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ARS Home » Pacific West Area » Logan, Utah » Pollinating Insect-Biology, Management, Systematics Research » Research » Research Project #425663

Research Project: Managing and Conserving Diverse Bee Pollinators for Sustainable Crop Production and Wildland Preservation

Location: Pollinating Insect-Biology, Management, Systematics Research

2018 Annual Report


1a. Objectives (from AD-416):
Objective 1: Improve the production and management of non-Apis bees such as blue orchard bees, bumble bees, and alfalfa leafcutting bees for crop pollination by increasing knowledge of bee nutritional needs and environmental effects on bee physiology (especially on diapause and overwintering). Sub-Objective 1.1: Identify the pollen and nectar requirements for maintaining non-Apis bee fitness, in both native and managed ecosystems. Sub-Objective 1.2: Develop a better understanding of the environmental factors that affect diapause in non-Apis bees, and develop methods to improve winter survival. Objective 2: Identify environmental (e.g. poor nutrition) and biological factors associated with bee declines (non-Apis species and the honey bee) and develop methods to diagnose and control non-Apis mortality, such as pollen ball and chalkbrood, that are caused by parasites, pathogens (e.g. Crithidia and viruses of bumble bees), and pesticides. Sub-Objective 2.1: For non-Apis bees, develop methods to control pests and diagnose and treat infectious diseases. Sub-Objective 2.2: Identify the primary environmental and biological factors that affect managed bee sustainability. Objective 3: Quantify bee forage in relation to floral resources and management practices, such as grazing and improve nesting design and strategies (e.g. using chemical cues to enhance nest location), to maximize bee pollination. Sub-Objective 3.1: Improve the reproduction and health of Megachile rotundata (alfalfa leafcutting bee) and native bees by providing non-crop floral resources. Sub-Objective 3.2: Improve production systems for managed non-Apis bees. Objective 4: Improve bee taxonomy and curation and identify mechanisms that affect bee diversity to enhance conservation efforts, particularly in relation to fire and climate change. Sub-Objective 4.1: Expand the taxonomy and systematics of native bees and develop user-friendly identification keys. Sub-Objective 4.2: Evaluate bee biodiversity and improve the knowledge needed to achieve effective bee conservation and stewardship. Sub-Objective 4.3: Evaluate the effect of habitat-altering events on bee diversity and abundance, especially the effects of fire. Sub-Objective 4.4: Identify climatic factors that define the ranges, phenologies and population persistence of select native bees.


1b. Approach (from AD-416):
Bees are vital to agriculture. The commercial production of more than 90 crops is accomplished through bee pollination. The honey bee is the best known crop pollinator, but unfortunately, honey beekeepers have been facing a recent bee health crisis. Although a significant amount of scientific time and effort has been invested into identifying the causes for poor colony health, the issue can be viewed as a more general problem, the declining availability of pollinators for agriculture and ecosystems. In addition to working toward finding solutions to the health issues facing honey bees, we provide another approach: tapping into the pollination potential of the diverse bee fauna of the U.S. This project plan addresses four main objectives: (1) improve non-Apis bee production and management systems, (2) develop methods to control pathogens and parasites and identify environmental stressors for all bees, (3) understand the foraging and nutritional needs of non-Apis bees, and (4) improve bee systematics and taxonomy and our knowledge of bee diversity. Our overriding goal is to provide agriculture with a tool box of pollinators. To achieve this, we must provide a better understanding of the causes behind pollinator declines, improve pollinator availability, and better understand how bee population size and density affect crop pollination. Of necessity, this requires addressing diseases and parasites, environmental impacts, and human-induced threats such as pesticides and habitat loss. Equally important is wild bee diversity. Wild bees provide free pollination services for agricultural crops, maintain plant reproduction in natural areas, and ensure a pool of future managed pollinators.


3. Progress Report:
This report summarizes progress for this project which began October 1, 2013 and terminates September 30, 2018. Research will be continued under the bridging project 2080-21000-017-00D, “Managing and Conserving Diverse Bee Pollinators for Sustainable Crop Production and Wildland Preservation”, while the research plan for the next five years undergoes peer panel Office of Scientific Quality Review. Of the more than 20,000 bee species worldwide, only a small fraction of species has been successfully managed to pollinate agricultural crops. ARS scientists in Logan, Utah, continue research to improve production and management of several species of social and solitary bees currently managed in agricultural systems, and to seek novel pollinators to meet pollination needs. This project had four goals: (1) improve non-Apis bee production and management systems, (2) develop methods to control pathogens and parasites and identify environmental stressors for all bees, (3) understand the foraging and nutritional needs of non-Apis bees, and (4) improve bee systematics and taxonomy and our knowledge of bee diversity. Since 2013, ARS scientists in Logan, Utah, have reported research on solitary bees, bumble bees, and honey bees of relevance to the general public, alfalfa seed producers, almond growers, fruit growers, bumble bee producers, honey bee keepers, tomato producers, and agencies such as: the Animal and Plant Health Inspection Service (APHIS) Plant Protection and Quarantine Program, the U.S. Forest Service (USFS), the Natural Resources Conservation Service (NRCS), the U.S. Fish and Wildlife Service (FWS), the Bureau of Land Management (BLM), the National Parks Service (NPS), U.S. Geological Services (USGS), and U.S. Environmental Protection Agency (EPA). Consultation and expertise have been provided to private citizens and to non-profit conservation groups such as the Xerces Society for Invertebrate Conservation, North American Pollinator Protection Campaign, and the Saint Louis Zoo. Consultation was provided to the Tribal Pesticide Program Council representing Native American Nations with guidance on Managed Pollinator Protection Plans. ARS researchers have informed regulatory agencies and ag/chem industries on the biology of native bees and how their risk of exposure to agrichemical products may be potentially greater than honey bees, given major differences in nesting and provisioning behaviors. With increased focus on native bees, ARS scientists in Logan, Utah, have actively collaborated in development and design of native bee surveys. For improved non-Apis bee production and management systems, significant progress was realized on using Blue Orchard Bees (BOB) (Osmia lignaria) in crop production. In almonds, BOBs, when co-deployed with honey bees, result in an increased fruit set. Economical models were developed, enabling growers to explore inputs into almond systems and elucidating economic impacts of adding BOB’s. The management and deployment of BOBs benefited from development of best management practices (BMPs) that maximize pollination and bee reproduction (guaranteeing pollinator availability for the next season). ARS patented and successfully licensed a spray-on-lure for nesting to encourage BOBs to stay in orchards and effectively pollinate. The BMPs for using BOBs has been transferred to commercial companies and the services of these companies is now in demand by numerous almond growers. This research is now being conducted in other fruit crops like sweet and tart cherries and apples. For several crops (almonds and raspberries), ARS scientists in Logan, Utah, have collaborated with university researchers to develop “Integrated Crop Pollination” (ICP) strategies to maximize profits and ensure sustainable pollination of bee-dependent crops. ICP emphasizes combining tactics that are appropriate for a crop’s dependence on insect-mediated pollination and include use of wild and managed bee species and enhancing the environment for pollinators through directed habitat management and pesticide stewardship. This approach has been transferred to growers to enable them to decide on the most efficient way to apply ICP to maximize profits. Bumble bee populations have been described, creating the major database in the U.S. for bumble bee distributions. In addition, pathogen and parasite loads in these species were determined. These data were provided to USDA-APHIS and the U.S. Fish and Wildlife to help address health-related concerns. For commercial production of bumble bees, two western species were developed, and these bees have been transferred to companies that produce and sell bumble bee colonies for pollination. Production of bumble bees for commercial pollination or for efforts to restore endangered species was supported by finding the best methods to sterilize pollen (bumble bees are fed pollen collected by honey bees that may contain pathogens). Additional research has shown that larger tomatoes are grown in greenhouses when pollinated by bumble bees. Further research is being done on greenhouse use of bumble bees. The second goal, developing methods to control pathogens and parasites and identifying environmental stressors for all bees, progress was made on identifying pathogens in different bee species. For bumble bees and alfalfa leaf cutting bees (ALCB), several viruses, Chalkbrood fungi, nosema, and protozoan parasites were identified. The host specificity of Chalkbrood species was determined. In ALCB, progress was made in describing the association of a parasitoid wasp (Mellitobia), defining its species identity, and determining its distribution. New parasites (queen castrating parasitic nematodes) were found in bumble bees that may be important mortality factors in some species. Impacts of commonly used organosilicone spray adjuvants and pesticides were determined for honey bees, bumble bees, and solitary bees. Both honey bees and bumble bees have decreased survivorship when fed organosilicones at low concentration; in honey bee larvae, the adjuvants synergize with viral infections. Fungicides, insecticides, and spray adjuvants were found to disrupt nesting behavior of solitary bees. The insect growth regulator novaluron was found to be ovicidal and disrupt larval growth in alfalfa leaf cutting bees. This information was shared with grower groups to help develop practices to promote pollinator health and pollination of crops. The transcriptomes of both the Hunt bumble bee and the alfalfa leaf cutting bee have been described and provide valuable resources for investigating the responses of bees to pathogens and xenobiotics such as pesticides. The third goal, understanding the foraging and nutritional needs of non-Apis bees, the role of pollen and nectar in bee diets has been examined, with demonstration that some solitary bee species require pollen as adults for egg formation. Preliminary data indicate that nectar is essential to solitary bee survival and reproduction, providing critical information on how to support bees when emergence and release are disrupted in managed pollination. Novel methods demonstrated that solitary bees transmit pollen from one patch of flowers to another remotely located patch, even after depositing pollen in nests. This research is important in understanding how to maintain purity in crop seeds and how to maximize genetic outcrossing in native plant species with restricted populations. Towards this goal, progress has been made on understanding the pollen needs of developing larvae for both ground nesting bees and bumble bees. The development of a new pollen trap has facilitated pollen studies in bumble bees. Bumble bees were found to forage on different floral hosts than honey bees when co-located. Novel methods for tracking bee movement have been developed in collaboration with ARS colleagues in Maricopa, Arizona, and can be used over time without killing the bees. Marker proteins and dyes are facilitating the tracking of bumble bees in green houses and are useful for monitoring movement out of and back into greenhouses. For solitary bees like Blue Orchard Bees, these dyes do persist on bees and will be used to monitor foraging distance and pollination. The impact of wild fires on bee populations and their host plants has been determined. Ground nesting bees and many floral hosts that have deep taproots can survive intense fires. Normal cycles of fire may also promote floral resources, creating larger populations of pollinators in natural forest areas. Research has defined pollinator beneficial plants in the western U.S. that can be used in reclamation of natural lands following wildfires. The fourth goal, improve bee systematics and taxonomy and our knowledge of bee diversity, the number of specimens in the U.S. National Pollinating Insect Collection has increased since 2013 from 1.1 million to over 1.7 million and its publicly available database, U.S. National Pollinating Insect Database, increased from 600,000 records to over 2.1 million records. Several new species have been described and revision of major groups has been made to improve species identifications. Some new species have unique biology not previously known, like the bee making its nests in sandstone in the southwest. Surveys have been conducted in several areas in the southwest and in western National Parks in collaboration with USGS, FWS, Utah Cooperative Agricultural Pest Survey Program, and the National Park Service NPS. In collaboration with USDA-APHIS and Utah State University, progress is being made on creating a pictorial key for identification of native and potentially invasive Osmia species for use by port inspectors. New molecular methods have been developed that can resolve issues associated with bee systematics and that will be of use in bee identification by non-specialists.


4. Accomplishments
1. Development of detection methods of diseases in bumble bees helps to ensure their health and survival. Commercial production of healthy bumble bee colonies is critical for agriculture, especially for greenhouse production of crops such as tomatoes. Yet, detection methods for several bumble bee diseases are insensitive and have been shown to be unreliable at detecting disease variants. ARS scientists in Logan, Utah, developed molecular tools for detection of a group of disease-causing agents that commonly infect bumble bees in agro-ecosystems. These tools facilitate rapid disease detection and identification in bumble bee production facilities and promote efforts for species recovery of endangered bumble bees.

2. The importance of pollinator phylogenetic diversity for crop production. Bees are responsible for pollinating most of our most valuable and nutritious crops, but habitat loss and agricultural intensification have been implicated in recent bee declines, potentially threatening food security. With molecular tools developed by ARS scientists in Logan, Utah, in collaboration with researchers at Cornell University, the genetic diversity of bees in eastern apple orchards and their relatedness was quantified with molecular data and combined with data on bee abundance, bee biology, fruit quality and yield, and land use patterns around orchards. It was found that orchards with more bee species and greater genetic diversity within species had improved crop yield and quality in apples. These results indicate that conservation of, not only the number of bee species, but also their genetic diversity is important for maximal crop production.

3. Hidden diversity found in two agriculturally important bee species. The native bee species, Osmia lignaria and Osmia ribifloris, are important pollinators of crop plants in the U.S. Despite their increasing use as managed pollinators, uncertainty exists regarding species-level and population-level diversity within both groups. Using state-of-the-art genomic data, ARS researchers in Logan, Utah, examined the genetic diversity within these bees and discovered multiple cryptic lineages within each species, indicating that the traditional species groups may be genetically distinct bee lineages (i.e. new species). Understanding this natural diversity helps researchers and beekeepers alike identify species, improve management practices, and conserve nature.

4. Determining how wild fires can impact the fate of native bees and their host plants. The fates of native bee communities in the Great Basin sagebrush steppe are linked with the susceptibilities of their floral hosts to increasingly frequent wildfires. ARS scientists in Logan, Utah, quantified post-fire survival and subsequent flowering of six prevalent perennial wildflowers across a range of fire severities using novel methods. At maximal fire severity, the impacts ranged from 80 percent survival to complete mortality. Several wild flowers survived well but many survivors failed to flower the year after burning. The post-fire fates of these plant/pollinator interactions depend upon where the bees nest, the floral host’s sensitivity to a given burn intensity, both in terms of survival and flowering, and the reproductive interdependence of bee and floral hosts (floral specialists versus generalists). These research results help predict the impact of wild fires upon the essential pollinators that are needed for flower reproduction and a healthy natural ecosystem.

5. Effective pollen sterilization methods developed for bumble bee production. Bumble bee colonies that are raised in captivity for commercial pollination must be fed pollen collected from honey bee hives; however, this poses a risk of pathogen transfer to the bumble bee colonies. ARS scientists in Logan, Utah, subjected pollen to treatments of ethylene oxide, ozone or gamma irradiation to kill or inactivate fungal diseases and viral pathogens in the pollen. The pollen was then tested for viability of the pathogens and for post-treatment nutrition for the bees. Results indicate that ethylene oxide and gamma irradiation are both highly effective in killing pathogens, but that ethylene oxide remained more palatable to the bees after treatment. This provides a new and more effective form of sterilization of pollen for commercial bumble bee producers, ensuring healthy bee production.

6. Protein markers and dyes for tracking movement of managed bees can be used without killing bees. ARS scientists in Logan, Utah, and Maricopa, Arizona tested the ability to detect a protein (egg albumin) marker on live bumble bees, blue orchard bees, and alfalfa leafcutting bees without having to kill them in the process. Rinses of live bees and subsequent detection proved 100 percent efficient and did not have a negative impact on bee survivorship. This method can be used as a reliable and valid surrogate to traditional, destructive sampling methods for mark-capture bee studies performed in open landscapes. This method is valuable in tracking bee dispersal from release sites and the retention of managed pollinators in commercial crops.

7. Rich bee fauna in the Colorado Plateau may provide a reservoir of pollinators. Despite concern about declines in bee abundance and diversity, little is known about what bees are present, and in what abundance, for most natural areas. In wild lands bees not only provide essential pollination for native plants, they are also extracted for use as crop pollinators (e.g. blue orchard bee). Results of a four-year, all flowering-season study of native bees in the Colorado Plateau region of southern Utah completed by ARS researchers in Logan, Utah, documented 648 bee species, making it one of the richest bee faunas in the West. Bees visit a large portion of the flora of Grand Staircase Escalates National Monument, with a few plants attracting an inordinate number of species and individuals. The occurrence of increasing drought has a negative impact on bee abundance and diversity, but despite these conditions, bees are flourishing in this region.

8. Sources of pollen and leaf pieces impact the microbiome of larval pollen provisions and may have role in plant pathogen movement. Managed pollinators such as the alfalfa leafcutting bee, Megachile rotundata, are essential to the production of a wide variety of agricultural crops. These pollinators encounter a diverse array of microbes when foraging for food and nest-building materials on various plants. To ascertain how the food and nest-building materials affects the composition of the bee-nest microbiome, ARS scientists in Logan, Utah, and their collaborators exposed M. rotundata adults to treatments that varied both floral and foliar sources. Alfalfa and blue tansy as pollen sources and buckwheat and nasturtium leaves for nest building were available. Both the bacterial and fungal communities were quite diverse and contained numerous species of known plant and bee pathogens that differed among the pollen and leaf sources. This research indicates that bees deposit plant-associated microbes into their nests, including multiple plant pathogens such as smut fungi and bacteria that cause blight and wilt.

9. Determination of the pollination efficiency of bee species for red raspberry production. Production of the commercial red raspberry is currently reliant on honey bees for pollination. Previously, the recommended stocking density of honey bees for raspberry production was two to five colonies per hectare, with the assumption that a raspberry flower required dozens of daily floral visits to achieve maximize fruit size. ARS scientists in Logan, Utah, found that three species of Osmia bees and a bumble bee species are all equally as effective as honey bees in pollinating raspberries. Use of the alternative pollinators is more cost-effective for production in high tunnels but not open-fields. For three red raspberry cultivars examined, experiments demonstrated that fully-sized raspberries resulted from flowers visited just twice by a bee. This research indicates that current stocking density recommendations greatly over-estimate the number of colonies required for adequate pollination and provides a better estimation of needed bee numbers for raspberry production.

10. Honeydew secreted by scale insects is discovered to be significant food source for native bees. ARS scientists in Logan, Utah, observed 42 species of wild bees visiting nonflowering shrubs. Experiments demonstrated that these bees were accessing sugary honeydew secretions from scale insects. While honeydew use is known for honey bees, its use across a diverse community of solitary bees is a novel observation. This research finding helps to outline how native bees cope with scarcity of floral resources and increasing environmental change offers a way to promote bee health when flowers are not available.

11. Bee identifications are essential to bee conservation in agricultural and natural ecosystems. Essential information on species identifications, biology, distribution, and seasonality of native bees is needed both for developing managed bees in crop environments and conservation of bees in natural ecosystems. ARS scientists in Logan, Utah, made significant progress in resolving the identification and biologies of more than 50 bee species. An additional 45,000 specimens have been added to the United States National Pollinating Insects Collection in Logan, Utah, making it the largest collection of bees in the world with approximately 1.6 million specimens from 136 countries. An additional 600,000 data-records have been entered into a specimen-level database that now totals more than 2.1 million records. Using these valuable resources, ARS scientists collaborate with researchers from around the world to identify bees and aid in native bees’ surveys to determine the health of native bees. This research is essential to ensuring adequate pollination of crops and plants in natural ecosystems.


Review Publications
Koh, I., Lonsdorf, E.V., Artz, D.R., Pitts-Singer, T., Ricketts, T.H. 2017. Ecology and economics of using native managed bees for almond pollination. Ecological Applications. 111(1):16-25. https://doi.org/10.1093/jee/tox318.

Griswold, T.L., Rightmyer, M.G. 2017. A revision of the subgenus Osmia (Diceratosmia), with descriptions of four new species (Hymenoptera, Megachilidae). Zootaxa. 4337:1. http://dx.doi.org/10.11646/zootaxa.4337.1.1.

Portman, Z.M., Griswold, T.L. 2017. Review of Perdita subgenus Procockerellia Timberlake (Hymenoptera: Andrenidae) and the first Perdita gynandromorph. ZooKeys. 712:87-111.

Muller, A., Griswold, T.L. 2017. Osmiine bees of the genus Haetosmia (Megachilidae, Osmiini): Biology, taxonomy and key to species. Zootaxa. 4358(2):351–364. http://dx.doi.org/10.11646/zootaxa.4358.2.8.

Griswold, T.L. 2018. First record of Stenoheriades Cockerell in tropical Asia: Stenoheriades bifida, new species (Hymenoptera: Megachilidae). Zootaxa. 4370(3):279–282. http://dx.doi.org/10.11646/zootaxa.4370.3.7.

Meza-Lazaro, R.N., Poteaux, C., Bayona-Vásquez, N.J., Branstetter, M.G., Zaldívar-Riverón, A. 2018. Extensive mitochondrial heteroplasmy in the neotropical ants of the Ectatomma ruidum complex (Formicidae: Ectatomminae). Mitochondrial DNA, Part A. http://dx.doi.org/10.1080/24701394.2018.1431228.

Tripodi, A.D., Strange, J.P., Szalanski, A.L. 2018. Novel multiplex PCR reveals multiple trypanosomatid species infecting North American bumble bees (Hymenoptera: Apidae: Bombus). Journal of Invertebrate Pathology. 153:147-155.

Pitts-Singer, T., Artz, D.R., Peterson, S.L., Boyle, N.K., Wardell, G.I. 2018. Examination of a managed pollinator strategy for almond production using Apis mellifera (Hymenoptera: Apidae) and Osmia lignaria (Hymenoptera: Megachilidae). Environmental Entomology. 47(2):364-377. https://doi.org/10.1093/ee/nvy009.

Longino, J.T., Branstetter, M.G. 2018. The truncated bell: an enigmatic but pervasive elevational diversity pattern in Middle American ants. Ecography. 41:1-12. https://doi.org/10.1111/ecog.03871.

Cane, J.H., Tepedino, V.J. 2016. Gauging the effect of honey bee pollen collection on native bee communities. Conservation Letters. 10(2):205-210. https://doi.org/10.1111/conl.12263.

Cane, J.H., Love, B.G. 2016. Floral guilds of bees in sagebrush steppe: Comparing bee usage of wildflowers available for postfire restoration. Natural Areas Journal. 36(4):377-391.

Cane, J.H. 2016. Specialist bees collect Asteraceae pollen by distinctive abdominal drumming (Osmia) or brushing (Melissodes, Svastra). Arthropod-Plant Interactions. 11:257-261.

Cane, J.H. 2018. Co-dependency between a specialist Andrena bee and its death camas host, Toxicoscordion paniculatum. Arthropod-Plant Interactions. https://doi.org/10.1007/s11829-018-9626-9.

Vanengelsdorp, D., Traynor, K.S., Andree, M., Lichtenberg, E.M., Chen, Y., Saegerman, C., Cox-Foster, D.L. 2017. Colony collapse disorder (CCD) and bee age impact honey bee pathophysiology. PLoS Pathogens. 12(7):e0179535. https://doi.org/10.1371/journal.pone.0179535.

Portman, Z.M., Griswold, T.L. 2016. An anomalous specimen of Perdita wasbaueri Timberlake with only one antenna (Hymenoptera: Andrenidae). Journal of Kansas Entomological Society. 89(3):267-269.

Meiners, J., Griswold, T.L., Morgan, E.S. 2017. Bees without flowers: Before peak bloom, diverse native bees find insect-produced honeydew sugars. The American Naturalist. 190(2):281-291. http://dx.doi.org/10.1086/692437.

Bystriakova, N., Griswold, T.L., Ascher, J.S., Kuhlmann, M. 2017. Key environmental determinants of global and regional richness patterns for a wild bee subfamily. Biodiversity and Conservation Journal. https://doi.org/10.1007/s10531-017-1432-7.

Kumar, V., Griswold, T.L., Velavadi, V.V. 2017. The Resin and Carder bees of south India (Hymenoptera: Megachilidae: Anthidiini). Zootaxa. 4317(3):436–468.

Fischman, B.J., Pitts-Singer, T., Robinson, G.E. 2017. Nutritional regulation of phenotypic plasticity in a solitary bee. Environmental Entomology. 46(5):1070-1079. https://doi.org/10.1093/ee/nvx119.

Kopit, A., Pitts-Singer, T. 2018. Routes of pesticide exposure in solitary, cavity-nesting bees. Environmental Entomology. 47(3):499-510. https://doi.org/10.1093/ee/nvy034.

Isaacs, R., Williams, N., Ellis, J., Pitts-Singer, T., Bommarco, R., Vaughn, M. 2017. Integrated crop pollination: Combining strategies to ensure stable and sustainable yields of pollination-dependent crops. Basic and Applied Ecology. 22:44-60. https://doi.org/10.1016/j.baae.2017.07.003.

Parys, K.A., Griswold, T.L., Ikerd, H.W., Orr, M.C. 2018. New records and range extensions of several species of native bees (Hymenoptera: Apoidea) from Mississippi. Biodiversity Data Journal. 6:e25230. https://doi.org/10.3897/BDJ.6.e25230.

Branstetter, M.G., Childers, A.K., Cox-Foster, D.L., Hopper, K.R., Kapheim, K.M., Toth, A.L., Worley, K.C. 2018. Genomes of the Hymenoptera. Current Opinion in Insect Science. 25:65-75. https://doi.org/10.1016/j.cois.2017.11.008.

Achik, D., Lopez-Uribe, M.M., Griswold, T.L., Praz, C.J., Danforth, B.N. 2017. Phylogeny and new generic-level classification, and historical biogeography of the Eucera complex (Hymenoptera: Apidae). Molecular Phylogenetics and Evolution. 119:81-92.