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Rivest S, Lee ST, Cook D, Forrest JRK. Consequences of pollen defense compounds for pollinators and antagonists in a pollen-rewarding plant. Ecology 2024; 105:e4306. [PMID: 38590050 DOI: 10.1002/ecy.4306] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/27/2023] [Revised: 01/09/2024] [Accepted: 02/19/2024] [Indexed: 04/10/2024]
Abstract
Plants produce an array of defensive compounds with toxic or deterrent effects on insect herbivores. Pollen can contain relatively high concentrations of such defense compounds, but the causes and consequences of this enigmatic phenomenon remain mostly unknown. These compounds could potentially protect pollen against antagonists but could also reduce flower attractiveness to pollinators. We combined field observations of the pollen-rewarding Lupinus argenteus with chemical analysis and laboratory assays to test three hypotheses for the presence of pollen defense compounds: (1) these compounds are the result of spillover from adjacent tissues, (2) they protect against pollen thieves, and (3) they act as antimicrobial compounds. We also tested whether pollen defense compounds affect pollinator behavior. We found a positive relationship between alkaloid concentrations in pollen and petals, supporting the idea that pollen defense compounds partly originate from spillover. However, pollen and petals exhibited quantitatively (but not qualitatively) distinct alkaloid profiles, suggesting that plants can adjust pollen alkaloid composition independently from that of adjacent tissues. We found no relationship between pollen alkaloid concentration and the abundance of pollen thieves in Lupinus flowers. However, pollen alkaloids were negatively associated with bacterial abundance. Finally, plants with more alkaloids in their pollen received more pollinator visits, but these visits were shorter, resulting in no change in the overall number of flowers visited. We propose that pollen defense compounds are partly the result of spillover from other tissues, while they also play an antimicrobial role. The absence of negative effects of these compounds on pollinator visitation likely allows their maintenance in pollen at relatively high concentrations. Taken together, our results suggest that pollen alkaloids affect and are mediated by the interplay of multiple interactions.
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Affiliation(s)
- Sébastien Rivest
- Department of Biology, University of Ottawa, Ottawa, Ontario, Canada
- Rocky Mountain Biological Laboratory, Crested Butte, Colorado, USA
| | - Stephen T Lee
- USDA ARS Poisonous Plant Research Laboratory, Logan, Utah, USA
| | - Daniel Cook
- USDA ARS Poisonous Plant Research Laboratory, Logan, Utah, USA
| | - Jessica R K Forrest
- Department of Biology, University of Ottawa, Ottawa, Ontario, Canada
- Rocky Mountain Biological Laboratory, Crested Butte, Colorado, USA
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Rivest S, Muralidhar M, Forrest JRK. Pollen chemical and mechanical defences restrict host-plant use by bees. Proc Biol Sci 2024; 291:20232298. [PMID: 38471551 PMCID: PMC10932708 DOI: 10.1098/rspb.2023.2298] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2023] [Accepted: 01/31/2024] [Indexed: 03/14/2024] Open
Abstract
Plants produce an array of chemical and mechanical defences that provide protection against many herbivores and pathogens. Putatively defensive compounds and structures can even occur in floral rewards: for example, the pollen of some plant taxa contains toxic compounds or possesses conspicuous spines. Yet little is known about whether pollen defences restrict host-plant use by bees. In other words, do bees, like other insect herbivores, tolerate the defences of their specific host plants while being harmed by non-host defences? To answer this question, we compared the effects of a chemical defence from Lupinus (Fabaceae) pollen and a putative mechanical defence (pollen spines) from Asteraceae pollen on larval survival of nine bee species in the tribe Osmiini (Megachilidae) varying in their pollen-host use. We found that both types of pollen defences reduce larval survival rate in some bee species. These detrimental effects were, however, mediated by host-plant associations, with bees being more tolerant of the pollen defences of their hosts, relative to the defences of plant taxa exploited by other species. This pattern strongly suggests that bees are adapted to the pollen defences of their hosts, and that host-plant use by bees is constrained by their ability to tolerate such defences.
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Affiliation(s)
- Sébastien Rivest
- Department of Biology, University of Ottawa, Ottawa, ON, Canada K1N 6N5
- Rocky Mountain Biological Laboratory, Crested Butte, CO 81224, USA
| | | | - Jessica R. K. Forrest
- Department of Biology, University of Ottawa, Ottawa, ON, Canada K1N 6N5
- Rocky Mountain Biological Laboratory, Crested Butte, CO 81224, USA
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Wood TJ, Müller A, Praz C, Michez D. Elevated rates of dietary generalization in eusocial lineages of the secondarily herbivorous bees. BMC Ecol Evol 2023; 23:67. [PMID: 37986035 PMCID: PMC10662511 DOI: 10.1186/s12862-023-02175-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2023] [Accepted: 11/16/2023] [Indexed: 11/22/2023] Open
Abstract
BACKGROUND Within the Hymenoptera, bees are notable for their relationship with flowering plants, being almost entirely dependent on plant pollen and nectar. Though functionally herbivorous, as a result of their role as pollinators, bees have received comparatively little attention as models for insect herbivory. Bees often display dietary specialization, but quantitative comparison against other herbivorous insects has not previously been conducted. RESULTS In the most comprehensive analysis to date for 860 bee species, dietary specialization amounted to 50.1% of studied species collecting pollen from between 1 and 2 botanical families with a relatively long tail of dietary generalists, with 11.1% of species collecting from more than 10 botanical families. This distribution deviated from the truncated Pareto distribution of dietary breadth seen in other herbivorous insect lineages. However, this deviation was predominantly due to eusocial bee lineages, which show a range of dietary breadths that conformed to a normal distribution, while solitary bees show a typical truncated distribution not strongly different from other herbivorous insects. We hypothesize that the relatively low level of dietary specialization in bees as a whole reflects the relaxation of the constraints typically observed in herbivorous insects with a comparatively reduced importance of plant chemistry and comparatively increased importance of phenology and foraging efficiency. The long flight periods of eusocial bees that are necessary to allow overlapping generations both allows and necessitates the use of multiple flowering resources, whereas solitary bees with short flight periods have more limited access to varied resources within a constrained activity period. CONCLUSIONS Collectively, solitary bees show slightly lower specialization compared to other herbivorous insects, possibly due to their balanced relationship with plants, rather than direct antagonism such as seen in the direct consumption of plant tissues. An additional factor may be the mediocre diversity of bees at low latitudes combined with low levels of dietary specialization, whereas these areas typically display a high rate of specialization by herbivorous insects in general. Though the most important factors structuring dietary specialization in bees appear to differ from many other herbivorous insects, solitary bees show a surprisingly similar overall pattern of dietary specialization.
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Affiliation(s)
- T J Wood
- University of Mons, Research Institute for Biosciences, Laboratory of Zoology, Place du parc 20, 7000, Mons, Belgium.
| | - A Müller
- ETH Zurich, Institute of Agricultural Sciences, Biocommunication and Entomology, Schmelzbergstrasse 9/LFO, 8092, Zurich, Switzerland
| | - C Praz
- University of Neuchâtel, Institute of Biology, Rue Emile-Argand 11, 2000, Neuchâtel, Switzerland
- InfoFauna - Swiss Zoological Records Center, Avenue de Bellevaux 51, 2000, Neuchâtel, Switzerland
| | - D Michez
- University of Mons, Research Institute for Biosciences, Laboratory of Zoology, Place du parc 20, 7000, Mons, Belgium
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Hao K, Xu Q, Huang SQ. Pollen-feeding behavior of diverse insects on Geranium delavayi, a flower with large, accessible pollen grains. AMERICAN JOURNAL OF BOTANY 2023; 110:e16113. [PMID: 36462154 DOI: 10.1002/ajb2.16113] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/27/2022] [Revised: 11/21/2022] [Accepted: 11/22/2022] [Indexed: 06/17/2023]
Abstract
PREMISE Why have pollen grains evolved to be exceptionally large in some species? Pollen-feeding hypothesis suggests that if the proportion of pollen amounts for feeding is reduced in a flower, the low allocation to pollen number would allow pollen grains to be larger. METHODS To examine whether species with large pollen grains experience low pollen consumption, the behavior of insects feeding on nectar and pollen was observed and pollen transfer efficiency was estimated for four visitor types in Geranium delavayi. To see whether bees actively collected pollen, the numbers of grains in pollen baskets and on the body were compared. Both nutritional value (total protein and lipid) and chemical defense (phenolic metabolites) in pollen against pollen feeders were measured. RESULTS Bumblebees and honeybees foraged for nectar, rarely groomed pollen into corbiculae, and had >5× higher pollen transfer efficiency than smaller solitary bees and flies, which were pollen eaters that removed more pollen but deposited less. Pollen grains were characterized by low protein and high lipid content with a low protein-lipid ratio, an unfavorable combination for bumblebees. Three secondary metabolites were significantly higher in pollen grains (7.77 mg/g) than in petals (1.08 mg/g) or in nectar (0.44 mg/g), suggesting stronger chemical defense in pollen. CONCLUSIONS Our results indicated that large bees took nectar but little of the nutritionally poor and highly toxic pollen. These data support one prediction of the pollen-feeding hypothesis, that species with few and large pollen grains would also have low pollen-consumption rates.
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Affiliation(s)
- Kai Hao
- Institute of Evolution and Ecology, School of Life Sciences, Central China Normal University, Wuhan, 430079, China
- Key Laboratory of Plant Resources Conservation and Sustainable Utilization, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, 510650, China
| | - Qi Xu
- Institute of Evolution and Ecology, School of Life Sciences, Central China Normal University, Wuhan, 430079, China
| | - Shuang-Quan Huang
- Institute of Evolution and Ecology, School of Life Sciences, Central China Normal University, Wuhan, 430079, China
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Brenzinger K, Maihoff F, Peters MK, Schimmer L, Bischler T, Classen A. Temperature and livestock grazing trigger transcriptome responses in bumblebees along an elevational gradient. iScience 2022; 25:105175. [PMID: 36204268 PMCID: PMC9530833 DOI: 10.1016/j.isci.2022.105175] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2022] [Revised: 08/26/2022] [Accepted: 09/19/2022] [Indexed: 11/22/2022] Open
Abstract
Climate and land-use changes cause increasing stress to pollinators but the molecular pathways underlying stress responses are poorly understood. Here, we analyzed the transcriptomic response of Bombus lucorum workers to temperature and livestock grazing. Bumblebees sampled along an elevational gradient, and from differently managed grassland sites (livestock grazing vs unmanaged) in the German Alps did not differ in the expression of genes known for thermal stress responses. Instead, metabolic energy production pathways were upregulated in bumblebees sampled in mid- or high elevations or during cool temperatures. Extensive grazing pressure led to an upregulation of genetic pathways involved in immunoregulation and DNA-repair. We conclude that widespread bumblebees are tolerant toward temperature fluctuations in temperate mountain environments. Moderate temperature increases may even release bumblebees from metabolic stress. However, transcriptome responses to even moderate management regimes highlight the completely underestimated complexity of human influence on natural pollinators. Upregulation of energy metabolism pathways in Bombus lucorum with increasing elevation Genes known for thermal stress responses did not change with increased elevation Bombus lucorum are tolerant toward relatively broad temperature fluctuations Grazing lead to an upregulation in genetic information processes in B. lucorum
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Affiliation(s)
- Kristof Brenzinger
- Department of Animal Ecology and Tropical Biology, Biocenter, University of Würzburg, 97074 Würzburg, Germany
- Corresponding author
| | - Fabienne Maihoff
- Department of Animal Ecology and Tropical Biology, Biocenter, University of Würzburg, 97074 Würzburg, Germany
| | - Marcell K. Peters
- Department of Animal Ecology and Tropical Biology, Biocenter, University of Würzburg, 97074 Würzburg, Germany
| | - Leonie Schimmer
- Department of Animal Ecology and Tropical Biology, Biocenter, University of Würzburg, 97074 Würzburg, Germany
| | - Thorsten Bischler
- Core Unit Systems Medicine, University of Würzburg, 97080 Würzburg, Germany
| | - Alice Classen
- Department of Animal Ecology and Tropical Biology, Biocenter, University of Würzburg, 97074 Würzburg, Germany
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Klečka J, Mikát M, Koloušková P, Hadrava J, Straka J. Individual-level specialisation and interspecific resource partitioning in bees revealed by pollen DNA metabarcoding. PeerJ 2022; 10:e13671. [PMID: 35959478 PMCID: PMC9359135 DOI: 10.7717/peerj.13671] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2021] [Accepted: 06/12/2022] [Indexed: 01/17/2023] Open
Abstract
It is increasingly recognised that intraspecific variation in traits, such as morphology, behaviour, or diet is both ubiquitous and ecologically important. While many species of predators and herbivores are known to display high levels of between-individual diet variation, there is a lack of studies on pollinators. It is important to fill in this gap because individual-level specialisation of flower-visiting insects is expected to affect their efficiency as pollinators with consequences for plant reproduction. Accordingly, the aim of our study was to quantify the level of individual-level specialisation and foraging preferences, as well as interspecific resource partitioning, in three co-occurring species of bees of the genus Ceratina (Hymenoptera: Apidae: Xylocopinae), C. chalybea, C. nigrolabiata, and C. cucurbitina. We conducted a field experiment where we provided artificial nesting opportunities for the bees and combined a short-term mark-recapture study with the dissection of the bees' nests to obtain repeated samples from individual foraging females and complete pollen provisions from their nests. We used DNA metabarcoding based on the ITS2 locus to identify the composition of the pollen samples. We found that the composition of pollen carried on the bodies of female bees and stored in the brood provisions in their nests significantly differed among the three co-occurring species. At the intraspecific level, individual females consistently differed in their level of specialisation and in the composition of pollen carried on their bodies and stored in their nests. We also demonstrate that higher generalisation at the species level stemmed from larger among-individual variation in diets, as observed in other types of consumers, such as predators. Our study thus reveals how specialisation and foraging preferences of bees change from the scale of individual foraging bouts to complete pollen provisions accumulated in their nests over many days. Such a multi-scale view of foraging behaviour is necessary to improve our understanding of the functioning of plant-flower visitor communities.
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Affiliation(s)
- Jan Klečka
- Institute of Entomology, Biology Centre of the Czech Academy of Sciences, České Budějovice, Czech Republic
| | - Michael Mikát
- Department of Zoology, Faculty of Science, Charles University, Prague, Czech Republic
| | - Pavla Koloušková
- Institute of Entomology, Biology Centre of the Czech Academy of Sciences, České Budějovice, Czech Republic
| | - Jiří Hadrava
- Institute of Entomology, Biology Centre of the Czech Academy of Sciences, České Budějovice, Czech Republic,Department of Zoology, Faculty of Science, Charles University, Prague, Czech Republic
| | - Jakub Straka
- Department of Zoology, Faculty of Science, Charles University, Prague, Czech Republic
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Dorchin A, Shafir A, Neumann FH, Langgut D, Vereecken NJ, Mayrose I. Bee flowers drive macroevolutionary diversification in long-horned bees. Proc Biol Sci 2021; 288:20210533. [PMID: 34547912 PMCID: PMC8515878 DOI: 10.1098/rspb.2021.0533] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The role of plant–pollinator interactions in the rapid radiation of the angiosperms have long fascinated evolutionary biologists. Studies have brought evidence for pollinator-driven diversification of various plant lineages, particularly plants with specialized flowers and concealed rewards. By contrast, little is known about how this crucial interaction has shaped macroevolutionary patterns of floral visitors. In particular, there is currently no empirical evidence that floral host association has increased diversification in bees, the most prominent group of floral visitors that essentially rely on angiosperm pollen. In this study, we examine how floral host preference influenced diversification in eucerine bees (Apidae, Eucerini), which exhibit large variations in their floral associations. We combine quantitative pollen analyses with a recently proposed phylogenetic hypothesis, and use a state speciation and extinction probabilistic approach. Using this framework, we provide the first evidence that multiple evolutionary transitions from host plants with accessible pollen to restricted pollen from ‘bee-flowers’ have significantly increased the diversification of a bee clade. We suggest that exploiting host plants with restricted pollen has allowed the exploitation of a new ecological niche for eucerine bees and contributed both to their colonization of vast regions of the world and their rapid diversification.
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Affiliation(s)
- Achik Dorchin
- The National Natural History Collections, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Jerusalem 9190401, Israel
| | - Anat Shafir
- School of Plant Sciences and Food Security, George S. Wise Faculty of Life Sciences, The Edmond J. Safra Center for Bioinformatics, Tel Aviv University, Tel Aviv 69978, Israel
| | - Frank H Neumann
- Evolutionary Studies Institute, University of the Witwatersrand, Braamfontein 2050, Johannesburg, South Africa
| | - Dafna Langgut
- Department of Archaeology and Ancient Near Eastern Cultures, and The Steinhardt Museum of Natural History, Tel Aviv University, Israel
| | | | - Itay Mayrose
- School of Plant Sciences and Food Security, George S. Wise Faculty of Life Sciences, The Edmond J. Safra Center for Bioinformatics, Tel Aviv University, Tel Aviv 69978, Israel
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Sculfort O, Gérard M, Gekière A, Nonclercq D, Gerbaux P, Duez P, Vanderplanck M. Specialized Metabolites in Floral Resources: Effects and Detection in Buff-Tailed Bumblebees. Front Ecol Evol 2021. [DOI: 10.3389/fevo.2021.669352] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The selection of appropriate food resources by bees is a critical aspect for the maintenance of their populations, especially in the current context of global change and pollinator decline. Wild bees have a sophisticated ability to forage selectively on specific resources, and can assess the quality of pollen using contact chemosensory perception (taste). While numerous studies have investigated the detection of pollen macronutrients in bees and their impact on bee health and reproductive success, only a few studies have described the gustatory responses of bees toward specialized metabolites. In addition, these studies mostly focused on the response to nectar and neglected pollen, which is the main food resource for both bee imagines and larvae. Whether bees have the ability to detect specialized toxic metabolites in pollen and then rapidly adapt their foraging behavior to avoid them is very little studied. In this study, we tested whether pollen specialized metabolites affect bumblebees at both the micro-colony and individual levels (i.e., bioassays using supplemented pollen), and whether foragers detect these specialized metabolites and potentially display an avoidance behavior (i.e., preference tests using supplemented syrup). Bumblebees were fed with either amygdalin-, scopolamine- or sinigrin-supplemented pollen diets in ratios that mimic 50%, 100%, and 200% of naturally occurring concentrations. We found no effect of these specialized metabolites on resource collection, reproductive success and stress response at the micro-colony level. At the individual level, bumblebees fed on 50%-amygdalin or 50%-scopolamine diets displayed the highest scores for damage to their digestive systems. Interestingly, during the preference tests, the solution with 50%-scopolamine displayed a phagostimulatory activity, whereas solution with 50%-amygdalin had a deterrent effect and could trigger an active avoidance behavior in bumblebees, with a faster proboscis retraction. Our results suggest that regulation of toxin intake is not as well-established and effective as the regulation of nutrient intake in bees. Bees are therefore not equally adapted to all specialized pollen metabolites that they can come into contact with.
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Cane JH, Gardner DR, Weber M. Neurotoxic alkaloid in pollen and nectar excludes generalist bees from foraging at death-camas, Toxicoscordion paniculatum (Melanthiaceae). Biol J Linn Soc Lond 2020. [DOI: 10.1093/biolinnean/blaa159] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Abstract
Abstract
Many plants produce broadly active toxins to which specialist herbivores—typically insects—have evolved counter-adaptations, sometimes spawning co-evolutionary arms races. Many non-social bee species are likewise taxonomic host specialists, but the specialists’ pollen hosts frequently attract diverse floral generalists as well, even to flowers of plants that are otherwise chemically defended. In this study of foothills death-camas, Toxicoscordion paniculatum (Nutt.) Rydberg (formerly Zigadenus), we show that its pollen and nectar both contain zygacine, the steroidal alkaloid responsible for this plant’s notorious mammalian toxicity. Hungry naïve adults of a generalist solitary bee, Osmia lignaria Say (Megachilidae), would briefly drink death-camas nectar or biologically relevant doses of zygacine in syrup, followed by prolonged bouts of irritable tongue grooming; many became paralyzed and some even died. Larvae fed dosed provision masses likewise often ceased feeding and sometimes died. Prolonged irritation and subsequent deterrence of foraging O. lignaria likely illustrates why it and 50+ other vernal bee species were absent from death-camas flowers in a five-state survey. The sole visiting bee, Andrena astragali, foraged exclusively at death-camas flowers for pollen and nectar. Thus, a toxic alkaloid found in death-camas pollen and nectar deters generalist bees from flowers of this pollinator-dependent monocot, restricting visitation to a single specialist bee that tolerates death-camas toxins and is its likely pollinator.
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Affiliation(s)
- James H Cane
- USDA-ARS, Pollinating Insect Research Unit, Logan, UT, USA
| | - Dale R Gardner
- USDA-ARS, Poisonous Plant Research Laboratory, Logan, UT, USA
| | - Melissa Weber
- USDA-ARS, Pollinating Insect Research Unit, Logan, UT, USA
- Biology Department, Utah State University, Logan, UT, USA
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