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An animal's diet breadth is a central aspect of its life history, yet the factors determining why some species have narrow dietary breadths (specialists) and others have broad dietary breadths (generalists) remain poorly understood. This challenge is pronounced in herbivorous insects due to incomplete host plant data across many taxa and regions. Here, we develop and validate machine learning models to predict pollen diet breadth in bees, using a bee phylogeny and occurrence data for 682 bee species native to the United States, aiming to better understand key drivers. We found that pollen specialist bees made an average of 72.9% of their visits to host plants and could be predicted with high accuracy (mean 94%). Our models predicted generalist bee species, which made up a minority of the species in our dataset, with lower accuracy (mean 70%). The models tested on spatially and phylogenetically blocked data revealed that the most informative predictors of diet breadth are plant phylogenetic diversity, bee species' geographic range, and regional abundance. Our findings also confirm that range size is predictive of diet breadth and that both male and female specialist bees mostly visit their host plants. Overall, our results suggest we can use visitation data to predict specialist bee species in regions and for taxonomic groups where diet breadth is unknown, though predicting generalists may be more challenging. These methods can thus enhance our understanding of plant-pollinator interactions, leading to improved conservation outcomes and a better understanding of the pollination services bees provide.

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.

Mimocolletes apiculus gen. nov. and sp. nov. is described from south-western Australia. Based on morphology, this bee's closest affinities are deemed to lie with the genus Glossurocolletes Michener. Like the two species of that genus, M. apiculus appears to be oligolectic on certain pea-flowered plants (mirbelioid Fabaceae) and exhibits some morphological adaptations in common with various other colletid bees that favour pea flowers. In particular, the proboscis is slender with a strongly compressed prementum and extended glossa. [ABSTRACT FROM AUTHOR]

Anthophora onosmarum is a poorly known bee species described from the Caucasus (Georgia). New fieldwork has revealed that the species is present in Bulgaria and Greece, and is also widespread across Turkey, predominantly on the Anatolian plateau. New behavioural data shows that A. onosmarum is likely narrowly oligolectic on the plant genus Onosma (Boraginaceae), and is capable of buzzing flowers to release pollen. This finding illustrates the growing trend of overlooked bee species with more Caucasian, Anatolian, or even Middle Eastern distributions occurring in under-surveyed mountainous parts of the Southern Balkans. [ABSTRACT FROM AUTHOR]

North-western Africa has a large Andrena fauna, but parts of the country away from coastal areas remain poorly studied, and confusion persists as to the identity of certain taxa due to the long history of study combined with imperfectly examined type material. New fieldwork, genetic barcoding, and study of museum material has substantially improved our understanding of this region. Eleven new species are described: A. (Aciandrena) bendai sp. nov., A. (Aciandrena) ifranensis sp. nov., A. (Euandrena) berberica sp. nov., A. (Hoplandrena) darha sp. nov., A. (Micrandrena) anammas sp. nov., A. (Micrandrena) gemina sp. nov., A. (Micrandrena) tinctoria sp. nov., and A. (incertae sedis) muelleri sp. nov., all from Morocco, and A. (Aciandrena) quieta sp. nov., A. (Euandrena) abscondita sp. nov., and A. (Taeniandrena) prazi sp. nov. from Morocco and Tunisia. Andrena (Aciandrena) nitidilabris Pérez, 1895 was misdiagnosed, and is actually the senior synonym of A. (Graecandrena) montarca parva Warncke, 1974 syn. nov. Andrena (Aciandrena) pisantyi sp. nov. is described from Algeria, Tunisia, and Israel, conforming to A. nitidilabris auctorum sensu Warncke. Andrena (Graecandrena) andina Warncke, 1974 stat. nov. and A. (Micrandrena) heliaca Warncke, 1974 stat. nov. are elevated from sub species to species status. Lectotypes are designated for A. (Melanapis) ephippium Spinola, 1838, A. (Melanapis) rutila Spinola, 1838, A. (Simandrena) rhypara Pérez, 1903, and A. (Suandrena) savignyi Spinola, 1838. Neotypes are designated for A. (Melandrena) soror Dours, 1872 and A. (Notandrena) nigroviridula Dours, 1873. The female of A. (Aciandrena) triangulivalvis Wood, 2020 is described. The following seven additional synonymies are reported (senior name first): A. (Chrysandrena) testaceipes Saunders, 1908 = A. (Chrysandrena) rubricorpora Wood, 2021 syn. nov., A. (incertae sedis) maidaqi Scheuchl & Gusenleitner, 2007 = A. (Carandrena) hoggara Wood, 2021 syn. nov., A. (Lepidandrena) tuberculifera Pérez, 1895 = A. (Poecilandrena) nigriclypeus Wood, 2020 syn. nov., A. (Notandrena) albohirta Saunders, 1908 = A. (Notandrena) eddaensis Gusenleitner, 1998 syn. nov., A. (Notandrena) microthorax Pérez, 1895 = A. (Notandrena) nigrocyanea Saunders, 1908 syn. nov., A. (Simandrena) rhypara = A. (Simandrena) palumba Warncke, 1974 syn. nov., and A. (Taeniandrena) poupillieri Dours, 1872 = A. (Taeniandrena) lecerfi Benoist, 1961 syn. nov. Andrena (Notandrena) viridiaenea Pérez, 1903 is returned to synonymy with A. nigroviridula. Relative to the 2020 baseline, 16 Andrena species are newly recorded for Morocco, and six species are removed from the faunal list. These revisions bring the total number of Andrena species known from Morocco to 202 with 25 endemic species, making it one of the hotspots for Andrena diversity globally.

Specialist insect herbivores make up a substantial fraction of Earth's biodiversity; however, they exploit a minority of plant lineages. For instance, in the eastern United States and Canada, ~25% of bee species are pollen specialists, but they are hosted by a small fraction of the native, animal‐pollinated angiosperms in the region: Only 6% of plant genera and 3% of families support pollen‐specialist bees. It is unclear why some plant lineages host specialist bees while others do not. We know that at least some specialist bees use plant taxa that are avoided by generalists, suggesting that specialist bees favor plants with low‐quality pollen, potentially as a strategy to escape competition or obtain protection from natural enemies. There is also evidence that specialist bees prefer superabundant host plants. Here we investigate whether pollen quality and plant abundance predict patterns of host use by specialist bees in eastern North America. Through field observations, we find that plants hosting specialist bees are frequent sources of pollen for generalists, suggesting that their pollen is not generally avoided by bees due to poor pollen quality. In addition, our analysis of a large citizen‐science data set shows that regional abundance strongly predicts which plant genera in the eastern United States host pollen‐specialist bees. Our results show that bees specialize on regionally abundant—but not necessarily low‐quality—plant lineages. These plant lineages may provide more opportunities for the evolution of specialists and lower likelihood of specialist extinction. [ABSTRACT FROM AUTHOR]

Species exhibit a range of specialisation in diet and other niche axes, with specialists typically thought to be more efficient in resource use but more vulnerable to extinction than generalists. Among herbivorous insects, dietary specialists seem more likely to lack acceptable host plants during the insect's feeding stage, owing to fluctuations in host‐plant abundance or phenology. Like other herbivores, bee species vary in host breadth from pollen specialisation (oligolecty) to generalisation (polylecty).Several studies have shown greater interannual variation in flowering phenology for earlier‐flowering plants than later‐flowering plants, suggesting that early‐season bees may experience substantial year‐to‐year variation in the floral taxa available to them.It was therefore reasoned that, among bees, early phenology could be a more viable strategy for generalists, which can use resources from multiple floral taxa, than for specialists. Consequently, it was expected that the median dates of collection of adult specimens to be earlier for generalist species than for specialists. To test this, phenology data and pollen diet information on 67 North American species of the bee genus Osmia was obtained.Controlling for latitude and phylogeny, it was found that dietary generalisation is associated with significantly earlier phenology, with generalists active, on average, 11–14 days earlier than specialists.This result is consistent with the generalist strategy being more viable than the specialist strategy for species active in early spring, suggesting that dietary specialisation may constrain the evolution of bee phenology—or vice versa. [ABSTRACT FROM AUTHOR]

Masked or yellow-faced bees of the genus Hylaeus (Colletidae) differ in their mode of pollen transportation from most other bees in that they ingest the pollen directly on the flowers and carry it back to the nest inside the crop located in the anterior half of the metasoma. Due to this hidden mode of pollen transportation, the examination of pollen collected by Hylaeus females requires the dissection of the metasoma. Although this method has never been applied in Europe, the great majority of the Central European Hylaeus species were supposed to be pollen generalists based on observations of flower visits. The microscopical analysis of pollen removed from 30 crops each of 36 Central European Hylaeus species revealed that the proportion of species exhibiting an exclusive or strong preference for pollen from a single plant taxon is much higher than hitherto assumed and that the current assumption of the genus Hylaeus to largely consist of pollen generalists is wrong. Nineteen of the 36 species examined are strictly or largely dependent on a single plant taxon for collecting pollen, such as Apiaceae (n = 11 species), Rosaceae (n = 3), Reseda (Resedaceae) (n = 2), Allium (Amaryllidaceae) (n = 1), Asteraceae (n = 1) and Melilotus (Fabaceae) (n = 1). The 36 Hylaeus species examined collected pollen from the flowers of 31 plant families, of which the Apiaceae and Rosaceae (particularly Potentilla and Rubus) were by far the most important contributing almost 60% to the pollen host spectrum of the entire genus. The comparison between pollen host spectrum and flower visiting records showed that the pollen generalists use the flowers of the Asteraceae as nectar rather than pollen sources, corroborating earlier findings that the digestion of Asteraceae pollen requires physiological adaptations to cope with its unfavourable or protective properties. In summary, the patterns of pollen host use by bees of the genus Hylaeus do not substantially differ from those of other Palaearctic bee taxa despite the masked bees' unusual habit to ingest the pollen directly on the flowers and to transport it inside their body back to the nest. [ABSTRACT FROM AUTHOR]

Two new species of Leioproctus (L. aureofimbriatus from eastern New South Wales and L. haemodori from south-western Australia) are described. Both species have been found only when visiting Haemodorum species that have dull brown to black flowers that do not open. The bee species are closely related to each other, but their relationship with other Leioproctus species is unclear. Both have morphological features that would assist in foraging from the flowers, males have similar terminalia and antennae with the apical segment flattened and expanded. This last feature occurs also in the distantly related species Leioproctus (Ceratocolletes) antennatus resulting in occasional misidentifications. We have not created a new subgenus for these species because of difficulties with separating phylogenetically significant features from adaptive or adventitious ones. The mutualistic association between the bees and flowers has some novel characteristics and warrants further study. [ABSTRACT FROM AUTHOR]

Solitary bees play a crucial role in ecological systems, contributing to the pollination of crops and wild plants. All females are reproductive, and their habitat requirements include nesting sites, food resources and nesting materials. Although these activities require the ability to detect biotic and abiotic stimuli in the environment, the sensory system of these species is poorly studied. In this study, the antennal sensilla of five solitary bee species belonging to three Apoidea families were investigated using scanning electron microscopy. These included two species of stem-nesting bees, Ceratina cucurbitina (Rossi, 1792) (Apidae) and Osmia scutellaris (Morawitz, 1868) (Megachilidae), and three species of ground-nesting bees, Lasioglossum brevicorne (Schenck, 1870), Lasioglossum leucozonium (Schrank, 1781), and Lasioglossum villosulum (Kirby, 1802) (Halictidae). Thirteen different types of antennal sensilla were identified in females based on their morphological characteristics: sensilla trichodea (subtypes STI, II, III), chaetica (subtypes SchI, II), basiconica (subtypes SBI, II, III, IV), placodea, campaniformia, coeloconica, and ampullacea. Their functional role was discussed and morphology was compared among the species and within the antennal segments in each species. The results provide a baseline for further physiological and behavioural studies to determine the role of antennal sensilla in habitat selection, food search and nesting site selection. • Antennal sensilla are described in females of five species of Apoidea. • Seven types of sensilla and related morphological subtypes are identified using scanning electron microscopy. • Differences in types and distribution are found among ground and stem nesting species. [ABSTRACT FROM AUTHOR]

Many bee species are dietary specialists and restrict their pollen foraging to a subset of the available flowers. However, the reasons for specialization—and the reasons certain plant taxa support numerous specialists—are often unclear. Many bees specialize on the plant family Asteraceae, despite evidence its pollen is a poor food for non-specialists. Here, we studied six mason bee (Osmia) species, including three Asteraceae specialists, to test whether observed pollen-usage patterns reflect larval nutritional requirements, to investigate what aspects of Asteraceae pollen make it unsuitable for non-specialists, and to understand how Asteraceae specialists tolerate their seemingly low-quality diet. We reared larval bees on host and nonhost pollen and found that Asteraceae specialists could develop on nonhost provisions, but that other bees could not survive on Asteraceae provisions. These effects did not seem related to nutritional deficiencies, since Asteraceae provisions were not amino acid deficient, and we found no consistent differences in digestive efficiency among pollen types. However, Asteraceae specialists completed more foraging flights per larva, generally collected relatively larger provisions, and produced more frass (waste) than the other species, suggesting quantitative compensation for low food quality. Toxins, deficiencies in unmeasured nutrients, or aspects of pollen grain structure might explain poor survival of non-specialists on Asteraceae provisions. Our results suggest that floral host selection by specialist bees is not related to optimizing larval nutrition. We recommend further investigation of host-selection behaviour in adult bees and of pollen digestion in larvae to better understand the evolution of bee–flower associations. [ABSTRACT FROM AUTHOR]

Monolecty in bees was defined a century ago for those species that consistently collect pollen only from the same single species of floral host. Even at the time, the term was considered "a curiosity" with little biological meaning. Here, I review its multiple problems and suggest that its utility would improve if we apply the term monolecty to those bees species that use a single genus (not species) of flowering host. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Bee pollen gathering from a few related plant species is a specialisation known as oligolecty. Although it is an extended phenomenon, it has been scarcely explored in oil-collecting bees. At the geographic level, there is little information about oligolecty persistence and also about phenotypic variation of bees related with abiotic factors. We studied the pollen collection specialisation of the oil-collecting bee Chalepogenus cocuccii, its pollination interactions and phenotypic variation across its distribution range, by analyses of pollen loads, field observations and morphometric measurements. Observations and pollen analyses showed that across its distribution range, C. cocuccii preferred Nierembergia flowers not only for oil but also for pollen. We found two bee-morphotypes, though phenotypic variation was not related to abiotic variables. We postulate that C. cocuccii is a narrowly oligolectic species, phenotypically and ecologically specialised in Nierembergia. [ABSTRACT FROM AUTHOR]

Heriades truncorum (Megachilidae) is a specialist bee that forages on Asteraceae and collects pollen by tapping its abdomen on pollen-presenting florets which places the grains directly in the ventral scopa. We tracked pollen transfer by female H. truncorum between conspecific inflorescences of Inula ensifolia and Pulicaria dysenterica by labelling pollen with quantum dots. On average, bees transferred 31.14 (I. ensifolia) and 9.96 (P. dysenterica) pollen grains from the last visited inflorescence, 39% and 45% of which were placed on receptive styles. Pollen germination ratio is significantly lower for inflorescences of P. dysenterica visited by one H. truncorum (0.13%) compared with open control inflorescences (0.51%), which suggests that the bees mainly transfer self-pollen of these self-incompatible plants. Thus, a single visit by H. truncorum does not grant the plant high reproductive success, but the bees' abundance and flower constancy might reduce this disadvantage. [ABSTRACT FROM AUTHOR]

The nesting behaviour of Melitoma ameghinoi was studied in the province of Chaco, Argentina. Contrary to other Melitoma species, which are known to nest on banks or other vertical or sloping surfaces, the nests were found on horizontal ground, in extremely hard clay soil. The nests were shallow, with three to four vertical cells. The short turrets pointed upwards for a short stretch and then were strongly curved, with the entrance directed towards the soil surface. The floral relationships of this species were studied by pollen analysis of faeces from cells, a pollen mass, scopal loads of specimens, and direct observation of floral visits. Pollen counts and field observations indicate that M. ameghinoi collects pollen exclusively from Ipomoea species. A compilation of pollen sources for species of Melitoma is presented. All known species, including M. ameghinoi, fall in the category of narrowly oligolectic. A discussion of the taxonomic relationships of the species is presented, and a lectotype is designated. [ABSTRACT FROM AUTHOR]

Pollen is the primary protein and nutrient source for bees and they employ many different behaviors to gather it. Numerous terms have been coined to describe pollen gathering behaviors, creating confusion as many are not clearly-defined or overlap with existing terms. There is a need for a clear yet flexible classification that enables accurate, succinct descriptions of pollen gathering behaviors to enable meaningful discussion and comparison. Here, we classify the different pollen gathering behaviors into two main classes: active and incidental pollen collection. Active pollen collection is subdivided into six behaviors: scraping with the extremities, buzzing, rubbing with the body and/or scopae, rubbing with the face, tapping, and rasping. In addition to the active and incidental pollen gathering behaviors, many bees have an intermediate step in which they temporarily accumulate pollen on a discrete patch of specialized hairs. Each behavior is described and illustrated with video examples. Many of these behaviors can be further broken down based on the variations found in different bee species. Different species or individual bees mix and match these pollen collecting behaviors depending on their behavioral plasticity and host plant morphology. Taken together, the different behaviors are combined to create complex behavioral repertoires built on a foundation of simple and basic steps. This classification sets the groundwork for further research on various topics, including behavioral plasticity in different species, comparisons between generalists and specialists, and the relative effectiveness of different pollen gathering behaviors. [ABSTRACT FROM AUTHOR]

Among associations of plants and their pollinating bees, mutually specialized pairings are rare. Typically, either pollen specialist (oligolectic) bees are joined by polylectic bees in a flowering species’ pollinator guild, or specialized flowers are pollinated by one or more polylectic bees. The bee Andrena astragali is a narrow oligolege, collecting pollen solely from two nearly identical species of death camas (Toxicoscordion, formerly Zigadenus). Neurotoxic alkaloids of these plants are implicated in sheep and honey bee poisoning. In this study, T. paniculatum, T. venenosum and co-flowering forbs were sampled for bees at 15 sites along a 900-km-long east-west transect across the northern Great Basin plus an altitudinal gradient in northern Utah’s Bear River Range. Only A. astragali bees were regularly seen visiting flowering panicles of these Toxicoscordion. In turn, this bee was never among the 170 bee species caught at 17 species of other prevalent co-occurring wildflowers in the same five state region (38,000 plants surveyed). Our field pollination experiments show that T. paniculatum is primarily an outcrosser dependent on pollinator visitation for most capsule and seed set. Thus, both A. astragali and two sister species of Toxicoscordion are narrowly specialized and co-dependent on each other for reproduction, illustrating a rare case of obligate mutual specialization in bee-plant interactions. [ABSTRACT FROM AUTHOR]

Andrena is a large genus of bees primarily distributed across the Holarctic. Despite their abundance in temperate regions, the pollen diets of many Nearctic Andrena remain incompletely resolved. The pollen diets of 50 species of Andrena found in Michigan were characterized using light microscopy. Twenty-four species (48%) were classified as pollen specialists, collecting pollen from one botanical family. The remaining 26 species (52%) were classified as pollen generalists, collecting from many botanical families. Andrena species fell into three broad foraging groups: (1) spring-flying species foraging predominantly from woody plants; (2) spring-flying species specializing on herbaceous ephemerals; and (3) summer-flying species specializing on herbaceous prairie plant species. Species of Nearctic Andrena specialized on pollens from Asteraceae, Geraniaceae, Hydrophyllaceae and Montiaceae or avoided them almost entirely. Botanical families that hosted specialized bees showed a higher variation in utilization by the Andrena community than botanical families without specialists. In contrast, Palaearctic species showed little temporal partitioning and low variation in the utilization of different botanical families. This pattern of pollen use supports previous findings that pollens from certain botanical families cannot be used as a food source without physiological adaptations, but that this phenomenon is more pronounced in the Nearctic Andrena fauna. [ABSTRACT FROM AUTHOR]

Warm temperatures are required for insect flight. Consequently, warming could benefit many high-latitude and high-altitude insects by increasing opportunities for foraging or oviposition. However, warming can also alter species interactions, including interactions with natural enemies, making the net effect of rising temperatures on population growth rate difficult to predict. We investigated the temperature-dependence of nesting activity and lifetime reproductive output over 3 yr in subalpine populations of a pollen-specialist bee, Osmia iridis. Rates of nest provisioning increased with ambient temperatures and with availability of floral resources, as expected. However, warmer conditions did not increase lifetime reproductive output. Lifetime offspring production was best explained by rates of brood parasitism (by the wasp Sapyga), which increased with temperature. Direct observations of bee and parasite activity suggest that although activity of both species is favored by warmer temperatures, bees can be active at lower ambient temperatures, while wasps are active only at higher temperatures. Thus, direct benefits to the bees of warmer temperatures were nullified by indirect costs associated with increased parasite activity. To date, most studies of climate-change effects on pollinators have focused on changing interactions between pollinators and their floral host-plants (i.e., bottom-up processes). Our results suggest that natural enemies (i.e., top-down forces) can play a key role in pollinator population regulation and should not be overlooked in forecasts of pollinator responses to climate change. [ABSTRACT FROM AUTHOR]

In this study we compare the reproductive biology of Cordia globosa and C. leucocephala (Cordiaceae, Boraginales; formerly referred to Boraginaceae) to understand the functioning of the floral morphs and the relations with their effective pollinators. The species are synchronopatric, distylic, and self-incompatible. Though they share melittophilous traits, the main visitor and pollinator of C. globosa was the generalist and exotic bee Apis mellifera, while the only one of C. leucocephala was the oligoletic bee Ceblurgus longipalpis. These two latter species are restricted to the Caatinga of NE Brazil, contrasting with the wide distribution of Cordia globosa. While the fruit-set for C. globosa was high, independently if the pollen donor/stigma receptor was a pin (long-styled) or thrum (short-styled) individual, in C. leucocephala the fruit-set was low and occurred only when a thrum individual was the pollen donor. This raises the possibility of this species moving towards dioecy. The high natural fruit-set of C. globosa confirms the generalist bee as its effective pollinator. The low fruit-set after manual crosses in C. leucocephala may be due to low pollen viability. Additionally, the low natural fruit-set (two times lower than after crosses) may be related with the foraging behavior of the specialist pollinator.Neste estudo comparamos a biologia reprodutiva de Cordia globosa e C. leucocephala para entender a função dos orfos florais e as relações com seus polinizadores efetivos. As espécies são sincronopátricas, distílicas e auto-incompatíveis. Embora elas compartilhem atributos melitófilos, o principal visitante e polinizador de C. globosa foi Apis mellifera, abelha generalista e exótica, enquanto o de C. leucocephala foi a abelha oligolética Ceblurgus longipalpis. Essas duas últimas espécies são restritas à Caatinga do Nordeste do Brasil, contrastando com a ampla distribuição de C. globosa. Enquanto a formação de frutos de C. globosa foi alta, independente se o doador ou receptor de pólen era um indivíduo brevi- ou longistilo, em C. leucocephala a formação de frutos foi baixa e ocorreu apenas quando o doador de pólen era brevistilo. Este fato levanta a possibilidade desta espécie estar se movendo em direção à dioicia. A alta formação natural de frutos de C. globosa confirma a abelha generalista como seu polinizador efetivo. A baixa formação de frutos após cruzamentos manuais e C. leucocephala pode ser devida à baixa viabilidade polínica. Adicionalmente, a baixa formação natural de frutos (duas vezes menor que a de cruzamentos) pode estar relacionada com o comportamento de forrageamento do polinizador especialista.

Se presenta información sobre la historia natural de Macrotera pipiyolin; el estudio se realizó en la Estación de Biología Chamela, Instituto de Biología, UNAM, entre junio y agosto de 1994. Las abejas emergieron poco después del inicio de la temporada de lluvias, su pico de actividad fue a principio de julio, presentando alrededor de 35 días activos. La actividad concuerda con la floración de Opuntia excelsa, planta de la que obtiene sus recursos. Las cópulas ocurren sobre las flores y los machos muestran 3 tipos de estrategias reproductivas: macho dominante, subordinado y patrullero. Las hembras son poliándricas y los machos polígamos. Las hembras construyen los nidos generalmente cerca de O. excelsa y tienen una distribución gregaria. Los nidos son simples, con un túnel principal y celdas, las que se cierran y desconectan del tunel una vez que se han aprovisionado y en ellas se ha depositado un huevo. Para la provisión de una celda se requiere de 2 a 18 cargas de polen. El desarrollo de huevo a larva adulta ocurre en 1 mes, posteriormente la larva permanece en este estado aproximadamente por 10 meses, y la pupa se presenta pocos días antes de la emergencia.Information on the natural history of Macrotera pipiyolin in the Estación de Biología Chamela (IBUNAM), based on observations made between June and August 1994 is presented. Bees emerged shortly after the rainy season; their peak of activity was in early July, with 35 days of activity. The activity of the bee is consistent with the flowering of Opuntia excelsa, the plant that provides its resources. Mating occurs on flowers, where males present 3 types of reproductive strategies: dominant, subordinate, and patrolling. Females are polyandrous and males are polygamous. Females usually build nests near O. excelsa and they have a gregarious distribution. The nests are simple with a main tunnel; after cells are provisioned with pollen and an egg is oviposited, they are closed off from the main tunnel. To provide a cell requires from 2 to 18 loads of pollen. The development from egg to larva occurs in 1 month, after which the larvae remain in this state for 10 months and the pupae appear a few days before emergence.

The pollen diet provided by adult bees to their offspring varies immensely. While some species collect pollen on several plants irrespective of their phylogenetic relatedness (polyleges), others collect only on plants within a genus or family (oligoleges). Floral scents play a central role in bee-plant interactions. To locate flowers, polyleges are assumed to rely on compounds commonly found as floral scent constituents, whereas oligoleges rely on unusual compounds to recognize host flowers unambiguously. Campanula flowers are visited by both polylectic and oligolectic species, and their scent bouquets consist of common and unusual (e.g., spiroacetals) volatiles. In a comparative approach, we performed electroantennographic analyses to investigate the antennal responses of three polyleges and three oligoleges to three common volatiles and four spiroacetals. We hypothesized that: 1) oligoleges and polyleges should respond similarly to common flower volatiles, and 2) Campanula oligoleges should be more sensitive to spiroacetals than are polyleges. In corroboration, we found that antennal sensitivity to common volatiles was similar among bees irrespective of pollen diet, whereas oligoleges of Campanula were more sensitive to spiroacetals than polyleges. Newly emerged bees of the Campanula oligolege Chelostoma rapunculi rely on spiroacetals for recognizing host-flowers, and our results suggest that this might also be true for other Campanula oligoleges, since Chelostoma campanularum and Hoplitis mitis also were able to perceive these specific volatiles at very low concentrations. Together, our results provide interesting insights into the significance of olfactory adaptations in oligolectic and polylectic bee species. [ABSTRACT FROM AUTHOR]

Healthy plant communities of the American sagebrush steppe consist of mostly wind-pollinated shrubs and grasses interspersed with a diverse mix of mostly spring-blooming, herbaceous perennial wildflowers. Native, nonsocial bees are their common floral visitors, but their floral associations and abundances are poorly known. Extrapolating from the few available pollination studies, bees are the primary pollinators needed for seed production. Bees, therefore, will underpin the success of ambitious seeding efforts to restore native forbs to impoverished sagebrush steppe communities following vast wildfires. This study quantitatively characterized the floral guilds of 17 prevalent wildflower species of the Great Basin that are, or could be, available for restoration seed mixes. More than 3800 bees representing >170 species were sampled from >35,000 plants. Species of Osmia, Andrena, Bombus, Eucera, Halictus, and Lasioglossum bees prevailed. The most thoroughly collected floral guilds, at Balsamorhiza sagittata and Astragalus filipes, comprised 76 and 85 native bee species, respectively. Pollen-specialists dominated guilds at Lomatium dissectum, Penstemon speciosus, and several congenerics. In contrast, the two native wildflowers used most often in sagebrush steppe seeding mixes- Achillea millefolium and Linum lewisii-attracted the fewest bees, most of them unimportant in the other floral guilds. Successfully seeding more of the other wildflowers studied here would greatly improve degraded sagebrush steppe for its diverse native bee communities. [ABSTRACT FROM AUTHOR]

Many specialist herbivores eat foods that are apparently low quality. The compensatory benefits of a poor diet may include protection from natural enemies. Several bee lineages specialize on pollen of the plant family Asteraceae, which is known to be a poor-quality food. Here we tested the hypothesis that specialization on Asteraceae pollen protects bees from parasitism. We compared rates of brood parasitism by Sapyga wasps on Asteraceae-specialist, Fabeae-specialist, and other species of Osmia bees in the field over several years and sites and found that Asteraceae-specialist species were parasitized significantly less frequently than other species. We then tested the effect of Asteraceae pollen on parasites by raising Sapyga larvae on three pollen mixtures: Asteraceae, Fabeae, and generalist (a mix of primarily non-Asteraceae pollens). Survival of parasite larvae was significantly reduced on Asteraceae provisions. Our results suggest that specialization on low-quality pollen may evolve because it helps protect bees from natural enemies. [ABSTRACT FROM AUTHOR]

Background: Many insects have multiple generations per year and cohorts emerging in different seasons may evolve their own phenotypes if they are subjected to different selection regimes. The bivoltine bee Andrena bicolor is reported to be polylectic and oligolectic (on Campanula) in the spring and summer generations, respectively. Neurological constraints are assumed to govern pollen diet in bees. However, evidence comes predominantly from studies with oligolectic bees. We have investigated how sensory constraints influence the innate foraging behavior of A. bicolor and have tested whether bees of different generations evolved behavioral and sensory polyphenism to cope better with the host flowers available in nature when they are active. Results: Behavioral and sensory polyphenisms were tested in choice assays and electroantennographic analyses, respectively. In the bioassays, we found that females of both generations (1) displayed a similar innate relative reliance on visual and olfactory floral cues irrespective of the host plants tested; (2) did not prefer floral cues of Campanula to those of Taraxacum (or vice versa) and (3) did not display an innate preference for yellow and lilac colors. In the electroantennographic analyses, we found that bees of both generations responded to the same set of compounds. Conclusion: Overall, we did not detect seasonal polyphenism in any trait examined. The finding that bees of both generations are not sensory constrained to visit a specific host flower, which is in strict contrast to results from studies with oligolectic bees, suggest that also bees of the second generation have a flexibility in innate foraging behavior and that this is an adaptive trait in A. bicolor. We discuss the significance of our findings in context of the natural history of A. bicolor and in the broader context of host-range evolution in bees. [ABSTRACT FROM AUTHOR]

Celonites fischeri was recorded from ten localities in various open, disturbed habitats in North-West Cyprus. The species is probably narrowly oligolectic exploiting exclusively flowers of Echium (Boraginaceae) as the sole pollen and nectar source. Females perform a pollen collecting strategy hitherto unknown in pollen wasps; they ingest pollen from fresh anthers of Echium flowers that have just started to open by forcing their head into the only slightly opened corolla. Males patrol along Echium plants in search for females. Mating was mainly observed at Echium flowers but also occurred in the area of a male sleeping aggregation. The aerial nest, consisting of 2-5 earthen cells sometimes covered with an additional thin layer of earth, is attached to stones or plants. Nest building and soil collection behaviour are described and an ethogram of a nesting female observed during three consecutive days is given. Males form sleeping aggregations at particular sites that are continuously used over at least eleven consecutive nights, even though the size of the male groups may vary from day to day. During sleeping, the males characteristically curl their bodies around withered stems. [ABSTRACT FROM AUTHOR]

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. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ●●, ●●-●●. [ABSTRACT FROM AUTHOR]

We describe females and males of Osmia (Melanosmia) calaminthae sp. n., an apparent floral specialist on Calamintha ashei (Lamiaceae), and provide observations on the behavior of female bees on flowers of this plant. We also provide diagnostic information for Osmia (Diceratosmia) conjunctoides Robertson, stat. n., and synonymize O. (Diceratosmia) subfasciata miamiensis Mitchell with O. conjunctoides syn. n. Females of both O. calaminthae and O. conjunctoides are unique among North American Osmia for having short, erect, simple facial hairs, which are apparent adaptations for collecting pollen from nototribic flowers. Osmia calaminthae is currently only known from sandy scrub at four nearby sites in the southern Lake Wales Ridge in Highlands County, Florida, USA, while O. conjunctoides is known from limited but widespread sites in the southeastern USA. We discuss the conservation status of both species based on known or speculated floral associates and distributions. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Male bees can be abundant at flowers, particularly floral hosts of those bee species whose females are taxonomic pollen specialists (oligolecty). Contributions of male bees to host pollination are rarely studied directly despite their prevalence in a number of pollination guilds, including those of some crop plants. In this study, males of tbe oligolectic bee, Peponapis pruinosa Say, were shown to be effective pollinators of summer squash. Cucurbita pepo L. Seven sequential visits from male P. pruinosa maximized squash fruit set and growth. This number of male visits accumulated during the first hour of their foraging and mate searching at flowers soon after sunrise. Pollination efficacy of male P. pruinosa and their abundances at squash flowers were sufficient to account for most summer squash production at our study sites, and by extrapolation, to two-thirds of all 87 North American farms and market gardens growing squashes that were surveyed for pollinators by collaborators in the Squash Pollinators of the Americas Survey. We posit that the substantial pollination value of male Peponapis bees is a consequence of their species' oligolecty, their mate seeking strategy, and some extreme traits of Cucurbita flowers (massive rewards, flower size, phenology) [ABSTRACT FROM AUTHOR]

Ptilothrix fructifera is a solitary, oligolectic bee dependent on the flowers of Opuntia (Cactaceae). We conducted field studies to identify the mating tactics used by P. fructifera males and to determine whether factors such as male body size and available resource flowers contribute to variation in male mating tactic. Males in a population in southern Brazil showed pronounced variation in body size, but no distinct size classes. Larger males aggressively defended territories of flowering Opuntia plants, the sole pollen source for the females. Smaller males nonaggressively patrolled nonflowering shrubs growing between the nest aggregation and patches of Opuntia. Only unmated females were attractive to males. When offered to males in patrolled shrubs, up to eight males attempted to mate with the same female, but in territories only the territory owner mated with the introduced female. About 10min after mating, females were unattractive to males. These results identify the species as monogamous and indicate that territoriality is an adaptive mating tactic. Experimental addition of Opuntia flowers to patrolled shrubs showed that nonterritorial males can switch to territorial behaviour. Thus, the number of available flowers together with the number of competitor males determines the ratio of territorial males to patrolling males at a given site. The experiment shows that male P. fructifera show a conditional reproductive strategy in which males adopt alternative tactics according to their size. [Copyright &y& Elsevier]

The article discusses a study on bee genus Meganomia (M.) binghami, comparing its pollen loads and pollen preference with that of M. andersoni and M. gigas. Melittid bees play a role in understanding the evolution and diversification of bees as they represent a branch of bee phylogeny. Study procedure include the performance of a palynological analyses of the pollen from female scopae. Results of such analyses are discussed, relating it to the evolution of host-plant specialization in the Melittidae.

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Andrena hattorfiana is a rare solitary bee which has declined during the last decades throughout western Europe. It is specialised to forage pollen from plants of the family Dipsacaceae. Knowledge of distribution, dispersal propensity, and local population sizes is essential for successful conservation of A. hattorfiana. The investigated local bee populations ( n = 78) were dominated by small local populations and 60% were smaller than 10 female individuals and 80% were smaller than 50 female individuals. The area of the median occupied habitat patch was 1.25 hectare and harboured 7 female bees. Mark-release-recapture studies of female A. hattorfiana revealed a sedentary behaviour. Among pollen-foraging female bees the average registered distance moved was 46 m. The patch emigration rate was about 2%, with an observed maximum colonization distance of 900 m. Only 10% of the individuals crossed areas without the pollen plant within grassland patches, such as unpaved roads, stone walls and small tree-stands, even if these areas were less than 10 m wide. This study shows that solitary bees can occur in local populations of extremely small size and they have a sedentary behaviour. These are features that usually increase the risk of local population extinction. [ABSTRACT FROM AUTHOR]

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. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95, 719–733. [ABSTRACT FROM AUTHOR]

To trace the evolution of host-plant choice in bees of the genus Chelostoma (Megachilidae), we assessed the host plants of 35 Palearctic, North American and Indomalayan species by microscopically analyzing the pollen loads of 634 females and reconstructed their phylogenetic history based on four genes and a morphological dataset, applying both parsimony and Bayesian methods. All species except two were found to be strict pollen specialists at the level of plant family or genus. These oligolectic species together exploit the flowers of eight different plant orders that are distributed among all major angiosperm lineages. Based on ancestral state reconstruction, we found that oligolecty is the ancestral state in Chelostoma and that the two pollen generalists evolved from oligolectic ancestors. The distinct pattern of host broadening in these two polylectic species, the highly conserved floral specializations within the different clades, the exploitation of unrelated hosts with a striking floral similarity as well as a recent report on larval performance on nonhost pollen in two Chelostoma species clearly suggest that floral host choice is physiologically or neurologically constrained in bees of the genus Chelostoma. Based on this finding, we propose a new hypothesis on the evolution of host range in bees. [ABSTRACT FROM AUTHOR]

1. Reliable methods for quantifying population size are crucial for strategies to conserve endangered wild-bee species. Estimates of population size obtained through survey walks were compared with estimates obtained through mark–recapture studies in 10 populations of the red-listed solitary bee Andrena hattorfiana in southern Sweden. 2. The mean number of bees observed during survey walks was strongly correlated with estimates of population size obtained with mark–recapture. It was found that 5.5–23.4% (mean 13.4%) of the total population was observed during an average survey walk. 3. One component in mark–recapture analysis is the measure of survival of individuals. In the largest bee population, females of A. hattorfiana that emerged in early season were found to forage for pollen on average 18.4 days. 4. The findings suggest that during large-scale surveys, for example re-inventories for red-listed species, the population size of solitary bees can be quantified reliably and effectively by performing survey walks in a two-step process. The first step consists of survey walks to establish the relationship between number of bee observations per survey walk and mark–recapture population size for a small set of populations. In the second, simple observation survey walks can be performed for a large set of populations. In each population of A. hattorfiana, it is recommended that at least six survey walks are performed. [ABSTRACT FROM AUTHOR]

Rewardless kettle-trap flowers Cypripedium yunnanense and C. flavum were watched for pollinators during 73 and 101 man-hours, respectively, in north-west Yunnan at 3490–3590 m a.s.l. They differ from typical Cypripedium, such as C. calceolus, in having a broad infolded flap of the lip extending all around the entrance of the pouch (instead of being restricted to the vicinity of the staminode) and in the flap not being slippery. Cypripedium yunnanense is pollinated by Lasioglossum zonulum euronotum (Halictidae), and C. flavum is pollinated by Andrena orchidea and Andrena sp. (Andrenidae, two of nine new hymenopterans discovered at the sites). The bees do not inadvertently fall into the trap by slipping (as often occurs in other slipper orchids), but enter it by crawling down the flap in full control of their movements. No natural hybrids between the two orchids are known, although they occur in close-by or mixed stands, are co-flowering and size compatible with regard to their pollinators, and produce fruits following manual cross-pollination in situ. Analyses of the (non- Cypripedium) pollen carried indicate that: (1) the two andrenids are probably oligolectic; (2) the andrenids and the halictid do not share the same flower species; and (3) the halictid is polylectic. Points (1) and (2) are probable reasons for the lack of hybrids. The other reason why Lasioglossum zonulum euronotum does not visit C. flavum despite being polylectic may be the flower's odour; cases of discrimination of closely related flowers by polylectic Lasioglossum have been reported elsewhere. Blow flies Calliphora vomitoria and Calliphora pattoni (Calliphoridae) also enter the orchids, some smearing themselves with pollen, yet they are not pollinators. They are too large to leave by the exit and die imprisoned. However, they may be accidental pollinators of the rather larger C. tibeticum present at the sites. Such accidental pollinators probably play an important role in the evolution of new pollination syndromes. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 156, 51–64. [ABSTRACT FROM AUTHOR]

We investigated several aspects of the nesting biology of Epicharis metatarsalis Friese (Hymenoptera: Apidae) in a lowland wet-forest of northeastern Costa Rica. Five large aggregations were found 30-100 m from larger rivers at the La Selva Biological Station. The relatively short nesting season, from May to August, indicates that E. metatarsalis is probably univoltine. Four nests were excavated to study nest architecture, and five brood cells from three different nests were analyzed for pollen composition. Additionally, we analyzed pollen loads from 33 females returning from pollen-collecting trips, and we observed male patrolling behavior. The canopy tree Apeiba membranacea Spruce ex Benth (Tiliaceae) was found to be the principal pollen source, representing an average proportion of 98.5% of each pollen load and 93.4% of the larval provisions. The brood cell with the lowest proportion of A. membranacea pollen contained 89.3% A. membranacea pollen, which was 98.5% by relative volume. Pollen of Byrsonima crispa A. Juss. (Malpighiaceae) was the second most frequently encountered pollen with average proportions of 1.3 and 4.9% in pollen loads and larval provisions, respectively. E. metatarsalis can thus be considered oligolectic. The E. metatarsalis nesting season coincides with the relatively short flowering season of B. crispa, perhaps because of the importance of B. crispa as a source of oils rather than nectar. [ABSTRACT FROM AUTHOR]

Abstract: The native bee fauna provides an important ecosystem function, but a large proportion of this fauna in Europe is threatened as a result of habitat loss and fragmentation. The solitary bee Andrena hattorfiana is specialised on collecting pollen from the plant-family Dipsacaceae. In northern Europe the major pollen resource is the insect-pollinated herb Knautia arvensis. We quantified the available K. arvensis resource, measured habitat characteristics and performed a flower-visitor survey in 57 well-defined K. arvensis populations in southern Sweden. There was a strong relationship between bee and plant population sizes. In populations with A. hattorfiana present (N =26), the female bees utilised on average 39% (12–80%) of the total available pollen resource. The nest architecture and nesting biology of A. hattorfiana is described for the first time. By excavating nests, we found that the provisioning for one average bee nest (containing 6 cells) required ca. 72 inflorescences or 11 plant individuals. The results suggest a certain minimum pollen amount needed to host an A. hattorfiana population. For example, for a population of ten reproducing A. hattorfiana ♀ with the average degree of utilisation, the critical resource was predicted as 156±16 individuals (±SE) of the plant K. arvensis, which corresponds to 780 inflorescences or 36,731,978 pollen grains. These findings suggest that calculations via a ‘pollen budget’ can predict critical resources for a given size of specialised bee population, and thereby provide a tool in conservation. [Copyright &y& Elsevier]

The article discusses the study on the complex responses within a desert bee guild to urban habitat fragmentation. The authors compared species incidence and abundance patterns for the bee guild visiting at 59 habitat fragments of known size and age and in adjacent desert. The comparison was done in order to evaluate the response of bee fauna to fragmentation. The 62 bee species used in the study responded to fragmentation and not in direct relation to their abundance or incidence in undisturbed desert. Overall, bee response to urban habitat fragmentation was best practiced by ecological traits associated with nesting and dietary breadth.