The Alfalfa Leafcutter Bee, Megachile (Eutricharaea) rotundata (Fabricius), is one of the most studied solitary bees in the world.  Although its nesting biology is well documented, it has not yet been reported nesting in cavities that expose the nests to open environments.  Reported here for the first time is evidence of this species nesting in an unusual manner which would subject the natal cells to exposure and increased parasite attack

Sheffield, Cory Silas

The University of Kansas: Journals@KU

Journal of MelittologyBee Biology, Ecology, Evolution, & Systematics The latest buzz in bee biologyNo. 69, pp. 1–6 1 May 2017Copyright © C.S. Sheffield.Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0).ISSN 2325-4467Unusual nesting behavior in Megachile (Eutricharaea) rotundata (Hymenoptera: Megachilidae)Cory S. Sheffield1Abstract.  The Alfalfa Leafcutter Bee, Megachile (Eutricharaea) rotundata (Fabricius), is one of the most studied solitary bees in the world.  Although its nesting biology is well documented, it has not yet been reported nesting in cavities that expose the nests to open environments.  Reported here for the first time is evidence of this species nesting in an unusual manner which would subject the natal cells to exposure and increased parasite attack.1 Royal Saskatchewan Museum, 2340 Albert Street, Regina, SK S4P 2V7, Canada (cory.sheffield@gov.sk.ca).doi: http://dx.doi.org/10.17161/jom.v0i69.6532Bees of the genus Megachile Latreille s.l. (Hymenoptera: Megachilidae) are com-monly called leafcutters as females of most species cut circular leaf pieces, less com-monly flower petals (e.g., Orr et al., 2015), or combinations of materials (e.g., Zillikens & Steiner, 2004) that are used in the construction of individual natal cells (Fig. 1), each of which will contain one developing bee.  Other species of Megachile are masons or daubers, creating nest partitions out of plant resins or similar pliable materials (Mi-chener, 2007; MacIvor & Moore, 2013).  Leafcutter bees will construct nests in a variety of places, including cavities excavated into the soil (Eickwort et al., 1981) or decom-posing wood (Hobbs & Lilly, 1954; Stephen, 1956), but most species nest in natural pre-existing cavities in wood, stone, or other substrates; see Sheffield et al. (2011) for a summary of nesting sites used by species occurring in Canada.  Regardless of the nest-ing substrate used, female leafcutter bees normally exhibit the behavior of building and provisioning their nests in a linear series, with eggs destined to become females being laid first (i.e., at the rear of the rear of the series in the nesting cavity), with males being produced towards the nest entrance.  Male post-diapause development is faster than for females (Sheffield, 2008), allowing them to exit the nesting cavity before their sisters.  An interesting exception was noted by Packer (1987) who reported on exposed single-celled nests of Megachile pseudobrevis Mitchell in apical tufts of grass in Florida.BRIEF COMMUNICATIONJournal of Melittology2 No. 69Many of the species of Megachile that nest in pre-existing cavities will utilize arti-ficial nesting substrates (e.g., Fye, 1965; Krombein, 1967; Stephen & Every, 1970; Shef-field et al., 2008, MacIvor & Packer, 2015; MacIvor, in press), popularly called bee con-dos or hotels (e.g., Ravoet et al., 2014; MacIvor & Packer, 2015; Fortel et al., 2016), or trap/cavity nests (e.g., Koerber & Medler, 1958; Medler & Koerber, 1958; Krombein, 1967; O’Neil & O’Neil, 2016; MacIvor, in press).  In these artificial nesting sites, the nesting cavities are typically pre-constructed to run horizontally and perpendicular to the nest front surface, though this arrangement may not always be available in natural cavities.  The diameter of the individual tunnels can vary to support occupant diver-sity (e.g., Tscharntke et al., 1998; Sheffield et al., 2008), and influence sex-ratio for target species (e.g., Stephen & Osgood, 1965).The use of artificial nesting sites for cavity nesting bees has greatly enhanced our knowledge of the biology of many species, including the economically important Al-falfa Leafcutter Bee, M. (Eutricharaea) rotundata (Fabricius) (Pitts-Singer & Cane, 2011). This species is not native to North America, but is commercially very important for the pollination services it provides to several crops, including alfalfa, canola, and low-bush blueberry (Richards, 1984; Sheffield, 2008; Pitts-Singer & Cane, 2011).  One of the key life history traits promoting the successful management of M. rotundata is that it will nest in large aggregations containing 1000s of individuals.  For commercial pol-lination, nesting populations are provided with artificial nesting substrates (Stephen, 1961), usually created with polystyrene (Richards, 1978) placed within a shelter.  As this species has become established throughout most of southern Canada (Sheffield et al., 2011), it will still use a range of natural and artificial pre-existing cavities (Sheffield et al., 2008), and will often be one of the most numerous nest occupants where it has established (MacIvor & Packer, 2015).Reported here for the first time is evidence that M. rotundata may be more flex-ible in its choice of nesting substrates and nesting behavior than previously thought. While visiting the Creston Museum in Creston, British Columbia, I observed and pho-Figure 1.  A natal cell of the Alfalfa Leafcutter Bee, Megachile rotundata (Fabricius) (Megachilidae) constructed with many individual leaf pieces.  The apical (i.e., flat end to the left) is where the bee’s head is, and is the direction of exiting from the cell.Sheffield: Unusual nesting of Megachile rotundata2017 3tographed (with an iPhone 5s™) a nesting population of M. rotundata building nests in the radiator of an antique Caterpillar™ farm tractor that was on display (Figs. 2–5). Nests were constructed in the typical linear fashion within these pre-existing cavities, each running parallel with the surface of the radiator (Fig. 3).  Unusual was the fact that nest construction was done with approximately half of the lateral surface of each natal cell exposed to the external environment (e.g., light, temperature/sunlight, rain), and likely parasites.  One of several such parasites is the chalcid wasp Pteromalus apum Retzius (=Pteromalus venustus Walker), a very important pest in commercial operations rearing M. rotundata populations (Hobbs & Krunic, 1971).  Adult wasps emerge and re-infect the un-emerged hosts during incubation, which are still in their cocoons but loose in large rearing containers (i.e., within a 21 day period).  If unchecked, the para-sites of M. rotundata have the ability to quickly reduce the population of bees available for pollination, so various methods of pest control are used (Eves, 1970). The conditions observed in commercial rearing facilities are seldom observed in nature, as almost all cavity-nesting bee species will utilize pre-existing cavities that are linear and of a small diameter, with only the apical end of the outermost cell being exposed at any given time.  However, the nesting behavior observed in Creston would make these bees more susceptible to parasite attack throughout nest construction as a large area of each cell was exposed.  In a study of nesting in the subgenus Moureapis Figures 2–5.  Nesting location of a population of Megachile rotundata (Fabricius) (Megachilidae) in the radiator of a Caterpillar™ tractor.  2. Entire radiator surface.  3. Section of radiator show-ing many linear series of natal cells.  4. A female constructing a natal cell with a leaf piece.  5. The likely emergence hole from previous generation; note the emergence hole is on the lateral surface of the cell, not the apical end.Journal of Melittology4 No. 69Raw, which tend to prefer to nest in much wider cavities, a number of the linear series of nests in each cavity had high numbers of hymenopteran and dipteran parasites, and psocopteran nest associates (Cardoso & Silveira, 2010).  Similarly, the exposed nests of M. pseudobrevis reported by Packer (1987) contained meloid beetles.  Although the population in Creston was not followed to document mortality, a number of females of Pteromalus were observed at the nesting sites (Fig. 6).  In natural nesting cavities, one would expect that individual natal cells are only subject to attack from parasites while the nest is being provisioned, though in thin-walled nesting cavities, some parasites (e.g., Leucospis affinis Say) can penetrate the lateral walls (Graenicher, 1906; Medler & Koerber, 1958).  Also typically observed is that the occupants emerge from the apical end of the natal cell, with individuals normally emerging from the apical to rear end of the nest (so as not to chew through their siblings).  In the nests in Creston, emer-gence holes were observed on the lateral edges of the leaf cells (Fig. 5), though these may have been from previous years, as females of this species are attracted to odors from old nests (Pitts-Singer, 2007), or from an earlier generation that year (Tepedino & Parker, 1986).  Although cavity-nesting bees will nest in a variety of cavities under natural settings, the flexibility reported in this study suggests that the Alfalfa Leafcut-ter Bee may also accept sub-optimal nesting sites.  This species also will accept a range of other artificial nesting cavities, including plastic straws, which have been shown to significantly decrease bee survival due to mold growth (Stephen & Every, 1970).  Plas-ticity in other aspects of nesting in this species, including the use of cut plastic bags Figure 6.  Pteromalus apum Retzius (Hymenoptera: Chalcididae), one of the main chalcid para-sites of the Alfalfa Leafcutter Bee.  Several adult P. apum were observed near the bee nesting population.Sheffield: Unusual nesting of Megachile rotundata2017 5ACKNOWLEDGEMENTSThanks to Terry Griswold, USDA-ARS Bee Biology and Systematics Laboratory, Utah State University for discussion, and two anonymous reviewers for helpful suggestions.  Thanks also to the Creston Museum for a delightful tour of the museum.REFERENCESCardoso, C.F., & F.A. Silveira. 2012. Nesting biology of two species of Megachile (Moureapis) (Hymenoptera: Megachilidae) in a semideciduous forest reserve in southeastern Brazil. Apidologie 43(1): 71–81.Eickwort, G.C., R.W. Matthews, & J. Carpenter. 1981. Observations on the nesting behavior of Megachile rubi and M. texana with a discussion of the significance of soil nesting in the evo-lution of megachilid bees (Hymenoptera:  Megachilidae). Journal of the Kansas Entomological Society 54(3): 557–570.Eves, J.D. 1970. Biology of Monodontomerus obscurus Westwood, a parasite of the alfalfa leaf-cutting bee, Megachile rotundata (Fabricius) (Hymenoptera: Torymidae: Megachilidae). Me-landeria 4: 1–18.Fortel, L.,  M. Henry, L. Guilbaud, H. Mouret, & B.E. Vaissière. 2016. Use of human-made nest-ing structures by wild bees in an urban environment. Journal of Insect Conservation 20(2): 239–253.Fye, R.E. 1965. Biology of Apoidea taken in trap nests in northwestern Ontario (Hymenoptera). The Canadian Entomologist 97(8): 863–877.Graenicher, S. 1906. On the habits and life-history of Leucospis affinis (Say). A parasite of bees. Bulletin of the Wisconsin Natural History Society 4(4): 153–159.Hobbs, G.A., & C.E. Lilly. 1954. Ecology of species of Megachile Latreille in the mixed prairie region of southern Alberta with special reference to pollination of alfalfa. Ecology 35(4): 453–462.Hobbs, G.A., & M.D. Krunic. 1971. Comparative behavior of three chalcidoid (Hymenoptera) parasites of the alfalfa leafcutter bee, Megachile rotundata, in the laboratory. The Canadian Entomologist 103(5): 674–685.Koerber, T., & J.T. Medler. 1958. A trap-nest survey of solitary bees and wasps in Wisconsin, with biological notes. Transactions of the Wisconsin Academy of Sciences, Arts and Letters 47: 53–63.Krombein, K.V. 1967. Trap-Nesting Wasps and Bees: Life Histories, Nests, and Associates. Smithson-ian Press; Washington, D.C.; vi+570 pp.MacIvor, J.S. In press. Cavity-nest boxes for solitary bees: A century of design and research. ApidologieMacIvor, J.S., & A.E. Moore. 2013. Bees collect polyurethane and polyethylene plastics as novel nest materials. Ecosphere 4(12): 155 [1–6].MacIvor, J.S., & L. Packer. 2015. ‘Bee hotels’ as tools for native pollinator conservation: A prema-ture verdict? PLoS ONE 10(3):e0122126 [1–13].Medler, J.T., & T.W. Koerber. 1958. Biology of Megachile relativa Cresson (Hymenoptera, Mega-chilidae) in trap-nests in Wisconsin. Annals of the Entomological Society of America 51(4): 337–344.Michener, C.D. 2007. The Bees of the World [2nd Edition]. Johns Hopkins University Press; Balti-more, MD; xvi+[i]+953 pp., +20 pls.O’Neill, K.M., & J.F. O’Neill. 2016. Brood parasitism of the resin bee Megachile campanulae (Rob-ertson) by Coelioxys modesta Smith (Hymenoptera: Megachilidae). Journal of the Kansas Ento-mological Society 89(2): 117–127.instead of (or in addition to) leaf pieces, has also been observed (MacIvor & Moore, 2013), though the long-term impacts of such material on bee survival need to be fur-ther evaluated.Journal of Melittology6 No. 69Orr, M.C., Z.M. Portman, & T.L. Griswold. 2015. Megachile (Megachile) montivaga (Hymenoptera: Megachilidae) nesting in live thistle (Asteraceae: Cirsium). Journal of Melittology 48: 1–6.Packer, L. 1987. The triungulin larva of Nemognatha (Pauronemognatha) punctulata LeConte (Co-leoptera: Meloidae) with a description of the nest of its host – Megachile brevis pseudobrevis Say (Hymenoptera: Megachilidae). Journal of the Kansas Entomological Society 60(2): 280–287.Pitts-Singer, T.L. 2007. Olfactory response of megachilid bees, Osmia lignaria, Megachile rotun-data, and M. pugnata, to individual cues from old nest cavities. Environmental Entomology 36(2): 402–408.Pitts-Singer, T.L., & J.H. Cane. 2011. The alfalfa leafcutting bee, Megachile rotundata: The world’s most intensively managed solitary bee. Annual Review of Entomology 56: 221–237.Ravoet, J., L. De Smet, I. Meeus, G. Smagghe, T. Wenseleers, & D.C. de Graaf. 2014. Widespread occurrence of honey bee pathogens in solitary bees. Journal of Invertebrate Pathology 122: 55–58.Richards, K.W. 1978. Comparisons of nesting materials used for the alfalfa leafcutter bee, Mega-chile pacifica (Hymenoptera: Megachilidae). The Canadian Entomologist 110(8): 841–846.Richards, K.W. 1984. Alfalfa leafcutter bee management in Western Canada. Agriculture Canada Pub-lication 1495E; Ottawa, Canada; 53 pp.Sheffield, C.S. 2008. Summer bees for spring crops? Potential problems with Megachile rotundata (Fab.) (Hymenoptera: Megachilidae) as a pollinator of lowbush blueberry (Ericaceae). Jour-nal of the Kansas Entomological Society 81(3): 276–287.Sheffield, C.S., P.G. Kevan, S.M. Westby, & R.F. Smith. 2008. Diversity of cavity-nesting bees (Hymenoptera: Apoidea) within apple orchards and wild habitats in the Annapolis Valley, Nova Scotia, Canada. The Canadian Entomologist 140(2): 235–249.Sheffield, C.S., C. Ratti, L. Packer, & T. Griswold. 2011. Leafcutter and mason bees of the genus Megachile Latreille (Hymenoptera: Megachilidae) in Canada and Alaska. Canadian Journal of Arthropod Identification 18: 1–107.Stephen, W.P. 1956. Notes on the biologies of Megachile frigida Smith and M. inermis Provancher (Hymenoptera: Megachilidae). Pan-Pacific Entomologist 32(3): 95–101.Stephen, W.P. 1961. Artificial nesting sites for the propagation of the leaf-cutter bee, Megachile (Eutricharaea) rotundata, for alfalfa pollination. Journal of Economic Entomology 54(5): 989–993.Stephen, W.P., & C.E. Osgood. 1965. Influence of tunnel size and nesting medium on sex ratios in a leaf-cutter bee, Megachile rotundata. Journal of Economic Entomology 58(5): 965–968.Stephen, W.P., & R.W. Every. 1970. Nesting media for the propagation of leaf cutter bees. Fact Sheet 175, Oregon State University Cooperative Extension Service; Corvallis, OR; 2 pp.Tepedino, V.J., & F.D. Parker. 1986. Effect of rearing temperature on mortality, second-gener-ation emergence, and size of adult in Megachile rotundata (Hymenoptera: Megachilidae). Journal of Economic Entomology 79(4): 974–977.Tscharntke, T., A. Gathmann, & I. Steffan-Dewenter. 1998. Bioindication using trap-nesting bees and wasps and their natural enemies: Community structure and interactions. Journal of Ap-plied Ecology 35(5): 708–719.Zillikens, A., & J. Steiner. 2004. Nest architecture, life cycle and cleptoparasite of the Neotropical leaf-cutting bee Megachile (Chrysosarus) pseudanthidioides Moure (Hymenoptera: Megachili-dae). Journal of the Kansas Entomological Society 77(3): 193–202.The Journal of Melittology is an international, open access journal that seeks to rapidly disseminate the results of research conducted on bees (Apoidea: Anthophila) in their broadest sense.  Our mission is to promote the understanding and conservation of wild and managed bees and to facilitate communication and collaboration among researchers and the public worldwide.  The Journal covers all aspects of bee research including but not limited to: anatomy, behavioral ecology, biodiversity, biogeography, chemical ecology, comparative morphology, conservation, cultural aspects, cytogenetics, ecology, ethnobiology, history, identification (keys), invasion ecology, management, melittopalynology, molecular ecology, neurobiology, occurrence data, paleontology, parasitism, phenology, phylogeny, physiology, pollination biology, sociobiology, systematics, and taxonomy.The Journal of Melittology was established at the University of Kansas through the efforts of Michael S. Engel, Victor H. Gonzalez, Ismael A. Hinojosa-Díaz, and Charles D. Michener in 2013 and each article is published as its own number, with issues appearing online as soon as they are ready.  Papers are composed using Microsoft Word® and Adobe InDesign® in Lawrence, Kansas, USA.A Journal of Bee Biology, Ecology, Evolution, & Systematicshttp://journals.ku.edu/melittologyISSN 2325-4467Journal of Melittology is registered in ZooBank (www.zoobank.org), and archived at the Univer-sity of Kansas and in Portico (www.portico.org).Editor-in-ChiefMichael S. EngelUniversity of KansasVictor H. GonzalezUniversity of KansasAssistant EditorsIsmael A. Hinojosa-DíazUniversidad Nacional Autónoma de México

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Unusual nesting behavior in Megachile (Eutricharaea) rotundata (Hymenoptera: Megachilidae)

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Unusual nesting behavior in Megachile (Eutricharaea) rotundata (Hymenoptera: Megachilidae)

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