Why do leafcutter bees cut leaves? New insights into the early evolution of bees

Stark contrasts in clade species diversity are reported across the tree of life and are especially conspicuous when observed in closely related lineages. The explanation for such disparity has often been attributed to the evolution of key innovations that facilitate colonization of new ecological niches. The factors underlying diversification in bees remain poorly explored. Bees are thought to have originated from apoid wasps during the Mid-Cretaceous, a period that coincides with the appearance of angiosperm eudicot pollen grains in the fossil record. The reliance of bees on angiosperm pollen and their fundamental role as angiosperm pollinators have contributed to the idea that both groups may have undergone simultaneous radiations. We demonstrate that one key innovation--the inclusion of foreign material in nest construction--underlies both a massive range expansion and a significant increase in the rate of diversification within the second largest bee family, Megachilidae. Basal clades within the family are restricted to deserts and exhibit plesiomorphic features rarely observed among modern bees, but prevalent among apoid wasps. Our results suggest that early bees inherited a suite of behavioural traits that acted as powerful evolutionary constraints. While the transition to pollen as a larval food source opened an enormous ecological niche for the early bees, the exploitation of this niche and the subsequent diversification of bees only became possible after bees had evolved adaptations to overcome these constraints.     

Monitoring bee populations: are eusocial bees attracted to different colours of pan trap than other bees?

Declines in pollinator populations have made monitoring pollinators, in particular bees, increasingly important. There is general agreement among practitioners that using a mix of trap colours is important, but the empirical evidence to support this is scattered. During studies of bees in forestry cutovers, large differences were noted in capture rate among white, blue, and yellow pan traps. Pooled data from collections in cutovers and commercial cranberry fields demonstrated significant differences in the effect of trap colour, with the largest numbers captured in white traps, and the fewest in yellow, but only for the genus Bombus Latreille (Hymenoptera: Apidae). The colour preference was consistent with the spectral sensitivity of Bombus, and the visible reflectance spectra of the traps. A literature review suggested that among eusocial bees, Apis Linnaeus (Hymenoptera: Apidae) are more attracted to white traps and Bombus are more attracted to blue traps, while non-eusocial bees with a variety of social structures are more attracted to yellow. Among the non-eusocial bees, Halictidae were somewhat attracted to blue, while Andrenidae were not. This supports the common practice of using white, blue, and yellow traps when surveying bees to ensure adequate taxonomic representation.     

Why do bees turn back and look?

The timing of learning of colour and shape of the food source, as well as of near-by landmarks, was examined exploiting a behaviour described recently, the Turn Back and Look behaviour (TBL): Bees departing from a novel food source after feeding turn around to view it at a short distance (Figs. 2, 3) before departing for the hive. They repeat this behaviour on several successive visits, termed the TBL phase (Fig. 5). To examine the function of the TBL, I trained individual bees in 4 different modes. In the first 3 they could view a food source or a landmark of a particular colour or shape during (i) arrival as well as departure, (ii) only arrival, and (iii) only departure; in the final mode (iv) the bees viewed one colour (or shape) on arrival, and another on departure. At the end of the TBL phase, the bees were tested by offering them a choice between the visual stimulus to which they were trained (modes i–iii) and a different (novel) one, or between the stimulus viewed on arrival and that viewed on departure (mode iv). The test results show that learning after feeding (while performing the TBL), i.e. backward conditioning, occurs regardless of whether the colour (Fig. 6, Fig. 10a) or shape (Fig. 7) of the food source, or the colour (Fig. 10b), shape (Fig. 11), and position (Fig. 12) of a near-by landmark is considered. Bees trained in mode (iv) preferred the stimulus learned on arrival over that learned on departure in almost all cases. However, a stimulus viewed exclusively on departure (mode iii) was often learned as well as when it was viewed exclusively on arrival (mode ii) (Figs. 10a, 11, 12), or both on arrival and departure (mode i) (Fig. 6). The finding that the timing of learning can be manipulated suggests that it is not based on hard wired predispositions to learn particular visual cues on arrival, and others on departure.     

Social behavior and nests of some nomiine bees in India (Hymenoptera,Halictidæ)

Summary Social or semisocial behavior in nomiine bees is here reported for the first time. InNomia capitata and perhaps inN. oxybeloides, presumed sister bees share cell clusters and cooperatively provision the same cells. Unlike other primitively social bees, the sisters simultaneously forage and oviposit. There is no apparent inhibition of the oviposition of daughters, although their nest-founding mother or perhaps an older sister appears to stay in the nest and continue to oviposit.Nesting behavior and nest structure ofNomia capitata andN. oxybeloides are similar; cells are vertical and clustered. In contrastNomia nasicana makes horizontal cells scattered along the main burrow.

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Zusammenfassung Zum ersten Mal wird über soziales oder halbsoziales Verhalten von Bienen aus der Unterfamilie der Nomiinen berichtet. BeiNomia capitata und vielleicht auch beiN. oxybeloides teilen sich mehrere Bienen—wahrscheinlich Schwestern—ein und denselben Zellkomplex und verproviantieren auch die Zellen gemeinsam. Ganz im Gegensatz zu anderen sozial primitiven Bienen verproviantieren diese Nestgenossen nicht nur, sondern legen auch Eier. Die Fähigkeit Eier zu produzieren ist in diesen Bienen offenbar nicht unterdrückt, obwohl sich in jedem Nest ein eierlegendes Individuum befindet, die entweder die Nestgründerin, oder eine ältere Schwester sein muss. Im Nistverhalten und in der Struktur der Nester sind sichN. capitata undN. oxybeloides sehr ähnlich. Die Zellen stehen vertikal und sind in Gruppen angeordnet. Im Gegensatz dazu fertigtN. nasicana horizontal liegende Zellen, die entlang eines Tunnels verteilt sind.

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Résumé Un comportement social est décrit pour la première fois chez des abeilles nomiine. ChezNomia capitata et probablementN. oxybeloides, il existe des abeilles surs qui partagent les cellules et les approvisionnent ensemble. Contrairement à d'autres abeilles à comportement social primitif, les surs butinent et pondent des ufs simultanément. Les filles ne montrent pas d'inhibition apparente de ponte malgré que leur mère ayant bâtit le nid, ou peut-être une vieille sur, reste dans le nid et continue à pondre des ufs.Le comportement et la structure des nids desNomia capitata, N. oxybeloides etNomia nasicana sont décrits.

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Contribution No 1304 from the Department of Entomology, The University of Kansas, Lawrence. This paper is the second of a series on behavior of Halictidae in India; the others areBatra andMichener (1966) andBatra (1966).     

How do bees learn and recognize visual patterns?

The basic task of perceptual systems is the recognition and localization of objects. The central nervous system has to solve these problems on the basis of the excitation patterns of sensory nerves, in spite of the fact that these provide only ambiguous information about objects. Two processing principles seem to be fundamental for an efficient formation of object representations: the extraction of characteristic features and the ability to assess similarities between different objects. This article reviews investigations in which different training paradigms were applied in order to explore the honeybee's capacities to learn and recognize visual patterns. One aim of these experiments is to assess whether insects use similar processing mechanisms as vertebrates, for instance human beings. By comparing the computational performance of perceptual systems in animals with different evolutionary history we can hope to learn more about the operation of basic rules in nervous systems. “The messages which the brain receives have not the least similarity with the stimuli. They consist in pulses of given intensities and frequencies, characteristic for the transmitting nerve-fiber, which ends at a definite place of the cortex. ... From this information it produces the image of the world by a process which can metaphorically be called a consummate piece of combinatorial mathematics: it sorts out of the maze of indifferent and varying signals, invariant shapes and relations which form the world of ordinary experience.” Max Born (1949) Received: 4 October 1997 / Accepted in revised form: 26 August 1998     

The birds, the bees, and the virtual flowers: can pollinator behavior drive ecological speciation in flowering plants?

Biologists have long assumed that pollinator behavior is an important force in angiosperm speciation, yet there is surprisingly little direct evidence that floral preferences in pollinators can drive floral divergence and the evolution of reproductive (ethological) isolation between incipient plant species. In this study, we expose computer-generated plant populations with a wide variation in flower color to selection by live and virtual hummingbirds and bumblebees and track evolutionary changes in flower color over multiple generations. Flower color, which was derived from the known genetic architecture and phenotypic variance of naturally occurring plant species pollinated by both groups, evolved in simulations through a genetic algorithm in which pollinator preference determined changes in flower color between generations. The observed preferences of live hummingbirds and bumblebees were strong enough to cause adaptive divergence in flower color between plant populations but did not lead to ethological isolation. However, stronger preferences assigned to virtual pollinators in sympatric and allopatric scenarios rapidly produced ethological isolation. Pollinators can thus drive ecological speciation in flowering plants, but more rigorous and comprehensive behavioral studies are required to specify conditions that produce sufficient preference levels in pollinators.     

Bacillus DNA in fossil bees: an ancient symbiosis?

We report here the isolation of DNA from abdominal tissue of four extinct stingless bees (Proplebeia dominicana) in Dominican amber, PCR amplification of a 546-bp fragment of the 16S rRNA gene from Bacillus spp., and their corresponding nucleotide sequences. These sequences were used in basic local alignment search tool searches of nonredundant nucleic acid data bases, and the highest scores were obtained with 16S rRNA sequences from Bacillus spp. Phylogenetic inference analysis by the maximum-likelihood method revealed close phylogenetic relationships of the four presumed ancient Bacillus sequences with Bacillus pumilus, B. firmus, B. subtilis, and B. circulans. These four extant Bacillus spp. are commonly isolated from abdominal tissue of stingless bees. The close phylogenetic association of the extracted DNA sequences with these bee colonizers suggests that a similar bee-Bacillus association existed in the extinct species P. dominicana.     

Euglossine bees as potential bio-indicators of coffee farms: does forest access, on a seasonal basis, affect abundance?

In order to understand the implications of agriculture on the environment, ecosystem health must be measured. Observing the presence of a biological indicator within an ecosystem is one such method. In this study, male euglossine bees were observed using as attractant cineole 1:8, at adjacent organic (La Paz) and conventional (La Carena) coffee farms near the Northern Barranca River, San Ramón, Alajuela, Costa Rica. Simultaneous data collections were conducted on both farms in April 2004 (late-dry season) and June 2004 (early-rainy season) and combined with the findings of August 2004 (mid-rainy season). These observations show that orchid bees are a viable bio-indicator of organic farm health on a seasonal basis. In the dry season there was no significant difference in orchid bee abundance between the two farms. There is a strong tendency for more bees during the rainy season, suggesting that orchid bee abundance is linked to seasonality and forest access.     

Pollen harvest by solitary bees (Ptilothrix relata,Hym. Apidae,Emphorini) in the Argentine pampas – preliminary results

In order to determine the plants foraged by solitary Ptilothrix relata, the pollen content of food provisions was identified. The main pollen types confirm foraging by these bees on Malvaceae, Asteraceae and Onagraceae. Pollen sources belonging to Cucurbitaceae, Dipsacaceae and Portulacaceae families enrich the harvesting range of P. relata. According to the preliminary results, these bees can be considered more as narrowly polylectic than oligolectic because they collect pollen from a few unrelated species. Among the most abundant pollen collected, two major morphological types were recognized: (1) pollen with long spines (4–25?μm), many single apertures and large size (115–135?μm of diameter); and (2) tricolporate pollen with viscin threads.     

Diversity of bees and their floral resources at altitudinal areas in the Southern Espinhaço Range, Minas Gerais, Brazil

The Southern Espinha?o Range consists of large areas covered by quartzitic or metaliferous tropical altitudinal fields. The Espinha?o Range ecosystems are endangered by anthropic high impacts, particularly due to mining and urbanization. We conducted a one-year inventory of the bee flora and fauna at the quartzitic Ouro Branco Mountains and a two-year survey of the metaliferous Ouro Preto fields. The samples were collected twice a month, from 8:00 am to 5:00 pm. The bees (677) belonged to 91 species, five families. The family Apidae was the richest and most abundant, followed by the Halictidae and Megachilidae. The bees visited 46 flowering plant species; the most visited plants were the Asteraceae (n = 220), the Malpighiaceae (n = 95), the Melastomataceae (n = 94), the Fabaceae (n = 78), and the Solanaceae (n = 63). Diversity was higher in Ouro Branco (H = 1.47) than in Ouro Preto (H = 1.17). The low richness and abundance of bees in our research site when compared to other Brazilian "Cerrado" areas can be due to the high altitude, low temperature, and low availability of flowers we found. "Canga" and rupestrian areas house fauna and flora species that are rare and threatened by extinction. The southern Espinha?o areas can, therefore, be given the status of permanent biodiversity preservation area.     

Why do nectar-foraging bees and wasps work upwards on inflorescences?

Summary Wasps (Dolichovespula and Vespula spp.) worked predominantly upwards when foraging for nectar on inflorescences of the protogynous Scrophularia aquatica, in which the standing crop of nectar sugar per flower showed no clear pattern of vertical distribution up an inflorescence. Bumblebees taking nectar (Bombus hortorum visiting legally, and certain individuals of B. terrestris which positioned themselves head-upwards while taking nectar through holes bitten in the corolla) worked predominantly upwards on the racemose inflorescences of Linaria vulgaris, although the standing crop of nectar sugar per open flower increased up the raceme. Individuals of B. terrestris which robbed Linaria flowers in a head-down position worked predominantly downwards on inflorescences. The upward or downward directionality of intra-inflorescence movements by foraging insects may depend in part on the position these adopt during their flower visits.     

Environment or kin: whence do bees obtain acidophilic bacteria?

As honey bee populations decline, interest in pathogenic and mutualistic relationships between bees and microorganisms has increased. Honey bees and bumble bees appear to have a simple intestinal bacterial fauna that includes acidophilic bacteria. Here, we explore the hypothesis that sweat bees can acquire acidophilic bacteria from the environment. To quantify bacterial communities associated with two species of North American and one species of Neotropical sweat bees, we conducted 16S rDNA amplicon 454 pyrosequencing of bacteria associated with the bees, their brood cells and their nests. Lactobacillus spp. were the most abundant bacteria in many, but not all, of the samples. To determine whether bee-associated lactobacilli can also be found in the environment, we reconstructed the phylogenetic relationships of the genus Lactobacillus. Previously described groups that associate with Bombus and Apis appeared relatively specific to these genera. Close relatives of several bacteria that have been isolated from flowers, however, were isolated from bees. Additionally, all three sweat bee species associated with lactobacilli related to flower-associated lactobacilli. These data suggest that there may be at least two different means by which bees acquire putative probiotics. Some lactobacilli appear specific to corbiculate apids, possibly because they are largely maternally inherited (vertically transmitted). Other lactobacilli, however, may be regularly acquired from environmental sources such as flowers. Sweat bee-associated lactobacilli were found to be abundant in the pollen and frass inside the nests of halictids, suggesting that they could play a role in suppressing the growth of moulds and other spoilage organisms.     

Floral constancy in bumble bees: handling efficiency or perceptual conditioning?

Individual bees often prefer flowers of the same species that they are already foraging on, and other individual bees prefer other flowers. This floral constancy has classically been explained as a learned behavior by which bees avoid wasting time switching between handling techniques. Choice trails were given to Bombus vagans workers that were freely foraging in mixed and pure fields of Trifolium pratense, T. repens, Viccia cracca, and Prunella vulgaris. Contrary to expectation, (1) bees showed if anything a stronger preference for their flower type in pure fields where they lacked experience than in a mixed field where they had had the opportunity to learn, (2) there was greater constancy in a mixed field of the two morphologically similar Trifolium species than in a mixed field of the morphologically disparate T. pratense and P. vulgaris, and (3) bees were more willing to switch between flowers of distinct morphologies when the colors were similar than between flowers of distinct colors when the morphologies were similar. We suggest that constancy is due to some form of perceptual conditioning whereby individual bees become temporarily sensitized to one or a few floral cues.     

Spider signals: are web decorations visible to birds and bees?

We are becoming increasingly aware of animal communication outside the range of human sensitivity. Web decorations are silk structures used by orb-web spiders to deceive prey and predators. However, despite the level of interest in these structures, their visibility to prey and predators has never, to our knowledge, been objectively assessed. Here, we use spectrophotometric analyses to show that the decorations of all five tested spider species are visible to honey bees and birds over short and long distances. Furthermore, the discoid decorations of one species may provide some protection against arthropod predators. However, these decorations are inefficient at camouflaging the spider against birds, despite the overlap between the spider's body and web decoration.     

Are body size and volatile blends honest signals in orchid bees?

Secondary sexual traits may convey reliable information about males’ ability to resist pathogens and that females may prefer those traits because their genes for resistance would be passed on to their offspring. In many insect species, large males have high mating success and can canalize more resources to the immune function than smaller males. In other species, males use pheromones to identify and attract conspecific mates, and thus, they might function as an honest indicator of a male's condition. The males of orchid bees do not produce pheromones. They collect and store flower volatiles, which are mixed with the volatile blends from other sources, like fungi, sap and resins. These blends are displayed as perfumes during the courtship. In this study, we explored the relationship between inter‐individual variation in body size and blend composition with the males’ phenoloxidase (PO) content in Euglossa imperialis. PO content is a common measure of insect immune response because melanine, its derived molecule, encapsulates parasites and pathogens. Body size and blend composition were related to bees’ phenolic PO content. The inter‐individual variation in body size and tibial contents could indicate differences among males in their skills to gain access to some compounds. The females may evaluate their potential mates through these compounds because some of them are reliable indicators of the males’ capacity to resist infections and parasites.     

Why are there so many species of bumble bees at Dungeness?

WILLIAMS, P. H., 1989. Why are there so many species of bumble bees at Dungeness? Dungeness is unique in the British Isles in that it has more species of bumble bees than any other locality. Three ideas about what governs the number of species at a locality are examined by locking at patterns of flower visits at Dungeness in comparison with those at Shoreham, a species-poor locality also in Kent. The species of bumble bees that are present at Dungeness but absent from Shoreham show no association in their distributions among 2 km grid-squares in Kent with the species of food-plants that they prefer at Dungeness, nor is there any correlation between the diversity of bees and diversity of food-plants at Dungeness and Shoreham. From the information available, Dungeness is most likely to have more species of bumble bees because it has a particularly high density of the more nectar-rich flowers that bumble bees can use. Bumble bees feed most profitably from deep flowers because these contain more nectar than shallow flowers, although direct access to deeper flowers is ultimately limited by the length of each bee's proboscis. The distribution of worker proboscis lengths among species in the species-pool in Kent is clumped about a median of 7.9 mm. The best foraging conditions for the maximum number of species should be provided when flowers of similar depths are present in sufficiently large numbers for all foragers to make near-optimal flower choices. Although there is no difference in median between the distributions of the bees' proboscis lengths and the depths of the flowers they use at Dungeness, at Shoreham the flower depths used are shorter than the proboscis lengths. Among the food-plants at Dungeness, high densities of Teucrium scorodonia and Echium vulgare are likely to be especially important.