or species groups, Megalopta is most likely paraphyletic and is grouped with the genus Xenochlora, with the species M. atra being most closely related to Xenochlora over other Megalopta.[21] Xenochlora may be a subgenus of Megalopta.[21] M. atra is considered a highland species, while the rest of the genus is lowland. Megalopta, Megommation, and Megaloptidia form a single clade with a dim-light foraging ancestor. This implies that the clade Xenochlora reverted to diurnal foraging after the adaptations to nocturnal foraging evolved.[21]

The species Megalopta amoena has been known under several different names: Megalopta ecuadoria, Megalopta centralis, Megalopta idalia, Megalopta gibbosa, Megalopta ochrias, Megalopta lecointei, and Megalopta vigilans.[6]

List of species
  • Megalopta aegis (Vachal, 1904)[22]
  • Megalopta aeneicollis (Friese, 1926)[22]
  • Megalopta amoena (Spinola, 1853)[22]
  • Megalopta armata (Friese, 1926)[22]
  • Megalopta atlantica (Santos & Silveira, 2009)[22]
  • Megalopta atra (Engel, 2006)[22]
  • Megalopta boliviensis (Friese, 1926)[22]
  • Megalopta byroni (Engel, Brooks & Yanega, 1997)[22]
  • Megalopta chaperi (Vachal, 1904)[22]
  • Megalopta cuprea (Friese, 1911)[22]
  • Megalopta fornix (Vachal, 1904)[22]
  • Megalopta furunculosa (Hinojosa-Diaz & Engel, 2003)[22]
  • Megalopta genalis (Meade-Waldo, 1916)[22]
  • Megalopta guarani (Santos & Melo, 2015)[6]
  • Megalopta guimaraesi (Santos & Silveira, 2009)[22]
  • Megalopta huaoranii (Gonzalez, Griswold & Ayala, 2010)[22]
  • Megalopta karitiana (Santos & Melo, 2015)[6]
  • Megalopta lecointei (Friese, 1926)[22]
  • Megalopta mapinguari (Santos & Melo, 2015)[6]
  • Megalopta munduruku (Santos & Melo, 2015)[6]
  • Megalopta mura (Santos & Melo, 2015)[6]
  • Megalopta nigreiventris (Friese, 1926)[22]
  • Megalopta nitidicollis (Friese, 1926)[22]
  • Megalopta noctifurax (Engel, Brooks & Yanega, 1997)[22]
  • Megalopta notiocleptis (Engel, 2011)[22]
  • Megalopta opacicollis (Friese, 1926)[22]
  • Megalopta peruana (Friese, 1926)[22]
  • Megalopta piraha (Santos & Melo, 2015)[6]
  • Megalopta purpurata (Smith, 1879)[22]
  • Megalopta sodalis (Vachal, 1904)[22]
  • Megalopta sulciventris (Friese, 1926)[22]
  • Megalopta tacarunensis (Cockerell, 1923)[22]
  • Megalopta tetewana (Gonzalez, Griswold & Ayala, 2010)[22]
  • Megalopta xavante (Santos & Melo, 2015)[6]
  • Megalopta yanomami (Santos & Melo, 2015)[6]

Species groups
  • Aegis species group
    • Megalopta aegis[6]
    • Megalopta aeneicollis[6]
    • Megalopta nitidicollis[6]
    • Megalopta sulciventris[6]
  • Amoena species group
    • Megalopta amoena[6]
    • Megalopta chaperi[6]
    • Megalopta guimaraesi[6]
    • Megalopta mura[6]
  • Yanomami species group
    • Megalopta piraha[6]
    • Megalopta yanomami[6]
  • Byroni species group
    • Megalopta atlantica[6]
    • Megalopta guarani[6]
    • Megalopta xavante[6]
    • Megalopta mapinguari[6]
    • Megalopta purpurata[6]
    • Megalopta karitiana[6]
  • Sodalis species group
    • Megalopta cuprea[6]
    • Megalopta munduruku[6]
    • Megalopta sodalis[6]

References
  1. Janzen, Daniel H. (1968). "Notes on Nesting and Foraging Behavior of Megalopta (Hymenoptera: Halictidae) in Costa Rica". Journal of the Kansas Entomological Society. 41 (3): 342–350. ISSN 0022-8567. JSTOR 25083720.
  2. Engel, Michael S. (2000). "Classification of the bee tribe Augochlorini (Hymenoptera, Halictidae). Bulletin of the AMNH ; no. 250". hdl:2246/1598. Cite journal requires |journal= (help)
  3. Engel, M. S. (2006). "A new nocturnal bee of the genus Megalopta, with notes on other Central American species". Mitteilungen des Internationalen Entomologischen Vereins e V Frankfurt. 31: 37–49.
  4. WCISLO, WILLIAM T.; ARNESON, LAURA; ROESCH, KARI; GONZALEZ, VICTOR; SMITH, ADAM; FERNÁNDEZ, HERMÓGENES (2004-10-20). "The evolution of nocturnal behaviour in sweat bees, Megalopta genalis and M. ecuadoria (Hymenoptera: Halictidae): an escape from competitors and enemies?". Biological Journal of the Linnean Society. 83 (3): 377–387. doi:10.1111/j.1095-8312.2004.00399.x. ISSN 0024-4066.
  5. Smith, Frederick (1853). Catalogue of hymenopterous insects in the collection of the British museum... London: Printed by order of the Trustees. doi:10.5962/bhl.title.8766.
  6. Santos, L. M.; Melo, G. A. R. (2015-03-27). "Updating the taxonomy of the bee genus Megalopta (Hymenoptera: Apidae, Augochlorini) including revision of the Brazilian species". Journal of Natural History. 49 (11–12): 575–674. doi:10.1080/00222933.2014.946106. ISSN 0022-2933. S2CID 84687648.
  7. Hopkins, M. J. G.; Hopkins, H. C. Fortune; Sothers, C. A. (September 2000). "Nocturnal pollination of Parkia velutina by Megalopta bees in Amazonia and its possible significance in the evolution of chiropterophily". Journal of Tropical Ecology. 16 (5): 733–746. doi:10.1017/s0266467400001681. ISSN 0266-4674.
  8. Krichilsky, Erin; Vega-Hidalgo, Álvaro; Hunter, Kate; Kingwell, Callum; Ritner, Chelsey; Wcislo, William; Smith, Adam (2020-02-27). "The first gynandromorph of the Neotropical bee Megalopta amoena (Spinola, 1853) (Halictidae) with notes on its circadian rhythm". Journal of Hymenoptera Research. 75: 97–108. doi:10.3897/jhr.75.47828. ISSN 1314-2607.
  9. Smith, Adam R.; Kitchen, Shannon M.; Toney, Ryan M.; Ziegler, Christian (March 2017). "Is Nocturnal Foraging in a Tropical Bee an Escape From Interference Competition?". Journal of Insect Science. 17 (2). doi:10.1093/jisesa/iex030. ISSN 1536-2442. PMC 5469389. PMID 28931157.
  10. Berry, R. P.; Wcislo, W. T.; Warrant, E. J. (2011-03-23). "Ocellar adaptations for dim light vision in a nocturnal bee". Journal of Experimental Biology. 214 (8): 1283–1293. doi:10.1242/jeb.050427. ISSN 0022-0949. PMID 21430205. S2CID 10442933.
  11. Warrant, Eric J.; Kelber, Almut; Gislén, Anna; Greiner, Birgit; Ribi, Willi; Wcislo, William T. (2004-08-10). "Nocturnal Vision and Landmark Orientation in a Tropical Halictid Bee". Current Biology. 14 (15): 1309–1318. doi:10.1016/j.cub.2004.07.057. ISSN 0960-9822. PMID 15296747. S2CID 4980024.
  12. Kerfoot, William B. (January–February 1967). "Correlation between Ocellar Size and the Foraging Activities of Bees (Hymenoptera; Apoidea)". The American Naturalist. 101 (917): 65–70. doi:10.1086/282470. ISSN 0003-0147. S2CID 85377556.
  13. Baird, Emily; Fernandez, Diana C.; Wcislo, William T.; Warrant, Eric J. (2015). "Flight control and landing precision in the nocturnal bee Megalopta is robust to large changes in light intensity". Frontiers in Physiology. 6: 305. doi:10.3389/fphys.2015.00305. ISSN 1664-042X. PMC 4623526. PMID 26578977.
  14. Warrant, Eric J.; Kelber, Almut; Wallén, Rita; Wcislo, William T. (December 2006). "Ocellar optics in nocturnal and diurnal bees and wasps". Arthropod Structure & Development. 35 (4): 293–305. doi:10.1016/j.asd.2006.08.012. ISSN 1467-8039. PMID 18089077.
  15. Smith, Adam R.; Wcislo, William T.; O’Donnell, Sean (2008-07-03). "Body Size Shapes Caste Expression, and Cleptoparasitism Reduces Body Size in the Facultatively Eusocial Bees Megalopta (Hymenoptera: Halictidae)". Journal of Insect Behavior. 21 (5): 394–406. doi:10.1007/s10905-008-9136-1. ISSN 0892-7553. S2CID 23107308.
  16. Quiñones, A. E.; Wcislo, W. T. (2015). "Cryptic extended brood care in the facultatively eusocial sweat bee Megalopta genalis". Insectes Sociaux. 62 (3): 307–313. doi:10.1007/s00040-015-0409-3. ISSN 0020-1812. PMC 4469088. PMID 26097252.
  17. Tierney, S. M.; Fischer, C. N.; Rehan, S. M.; Kapheim, K. M.; Wcislo, W. T. (May 2013). "Frequency of social nesting in the sweat bee Megalopta genalis (Halictidae) does not vary across a rainfall gradient, despite disparity in brood production and body size". Insectes Sociaux. 60 (2): 163–172. doi:10.1007/s00040-012-0280-4. ISSN 0020-1812. S2CID 949049.
  18. Smith, A. R.; Kapheim, K. M.; Wcislo, W. T. (November 2019). "Survival and productivity benefits of sociality vary seasonally in the tropical, facultatively eusocial bee Megalopta genalis". Insectes Sociaux. 66 (4): 555–568. doi:10.1007/s00040-019-00713-z. ISSN 0020-1812. S2CID 195353744.
  19. Falin, Zachary H.; Arneson, Laura C.; Wcislo, William T. (2000). "Night-Flying Sweat Bees Megalopta genalis and Me. ecuadoria (Hymenoptera: Halictidae) as Hosts of the Parasitoid Beetle Macrosiagon gracilis (Coleoptera: Rhipiphoridae)". Journal of the Kansas Entomological Society. 73 (3): 183–185. ISSN 0022-8567. JSTOR 25085964.
  20. Engel, Michael S.; Brooks, Robert W.; Yanega, Douglas (1997). New genera and subgenera of augochlorine bees (Hymenoptera: Halictidae) / by Michael S. Engel, Robert W. Brooks, and Douglas Yanega. Lawrence, Kan.: Natural History Museum, The University of Kansas. doi:10.5962/bhl.title.4042.
  21. Tierney, Simon M.; Sanjur, Oris; Grajales, Grethel G.; Santos, Leandro M.; Bermingham, Eldredge; Wcislo, William T. (2011-07-27). "Photic niche invasions: phylogenetic history of the dim-light foraging augochlorine bees (Halictidae)". Proceedings of the Royal Society B: Biological Sciences. 279 (1729): 794–803. doi:10.1098/rspb.2011.1355. ISSN 0962-8452. PMC 3248740. PMID 21795273.
  22. "Moure's Bee Catalogue". moure.cria.org.br. Retrieved 2020-11-13.
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