Pollen Host Research Articles

Better safe than sorry? A Fabaceae species exhibits unfavourable pollen properties for developing bee larvae despite its hidden anthers

Empirical evidence suggests that pollen chemistry plays an important role in shaping the pollen host spectra of many bee species. Although the underlying mechanisms are poorly understood, pollen diets of several plant taxa have experimentally been found to impede larval development of unspecialized bees. The pollen of all plant taxa, for which such a detrimental effect on bee larval development has been observed so far, is freely accessible in the flowers and thus easily harvestable for flower visitors, suggesting that this pollen might be chemically protected in order to reduce its loss to pollen-feeding animals. In the present study, we compared larval performance of five solitary bee species on pollen diets of the two Fabaceae species Onobrychis viciifolia and Lotus corniculatus, which have their anthers concealed inside the flowers, with that on control diets composed of host pollen provisions. As the complex flower morphology of the two Fabaceae species already considerably narrows the spectrum of pollen harvesting bee taxa, which might supersede costly chemical protection of the pollen, we expected bees that usually do not exploit Fabaceae to develop well on Onobrychis and Lotus pollen diets. Larval survival on the Onobrychis pollen diet was successful for all five bee species tested. In contrast, larval survival on the Lotus pollen diet was reduced in three species despite the fact that Lotus flowers are more difficult to exploit for pollen than Onobrychis flowers. We conclude that there is no trade-off between pollen concealment and pollen defence in Lotus and that pollen of morphologically complex flowers with a restricted visitor spectrum is not necessarily an easy-to-use nutritional source.

Palaearctic Hoplitis bees of the subgenera Chlidoplitis and Megahoplitis (Megachilidae, Osmiini): biology, taxonomy and key to species.

Chlidoplitis and Megahoplitis are closely related Palaearctic subgenera of the osmiine bee genus Hoplitis (Megachilidae) containing nine and two species, respectively. Analysis of female pollen loads and field observations suggest that all species are pollen specialists. Whereas the H. (Chlidoplitis) species are probably all narrowly oligolectic and exclusively collect pollen on Allium (Alliaceae), Haplophyllum (Rutaceae), Reseda (Resedaceae), Teucrium (Lamiaceae), Trifolium (Fabaceae) or Hedysareae (Fabaceae), the H. (Megahoplitis) species show a close affinity to Carduoideae (Asteraceae) as pollen hosts. The few data available suggest that the H. (Chlidoplitis) species nest in preexisting insect burrows in the ground and use either chewed leaves or mud as nesting material. The nesting biology of the subgenus Megahoplitis remains unknown. The taxonomic revision of the subgenera Chlidoplitis and Megahoplitis revealed the existence of two undescribed species: H. (Chlidoplitis) haplophylli spec. nov. from southeastern Central Asia and Hoplitis (Chlidoplitis) allii spec. nov. from the Levant. Identification keys for the species of both subgenera are given including the hitherto unknown male of H. (Megahoplitis) bombiformis.

Palaearctic osmiine bees of the genera Hofferia and Stenoheriades (Megachilidae, Osmiini): biology, taxonomy and key to species.

Hofferia and Stenoheriades are closely related, species-poor genera of the osmiine bees (Megachilidae). Analysis of female pollen loads and field observations indicate that species of both genera have a strong affinity to Asteraceae as pollen hosts. Both genera use insect burrows in dead wood as nesting site, and Hofferia schmiedeknechti was found to build cell walls and nest plug with resin partly mixed with small pebbles. The taxonomic revision of the Palaearctic Hofferia and Stenoheriades species revealed the existence of a still undescribed species in the Levant, Stenoheriades levantica spec. nov.. Stenoheriades hofferi (Tkalců, 1984) is synonymized with S. coelostoma (Benoist, 1935), which is distinct from S. asiatica (Friese, 1921), and Heriades integra Benoist, 1934, formerly considered a Stenoheriades species, is synonymized with Osmia (Hoplosmia) scutellaris Morawitz, 1868. Keys for the delimitation of Hofferia and Stenoheriades from the other Palaearctic osmiine bee genera and for the identification of the Palaearctic species are given.

A tight relationship between the solitary bee <i>Calliopsis (Ceroliopoeum) laeta</i> (Andrenidae, Panurginae) and <i>Prosopis</i> pollen hosts (Fabaceae, Mimosoideae) in xeric South American woodlands

The large genus Calliopsis (Andrenidae, Panurginae) is composed of ten subgenera with polylectic and presumably oligolectic species. These categories have been mainly developed from floral visits of female bees collecting pollen. In the present study, pollen analyses of nest provisions and scopal loads from museum specimens of the monotypic subgenus Ceroliopoeum were carried out to assess its degree of specialization to pollen host-plants. Despite the great variability of floral resources close to two active nest aggregations in the Chaco sites (83 and 44 melittophilous taxa from 36 and 17 families, respectively), the only host-plant recorded in all nest pollen samples was Prosopis. This genus was represented by six species and their hybrids, all having similar pollen morphology. The nesting sites in Monte scrub also contained several Prosopis species, some of which had different pollen morphology from those of the Chaco forest. Two different Prosopis pollen types were identified in all samples. Since the whole geographic distribution of C. laeta matches with the range of Prosopis, its strong association with this pollen host seems to be well supported. However, the low number of study populations (four) could erroneously indicate oligolectism. A broader sampling is necessary to ensure the character of specialization. Most Calliopsis species have been identified as oligolectic. Yet, this categorization has mainly been based on floral visits and a large diversity of floral hosts has been recorded for each bee species. Further analyses are necessary to confirm the relationship of this genus with its pollen hosts. Moreover, as most of them have short to medium phenologies (up to 4 months) their presumably oligolecty can be due to a local specialization (i.e. variable according to location) typical of polylecty.

The oligolecty status of a specialist bee of South American Prosopis (Fabaceae) supported by pollen analysis and floral visitation methods

Despite the nest pollen provisions in Western Argentina are composed only of Prosopis, the fact that the ground-nesting bee Eremapis parvula visits several floral hosts suggested that it is a generalist bee species. In the South American Dry Chaco forest, seven nest aggregations of E. parvula were found during three different spring periods. From 34 to 73 species of floral hosts were recorded around each nest aggregation. However, all nest pollen samples were composed of Prosopis pollen alone, as previously found in nests from Western Argentina. Thus, pollen analysis proved that E. parvula is a specialist bee of Prosopis. The “monolecty” and “narrow oligolecty” pollen specialization categories cannot be differentiated using pollen analysis alone. For this reason, a complementary floral visitation method was used. As several Prosopis species have been reported in floral records, the narrow oligolecty category for E. parvula is supported here. Considering that this exomalopsine is a multivoltine bee, and that flowers of some of the more than seven Prosopis species are always available during spring, synchronization between them in rainy periods is highly probable. Thus, it is unlikely that E. parvula has to forage on alternative pollen hosts.

Intra‐ and interpopulational variation in the ability of a solitary bee species to develop on non‐host pollen: implications for host range expansion

Summary Pollen host choice in bees is in many cases highly conserved, which might partly be due to physiological limitations of bee larvae to digest non‐host pollen. These limitations need to be overcome in order to incorporate new pollen hosts; however, the mechanisms underlying such host expansion are poorly understood. In this study, we examined intra‐ and interpopulational variation in the ability of larvae of the solitary bee species Osmia cornuta (Megachilidae) to develop on a non‐host pollen diet of Ranunculus acris (Ranunculaceae) by comparing larval performance within and between five geographically distant European populations. The majority of bee larvae from all tested populations died when reared on the Ranunculus pollen diet. Between 10% and 43·5% of all larvae per population reached the cocoon stage, and 48% of these emerged as viable adults from the cocoons, indicating that the physiological ability to cope with the unfavourable properties of Ranunculus pollen exists in each population. The bee larvae of one population exhibited significantly reduced survival on the Ranunculus pollen diet compared with three of the four other populations. Although bees that successfully developed on the Ranunculus pollen diet showed a distinctly prolonged development time, exhibited higher mortality during diapause and reached a considerably lower adult weight compared with individuals fed the control pollen diet, several of the Ranunculus fed individuals were able to reproduce and to sire viable offspring. This study provides the first evidence for both intra‐ and interpopulational variation in the physiological ability of solitary bees to digest non‐host pollen. This variation might enable host expansion and subsequent host shifts in response to natural selection.

Host range evolution in a selected group of osmiine bees (Hymenoptera: Megachilidae): the Boraginaceae-Fabaceae paradox

Bees are extraordinarily diverse with respect to host plant choice and adaptation. Recent findings suggest that bee host range might be largely governed by evolutionary constraints related to pollen digestion or flower recognition and handling. In the present study, we applied phylogenetic inference to investigate whether such constraints underlie host plant choice in bees of the Annosmia-Hoplitis group (Megachilidae) and to what extent these bees have evolved specialized adaptations for pollen collection. We demonstrate that most pollen specialist species exclusively exploit either Boraginaceae or Fabaceae, whereas all pollen generalists harvest pollen from both Boraginaceae and Fabaceae. The counterintuitive affinity towards these two plant families, which are neither closely related nor share similar flower morphologies, demonstrates that pollen host choice is considerably constrained in this group of bees. We hypothesize that this Boraginaceae-Fabaceae paradox might be the result of (1) similar secondary metabolites in the pollen of both families; (2) metabolites that can be detoxified by the same physiological tools; or (3) similar pollen nutrient composition. Contrary to the widely held belief that specialized adaptations for pollen collection are rare among bees, such adaptations are common in the Annosmia-Hoplitis bees, where they have evolved several times independently to exploit flowers of widely different morphologies.

Chemical cues involved in the attraction of the oligolectic bee Hoplitis adunca to its host plant Echium vulgare

Host recognition is a key process in oligolectic bees but the mechanisms through which they find and recognize appropriate pollen host plant are not entirely clear. Hoplitis adunca is a monolectic bee collecting pollen only from Echium spp. (Boraginaceae). We aimed to test whether Echium vulgare floral scent plays a major role in the attraction of H. adunca females, and to identify components of E. vulgare scent that may be involved in this specific attraction. We used a combination of behavioral and chemical (GC/GC–MS, PTR-MS) analyses. In order to identify the chemical cues likely to be involved in the specific attraction of H. adunca, we compared the scent of fresh flowers, nectar, pollen, and whole plants of E. vulgare and Anchusa officinalis, another Boraginaceae, which does not attract H. adunca. H. adunca females were attracted to the scent of E. vulgare flowers when offered against a blank or against the scent of A. officinalis flowers. However, H. adunca females were not attracted to the scent of A. officinalis flowers when offered against a blank. The emission spectra of the two plant species differed markedly, as did the emission spectra of various flower components (pollen, nectar and whole flowers) within a species. Pollen presented a low volatile release, but emitted significantly higher amounts of mass 55 (butanal, 1,3-butadiene, or other volatiles of molecular mass 54), and mass 83 (hexanal, hexenols, hexenyl acetate, or other volatiles of molecular mass 82) in E. vulgare than in A. officinalis. Nectar produced a particular emission spectrum with high emission rates of masses 109 and 123. Mass 109 may likely correspond to 1,4-benzoquinone, a volatile specifically measured in E. vulgare in parallel studies to this one. The flower emission spectrum was mainly a combination of the pollen and the nectar scents, although it also contained additional volatile compounds such as those of mass 63 or mass 81. As for terpenes, E. vulgare emitted limonene, longicyclene, junipene, trans-caryophyllene and α-humulene, that were not detected in A. officinalis, and the most emitted monoterpenes were α-pinene, junipene and limonene whereas the most emitted terpenoid by A. officinalis was α-pinene. After identifying these chemical cues, olfactory/behavioural assays with specific volatiles and combinations of volatiles are necessary to understand the chemical interactions of the H. adunca-E. vulgare system.

Specialist Osmia bees forage indiscriminately among hybridizing Balsamorhiza floral hosts

Pollinators, even floral generalists (=polyleges), typically specialize during individual foraging bouts, infrequently switching between floral hosts. Such transient floral constancy restricts pollen flow, and thereby gene flow, to conspecific flowers in mixed plant communities. Where incipient flowering species meet, however, weak cross-fertility and often similar floral traits can yield mixed reproductive outcomes among pollinator-dependent species. In these cases, floral constancy by polyleges sometimes serves as an ethological mating barrier. More often, their foraging infidelities instead facilitate host introgression and hybridization. Many other bee species are oligolectic (taxonomic specialists for pollen). Oligoleges could be more discriminating connoisseurs than polyleges when foraging among their limited set of related floral hosts. If true, greater foraging constancy might ensue, contributing to positive assortative mating and disruptive selection, thereby facilitating speciation among their interfertile floral hosts. To test this Connoisseur Hypothesis, nesting females of two species of oligolectic Osmia bees were presented with randomized mixed arrays of flowers of two sympatric species of their pollen host, Balsamorhiza, a genus known for hybridization. In a closely spaced grid, the females of both species preferred the larger flowered B. macrophylla, evidence for discrimination. However, both species' females showed no floral constancy whatsoever during their individual foraging bouts, switching randomly between species proportional to their floral preference. In a wider spaced array in which the bouquets reflected natural plant spacing, foraging oligolectic bees often transferred pollen surrogates (fluorescent powders) both between conspecific flowers (geitonogamy and xenogamy) and between the two Balsamorhiza species. The Connoisseur Hypothesis was therefore rejected. Foraging infidelity by these oligolectic Osmia bees will contribute to introgression and hybridization where interfertile species of Balsamorhiza meet and flower together. A literature review reveals that other plant genera whose species hybridize also attract numerous oligolectic bees, providing independent opportunities to test the generality of this conclusion.

Pollen Preference forPsychotria sp. is Not Learned in the Passion Flower Butterfly,Heliconius erato

Heliconius butterflies are known to maximize fitness by feeding on pollen from Gurania sp. and Psiguria sp. (Cucurbitales: Curcurbitaceae), and Psychotria sp. (Gentianales: Rubiaceae). This specialization involves specific physical, physiological, and behavioral adaptations including efficient search strategies in the forest to locate pollen host plants, pollen removal, and pollen external digestion. Reducing pollen host plant search time is crucial to out-compete other flower visitors and to reduce exposure to predators. One way in which this can be achieved is by using chemical cues to learn from experienced foragers in roosting aggregations. Similar strategies have been documented in bumblebees, where inexperienced individuals learn floral odors from experienced foragers. Behavioral experiments using plants preferred by Heliconius erato suggest that pollen preference in H. erato is an innate trait and consequently learning of chemical cues at roosting aggregations is unlikely.

Searching for a Manageable Pollinator for Acerola Orchards: The Solitary Oil-Collecting Bee <I>Centris analis</I> (Hymenoptera: Apidae: Centridini)

Acerola (Malpighia emarginata DC; Malpighiaceae) is an important fruit crop in Brazil. Among its pollinators, Centris (Heterocentris) analis (F.) stands out due to its abundance at flowers and prompt acceptance of trap-nests. For the first time, we propose the commercial use of Centris bees as orchard pollinators. To develop protocols for rearing and management of these bees, we analyzed trap-nest acceptance, brood-cell construction, and larval diet in Acerola orchards. Although Centris species, in general, use numerous pollen host plants, females of C. analis showed remarkable flower fidelity to Acerola for pollen supply when nesting in the orchard. Such fidelity was previously expected only for floral oil collection. The ease of acceptance of trap-nests by females of C. analis, their prolonged yearly activity period, multivoltine life history, and high pollinator efficiency characterize C. analis as an excellent potentially manageable pollinator in Acerola orchards.

Pollen hosts of western palaearctic bees of the genus Colletes (Hymenoptera: Colletidae): the Asteraceae paradox

To assess the pollen hosts of 60 western palaearctic bee species of the genus Colletes (Colletidae), we microscopically analysed 1336 pollen loads of collected females. Twenty-six species (43.3%) were found to be specialized at the level of plant family, subfamily or genus. Thirty-four species (56.7%) proved to be pollen generalists to varying degrees, visiting the flowers of up to 15 different plant families. Flowers of the subfamily Asteroideae (Asteraceae) are by far the most important pollen source, contributing 23.6% to the pollen-plant spectrum of the whole bee genus. The high significance of Asteroideae pollen is due to the large number of specialists: 14 Colletes species belonging to four different taxonomic groups harvest pollen exclusively or predominantly on flowers of the Asteroideae. By striking contrast, Asteroideae pollen plays only a marginal role in the diets of the pollen generalists: it was recorded in only 2.7% of the pollen loads and in seven out of the 34 pollen generalists. Among the few generalists exploiting Asteroideae for pollen, three closely related species have ancestors which were possibly specialized on Asteraceae. The pattern of use of Asteroideae pollen by the Colletes bees supports recent findings that this pollen possesses unfavourable or protective properties, which render its digestion difficult, and suggests that bees need physiological adaptations to successfully utilize it.

Antennal responses of an oligolectic bee and its cleptoparasite to plant volatiles

Cleptoparasitic or cuckoo bees lay their eggs in nests of other bees, and the parasitic larvae feed the food that had been provided for the host larvae. Nothing is known about the specific signals used by the cuckoo bees for host nest finding, but previous studies have shown that olfactory cues originating from the host bee alone, or the host bee and the larval provision are essential. Here, I compared by using gas chromatography coupled to electroantennographic detection (GC-EAD) the antennal responses of the oligolectic oil-bee Macropis fulvipes and their cleptoparasite, Epeoloides coecutiens, to dynamic headspace scent samples of Lysimachia punctata, a pollen and oil host of Macropis. Both bee species respond to some scent compounds emitted by L. punctata, and two compounds, which were also found in scent samples collected from a Macropis nest entrance, elicited clear signals in the antennae of both species. These compounds may not only play a role for host plant detection by Macropis, but also for host nest detection by Epeoloides. I hypothesise that oligolectic bees and their cleptoparasites use the same compounds for host plant and host nest detection, respectively.

Phylogeny and host-plant evolution in Melittidaes.l.(Hymenoptera: Apoidea)

Bees and the angiosperms they pollinate have developed intimate and often complex interactions over the past 100 million years. As in other insect-plant interactions, host-plant specificity is variable among taxa. While many solitary bee species display an obvious preference for a narrow spectrum of host-plants (oligolecty), others regularly visit a diversified array of pollen hosts (polylecty). Few studies have examined the patterns of host-plant associations in bees using well-resolved phylogenies at the species level combined with accurate and quantitative data on host-plant preferences. In this study, we examined the evolution of bee-plant relationships in several genera of specialist (oligolectic) bees. We used the Melittidae s.l. as a model taxon by mapping the preferred pollen hosts onto species-level phylogenies to investigate the frequency and pattern of host-plant switching. Our results suggest that host-plant associations are maintained over time in many lineages, but that host switches to unrelated plant families are also common. We find some evidence that host-switches occur more frequently to morphologically similar, rather than closely-related, host-plants suggesting that floral morphology plays a key role in host-plant evolution in bees.

Phylogeny of the Callandrena subgenus of Andrena (Hymenoptera: Andrenidae) based on mitochondrial and nuclear DNA data: Polyphyly and convergent evolution

We propose a phylogenetic hypothesis of relationships within Callandrena, a North American subgenus of the bee genus Andrena, based on both mitochondrial and nuclear DNA sequences. Our data included 695 aligned base pairs comprising parts of the mitochondrial genes cytochrome oxidase subunits I and II and the intervening tRNA-leucine and 767 aligned base pairs of the F2 copy of the nuclear gene elongation factor-1α. We also suggest a preliminary hypothesis of relationships of the North American subgenera in the genus. Our analyses included 54 species of Callandrena, 42 species of Andrena representing 24 additional subgenera, and 11 outgroup species in the family Andrenidae. Parsimony analyses of each marker separately suggested that Callandrena was polyphyletic, with a combined analysis suggesting that there were at least two phylogenetically independent clades of bees with similar morphological features. Maximum likelihood and Bayesian analyses supported this conclusion, as did the non-parametric bootstrapping SOWH test. Convergence in morphological characters was likely due to their common use of members of Asteraceae as pollen hosts.

Resource Use and Nesting Behavior of Megachile prosopidis and M. chilopsidis with Notes on M. discorhina (Hymenoptera: Megachilidae)

The nesting behavior of Megachile prosopidis Cockerell, Megachile chilopsidis Cockerell, and Megachile discorhina Cockerell was studied in trap nests placed near Tucson, Arizona. Quantitative differences among the five distinct nest plugs made by M. prosopidis are described. The nest plugs fall into three structural types. The first layer of capping material deposited in the first structural type is sand and an unidentified oral secretion mixed to form a hard layer. In the second structural type, the first layer is made of soft resin mixed with sand or organic matter. A third, less common, structural type includes those nests capped with pure resin. The dominant pollen host plant species was identified as Cercidium microphyllum (Torr.) Rose and Johnston (Fabaceae). Two other legumes, Prosopis velutina Wooton and Olneya tesota A. Gray, became important pollen sources late in the nesting season. Resin samples taken from the nest caps were indistinguishable, by gas chromatography, from resin of Encelia farinosa A. Gray (Asteraceae). The following parasites and predators were reared from the nests: Tricrania stansburyi Haldeman (Coleoptera: Meloidae), Lecontella gnara Wolcott (Coleoptera: Cleridae), Anthrax cintalpa Cole (Diptera: Bombyliidae), Stelis (Dolichostelis) perpulchra Crawford (Hymenoptera: Megachilidae), and Sapyga sp. Latreille (Hymenoptera: Sapygidae). New host records are reported for T. stansburyi, L. gnara, and A. cintalpa.

Character analysis of adaptations for tarsal pollen collection in the Bombyliidae (Insecta: Diptera): the benefits of putting your foot in your mouth

Using direct observations and analyses of gut contents, we document that pollen feeding is widespread among female bombyliid flies. Pollen feeding is typically indirect with the initial pollen acquisition accomplished by foretarsal stroking of the anthers. Observations of the foretarsi using light and scanning electron microscopy showed that the foretarsi bear modified setae that play a role in pollen collection. Across the family, we found considerable variation in the morphology and distribution of the foretarsal setae that appear to be more related to phylogeny than pollen host. The major patterns of foretarsal setal specialization are illustrated and discussed.

Use of novel pollen species by specialist and generalist solitary bees (Hymenoptera: Megachilidae)

If trade-offs between flexibility to use a range of host species and efficiency on a limited set underlie the evolution of diet breadth, one resulting prediction is that specialists ought to be more restricted than generalists in their ability to use novel resource species. I used foraging tests and feeding trials to compare the ability of a generalist and a specialist solitary mason bee species to collect and develop on two pollen species that are not normally used in natural populations (novel pollens). Osmia lignaria (Hymenoptera: Megachilidae) is a generalist pollen feeder; O. californica, is more specialized. Adults of the specialist were more limited in use of novel hosts, but only in some contexts. Both bee species refused to collect one novel pollen. The specialist accepted a second novel pollen only when it was presented along with its normal pollen, whereas the generalist collected novel pollen whether presented alone or with normal pollen. Surprisingly, larvae of the specialist were more flexible than were generalists. The specialist grew well on mixtures of normal and novel pollen species, in some cases better than on its normal host alone. Larvae of the generalist grew more poorly on all diets containing novel pollens than on their normal host. Data on these two species of bees suggest that specialization by itself need not reduce flexibility on novel hosts. The findings also provide information about mechanisms of specialization in bees. Similar to some folivores, specific cues of the pollen host and the bee's interpretation of these contribute, along with foraging economics, to pollen choice by adults. The ability of the larvae to cope with specific components of one pollen species need not interfere with its ability to use others.

Pollinator genetics and pollination: do honey bee colonies selected for pollen‐hoarding field better pollinators of cranberry Vaccinium macrocarpon?

Summary1. Genetic polymorphisms of flowering plants can influence pollinator foraging but it is not known whether heritable foraging polymorphisms of pollinators influence their pollination efficacies. Honey bees Apis mellifera L. visit cranberry flowers for nectar but rarely for pollen when alternative preferred flowers grow nearby.2. Cranberry flowers visited once by pollen‐foraging honey bees received four‐fold more stigmatic pollen than flowers visited by mere nectar‐foragers (excluding nectar thieves). Manual greenhouse pollinations with fixed numbers of pollen tetrads (0, 2, 4, 8, 16, 32) achieved maximal fruit set with just eight pollen tetrads. Pollen‐foraging honey bees yielded a calculated 63% more berries than equal numbers of non‐thieving nectar‐foragers, even though both classes of forager made stigmatic contact.3. Colonies headed by queens of a pollen‐hoarding genotype fielded significantly more pollen‐foraging trips than standard commercial genotypes, as did hives fitted with permanently engaged pollen traps or colonies containing more larvae. Pollen‐hoarding colonies together brought back twice as many cranberry pollen loads as control colonies, which was marginally significant despite marked daily variation in the proportion of collected pollen that was cranberry.4. Caloric supplementation of matched, paired colonies failed to enhance pollen foraging despite the meagre nectar yields of individual cranberry flowers.5. Heritable behavioural polymorphisms of the honey bee, such as pollen‐hoarding, can enhance fruit and seed set by a floral host (e.g. cranberry), but only if more preferred pollen hosts are absent or rare. Otherwise, honey bees' broad polylecty, flight range, and daily idiosyncrasies in floral fidelity will obscure specific pollen‐foraging differences at a given floral host, even among paired colonies in a seemingly uniform agricultural setting.

The Nesting Biology of Colletes kincaidii Cockerell (Hymenoptera: Colletidae) and Development of Its Immature Forms

Overwintering larvae of Colletes kincaidii Cockerell were obtained by removing soil blocks from a large nesting site established in a hardened, vertical sandstone cliff at Bonny Doon, Calif. One sandstone block was placed in a greenhouse at Logan, Utah, where two emerging females established nests within glass tubes inserted into observation boxes and one female excavated a nest in soil beneath the sandstone block from which she emerged. Observations of nesting biology in glass tube nests showed for the first time that polyester cell linings are composed of a mixture of salivary and Dufour's gland materials. Salivary secretion is first brushed onto nest walls with the glossa; Dufour's gland liquid is deposited on top of the salivary layer and brushed into a thin cover layer with the bifid glossa. The careful sequence of glandular deposition, combined with physical evidence obtained during observations, suggests that salivary gland material may carry an enzyme that links lactones derived from the Dufour's gland into polyester chains that are incorporated into cell linings. Cell platform construction and how this platform is used to position the female during the act of egg deposition are described. The physical restructuring of the platform into a cell cap immediately after the egg is deposited is also described. Cell provisioning and methods used to deposit the egg are described in detail. Late embryogenesis and immature development were observed in the laboratory using in vivo and in vitro methods. These observations confirm the 180° rotation of the embryo, eclosion from the egg chorion as a second instar, anus-to-mouth feeding habits of the larva, and the migration pattern of the larva from its position within the egg to the cup-shaped central position on the surface of the cell provisions. Supportive studies in the field confirmed that some females in a nesting population excavate their entire burrow system while others use abandoned nests and extend lateral burrows before constructing cell series in these new excavations; some females use abandoned nests to construct cell series only within the residue cell linings produced by previous generations. These studies also confirmed that any one cell of C. kincaidii is provisioned with only one pollen host species, but any number of pollen host species can be used by the same individual, different individuals, or populations that are distributed across North America; and that Epeolus compactus Cresson and Paravilla fumosa Hall were found parasitizing C. kincaidii . Much of the new information is used as a first step in establishing the evolutionary status of Colletidae.