THE ROLE OF RESIN IN ANGIOSPERM POLLINATION: ECOLOGICAL AND CHEMICAL CONSIDERATIONS

Members of at least two unrelated genera of plants, Dalechampia (Euphorbiaceae) and Clusia (Guttiferae), attract pollinators by secreting resins from floral structures. Bees that pollinate these flowers collect and use the resin in nest construction; these include Euglossa, Eulaema, Eufriesea, Trígona and, Hypanthidium in the neotropics, and Heriades in Africa. Floral resins are slow in hardening as compared with many other plant resins; this facilitates collection and storage by bees, hence probably enhancing the attractiveness of the flowers. Floral resins are probably of great utility and dependability and may be an especially important resource to certain bees, which in turn are major pollinators of many species of tropical plants. Bees appear to forage floral resin using a “strategy” of energy efficiency; large bees collect resin only from copious sources, smaller bees collect resin from sources with small amounts as well as from sources with large amounts of resin. Resin secretion in flowers may have originated as defense against herbivores and secondarily assumed the role of pollinator reward.     

Nesting aggregation as a predictor of brood parasitism in mason bees (Osmia spp.)

1. Parasitism can be an important source of mortality for insect populations; however, we know little about the factors influencing vulnerability of wild bees to parasites. Mason bees (genus Osmia; Hymenoptera: Megachilidae) are important pollinators of crops and wild plants and are vulnerable to attack by brood parasites. High nest densities may increase rates of brood parasitism by attracting disproportionate numbers of parasites. 2. Three years of field observations from multiple sites were analysed to assess whether mason bee brood parasitism increased with host density. Mason bees were allowed to nest in artificial nesting blocks and establish natural variation in nesting density. Nest cells constructed by bees were checked for the presence of parasite eggs. 3. Parasitism of nest cells strongly increased with the number of actively nesting bees at a nesting block. Mason bees showed no preference for nesting in blocks that were occupied or unoccupied by other mason bees. Parasitism also increased with the number of days a nest was provisioned and decreased over the course of the season. Nest cells constructed last in a nest were significantly more parasitised than inner cells, despite being sealed against invasions. 4. These findings show positively density‐dependent parasitism in mason bees. They also suggest that bees terminate parasitised nests, causing parasitised cells to become outermost nest cells – a behaviour that may represent a defence against parasites. Our results have implications for the management of mason bees as agricultural pollinators, as cultivating them at high densities could reduce offspring survival.     

Social parasites among African allodapine bees (Hymenoptera,Anthophoridae, Ceratinini)*

Among the numerous nonparasitic allodapine bees there are 11 known species with parasitic or probably parasitic habits. These species live in nests of their close relatives, the female parasite replacing an egg-layer of the host. Seven of the parasitic species are distributed among four otherwise nonparasitic genera, while four species of parasites are placed in three exclusively parasitic genera. The parasites have mostly arisen independently from different nonparasitic forms. There is much convergence among the parasitic forms involving such characters as the flattened or concave face, reduced eyes, reduced mouthparts, reduced wing venation, and reduced pollen-carrying scopa. In the most specialized parasitic genera the mouthparts are so small as to be almost surely useless for obtaining food from flowers. Such bees must feed in the host nest, and are not found on flowers. Their wings must be adequate to take them to a new host nest but the reduced venation and eyes must reflect the reduced locomotary and sensory needs of a bee that does not visit flowers. In this paper a new, presumably parasitic Allodapula is described as is a parasitic Braunsapis, a parasitic Allodape, and a Eucondylops. A previously described Macrogalea is recognized as a parasite for the first time. A new genus and species of parasites Nasutapsis straussorum, allied to Braunsapis, is also described. All these forms are from Africa.     

Landmark orientation during the approach to the nest in the stingless beeTrigona (Tetragonisca) angustula (Apidae,Meliponinae)

Summary We displaced a small nest box containing stingless bees (Trigona (Tetragonisca)angustula) over distances of up to 1.6 meters in different directions and counted the numbers of returning foragers to measure the effects of this manipulation on the homing ability of bees. Bees find it hard to locate the nest box when it was displaced more than about 1 m backwards, forwards or sideways relative to the direction into which the nest entrance pointed. They do not find the nest when its height above ground is changed. The bees use landmarks in the vicinity of the nest to locate it: When the nest box is displaced and landmark positions are changed so that their angular position at the new nest site is the same as at the normal nest position their homing ability is less impaired than it is without changes in landmark positions. Our results show that the bees do not use the nest box itself as a landmark until they have approached the nest position to within about 1 meter with the aid of surrounding landmarks.     

Flower choice copying in bumblebees

We tested a hypothesis originating with Darwin that bees outside the nest exhibit social learning in flower choices. Naive bumblebees, Bombus impatiens, were allowed to observe trained bees or artificial bees forage from orange or green flowers. Subsequently, observers of bees on green flowers landed more often on green flowers than non-observing controls or observers of models on orange flowers. These results demonstrate that bumblebees can change flower choice by observations of non-nest mates, a novel form of social learning in insects that could provide unique benefits to the colony.     

Adaptive behaviour of honeybees (Apis mellifera) toward beetle invaders exhibiting various levels of colony integration

Social bees generally host fewer nest invaders than do ants and termites. This is potentially explained by the adaptive defensive strategies of host bees when faced with nest invaders exhibiting various levels of colony integration (based on adaptations to the nest habitat and frequency of nest inhabitation). In the present study, experiments are performed to determine the behaviour at the nest entrance of European honeybee guards Apis mellifera L. (Hymenoptera: Apidae) toward beetle invaders of various levels of behavioural integration into colonies. The species used to test this include Aethina tumida Murray (Coleoptera: Nitidulidae), which is regarded as a highly integrated, unwelcome guest (synechthran) or true guest (symphile); Lobiopa insularis Laporte (Coleoptera: Nitidulidae) and Epuraea luteola Erichson (Coleoptera: Nitidulidae) that are accidentals; and Carpophilus humeralis Fabricius (Coleoptera: Nitidulidae), Carpophilus hemipterus L. (Coleoptera: Nitidulidae) and Tribolium castaneum Herbst (Coleoptera: Tenebrionidae), all of which are species that are not integrated into honeybee colonies. The responses of guard bees to a control bead also are noted. In general, bees ignore T. castaneum and E. luteola to a greater extent than other beetle species. Bees make contact with the black glass bead (a non‐aggressive behaviour) more than they do all beetle species. Bees treat A. tumida more defensively than they treat any other beetle species and the level of bee defensiveness varies by colony. These data suggest an adaptive heightened defensive response by bees toward the most integrated colony intruder but a significantly reduced level of response toward invaders representing all other levels of colony integration.     

Deceptive orchids with Meliponini as pollinators

Visitation of orchids by Meliponini (stingless bees) is confirmed only in 13Melipona, Partamona andTrigona, forXylobium andMaxillaria, with the addition ofTrigona fulviventris visitingIonopsis. Some bees evinced multiple floral visitation by carrying several stipes and viscidia from pollinaria, thus may cause seed set. None foraged pseudopollen, nor is collection of this substance by bees verified. Meliponine-visited orchids had pollinia in quartets with emplacement on the bee's scutellum, possibly devices for pollinia survival on a social bee passing through its nest. Further, orchids produced no nectar, but bees repeatedly came to flowers. A testable basis for the orchid-meliponine relationship is mimicry of rewarding resources, or bee pheromone mimicry, recently documented for some honey bees. Meliponine pheromone analogs (nerol and 2-heptanol) are here noted forMaxillaria, but lack of foraging with pheromones byMelipona suggests multiple avenues of mimicry by orchids, including alarm pheromone and carrion mimicry.     

Nest boxes for Cape Parrots Poicephalus robustus in the Hogsback area,Eastern Cape,South Africa

Breeding propensity of tree-cavity nesting bird species are often limited by a shortage of natural nesting sites. Artificial nests can be used to provide alternative nest sites. Cape Parrots Poicephalus robustus are nationally endangered and nest in existing tree-cavities in high-altitude fragmented Afromontane forests in South Africa, assumed to be in short supply due to historic and current logging practices. To increase nest site availability, 179 wooden bird boxes and 28 bee boxes (to ‘pull’ bees) were erected during 2011–2012 in Hogsback, Eastern Cape. In 2016, no bird boxes were occupied by Cape Parrots. A total of 43% were used by other species, 51% were unused and 6% could not be inspected due to tree instability and inaccessibility. Two bird boxes were inspected by two pairs of Cape Parrots, but were never occupied. Occupancy of boxes by birds was not associated with nest, tree or habitat characteristics. However, occupancy of boxes by bees was associated with habitat type and tree species. Future conservation efforts will include locating natural Cape Parrot nesting sites and reforestation efforts to ensure the long-term availability of natural nesting sites.     

Effectiveness of short‐tongued bees as pollinators of apparently ornithophilous New Zealand mistletoes

Abstract The flowers of two species of threatened New Zealand mistletoes (Peraxilla tetrapetala and Peraxilla colensoi, Loranthaceae) have explosive buds that do not open unless force is applied by birds or two species of native short‐tongued bees. Opened flowers are visited by a variety of birds and insects. Although both species of Peraxilla conform to a pollination syndrome of ornithophily, bees may be effective alternative pollinators. We investigated the effectiveness of bees and birds as pollinators of P. colensoi at one site and P. tetrapetala at two sites in the South Island. Bees and other insects outnumbered birds as flower visitors at all three sites. By excluding birds with wire cages, we showed that two bee species regularly open flowers of P. tetrapetala, but only rarely open flowers of P. colensoi. Few pollen grains were deposited when either birds or bees opened buds, so opening buds was not by itself sufficient for adequate pollination. Instead, pollen continued to accumulate over the next 6 or 7 days, even inside cages that excluded birds. Both populations of P. tetrapetala were regularly pollen‐limited, but in different ways. At Ohau, opened flowers gained enough pollen to produce seeds, but many buds were not opened and hence failed to set seed. In contrast, at Craigieburn, nearly all buds were opened, but many of these did not receive enough pollen. These results demonstrate that native bees can partially replace birds as pollinators of mistletoes, despite their apparent ornithophilous syndrome. Ongoing reductions in New Zealand forest bird numbers means that the service bees provide may be important for the long‐term future of these plants.     

Orchard pollination in Capitol Reef National Park,Utah, USA. Honey bees or native bees?

Capitol Reef National Park in central Utah, USA surrounds 22 managed fruit orchards started over a century ago by Mormon pioneers. Honey bees are imported for pollination, although the area in which the Park is embedded has over 700 species of native bees, many of which are potential orchard pollinators. We studied the visitation of native bees to apple, pear, apricot, and sweet cherry over 2 years. Thirty species of bees visited the flowers but, except for pear flowers, most were uncommon compared to honey bees. Evidence that honey bees prevented native bees from foraging on orchard crop flowers was equivocal: generally, honey bee and native bee visitation rates to the flowers were not negatively correlated, nor were native bee visitation rates positively correlated with distance of orchards from honey bee hives. Conversely, competition was tentatively suggested by much larger numbers of honey bees than natives on the flowers of apples, apricots and cherry; and by the large increase of native bees on pears, where honey bee numbers were low. At least one-third of the native bee species visiting the flowers are potential pollinators, including cavity-nesting species such as Osmia lignaria propinqua, currently managed for small orchard pollination in the US, plus several fossorial species, including one rosaceous flower specialist (Andrena milwaukiensis). We suggest that gradual withdrawal of honey bees from the Park would help conserve native bee populations without decreasing orchard crop productivity, and would serve as a demonstration of the commercial value of native pollinators.     

Vibration Signal Modulates the Behavior of House-hunting Honey Bees (Apis mellifera)

Honey bees ( Apis mellifera ) in house-hunting swarms perform vibration signals (dorsoventral abdominal vibration (DVAV)) of 18.05 ± 0.45 Hz for 1.36 ± 0.23 s throughout the house selection process. These signals are performed by a specialized subset of bees, most of whom never perform recruitment dances to nest sites. Individuals repeatedly vibrate others. The patterns of vibration signal performance are consistent with the hypothesis that it serves to activate bees for take-off, but may also activate bees to scout for nest sites.     

Distinguishing signals and cues: bumblebees use general footprints to generate adaptive behaviour at flowers and nest

Chemicals used in communication are divided into signals and cues. Signals are moulded by natural selection to carry specific meanings in specific contexts. Cues, on the other hand, have not been moulded by natural selection to carry specific information for intended receivers. Distinguishing between these two modes of information transfer is difficult when animals do not perform obvious secretion behaviours. Although a number of insects have been suspected of leaving cues at food sites and nest entrances, studies have not attempted to experimentally distinguish between cues and signals. Here, we examine the chemical composition of the scent marks left by the bumblebee Bombus terrestris at food sites and compare it to those found at a neutral location. If bees are depositing a cue, we expect the same chemicals to be found at both sites, but if they deposit a signal we only expect to find the scent marks at the food site. We were also interested in identifying the chemicals left at the nest entrance to determine if they differed from those used to mark food sites. We find that bees deposit the same chemicals at food, nest and neutral sites. Therefore, bumblebees leave behind general chemical footprints everywhere they walk and we propose that they learn to use these footprints in a manner that ultimately enhances their fitness, for example, to improve their foraging efficiency and locate their nest. Experimentally, distinguishing these two modes of information transfer is crucial for understanding how they interact to shape animal behaviour and what chemical bouquets are under natural selection. Handling Editor: Heikki Hokkanen     

Evidence for mutualism between a flower-piercing carpenter bee and ocotillo: use of pollen and nectar by nesting bees

Abstract.

• 1 Carpenter bees (Xylocopa californica arizonensis) in west Texas, U.S.A., gather pollen and ‘rob’ nectar from flowers of ocotillo (Fouquieria splendens). When common, carpenter bees are an effective pollen vector for ocotillo. We examined ocotillo's importance as a food source for carpenter bees.
• 2 The visitation rate of carpenter bees to ocotillo flowers in 1988 averaged 0.51 visits/flower/h and was 4 times greater than that of queen bumble bees (Bombus pennsylvanicus sonorus), the next most common visitor. Nectar was harvested thoroughly and pollen was removed from the majority of flowers. Hummingbird visits were rare.
• 3 Pollen grains from larval food provisions were identified from sixteen carpenter bee nests. On average, 53% of pollen grains sampled were ocotillo, 39% were mesquite (Prosopis glandulosa), and 8% were Zygophyllaceae (Larrea tridentata or Guaiacum angustifolium). Carpenter bee brood size averaged 5.8 per nest.
• 4 We measured the number of flowers, and production of pollen and nectar per flower by mature ocotillo plants, as well as the quantity of pollen and sugar in larval provisions. An average plant produced enough pollen and nectar sugar to support the growth of eight to thirteen bee larvae. Ocotillo thus has the potential to contribute significantly to population growth of one of its key pollinators.
• 5 Although this carpenter bee species, like others, is a nectar parasite of many plant species, it appears to be engaged in a strong mutualism with a plant that serves as both a pollen and as a nectar source during carpenter bee breeding periods.

     

Wildflower plantings on fruit farms provide pollen resources and increase nesting by stem nesting bees

1. Wildflower plantings on farms have been shown to attract foraging wild bees, however, whether these added floral resources increase nesting densities of bees remains largely untested.
2. We placed nest boxes containing natural reeds at 20 fruit farms in Michigan. We then compared nesting densities between farms with and without wildflower plantings and analysed nest provisions to evaluate use of wildflower plantings for brood provisioning.
3. We found significantly greater nesting at farms with wildflower plantings, with only one out of 236 completed nests at a farm without a planting. The majority of nests were completed by Megachile pugnata, with a portion of nests completed by Osmia caerulescens.
4. We found that nesting bees collected pollen from only a subset of the available flowers in the wildflower plantings, with a strong preference for Centaurea maculosa, and Rudbeckia type pollens. While these species were found growing in the plantings, only Rudbeckia type species were seeded in the plantings.
5. This study provides evidence that wildflower plantings (though not only seeded species) are filling a critical resource gap for stem-nesting bees in agricultural landscapes and likely support local populations.

     

Short-term effects of experimental boreal forest &;logging disturbance on bumble bees,bumble &;bee-pollinated flowers and the bee–flower match

This study examines how, over the short term, logging affects the density of bumble bees (Apidae: Bombus), the understory plants commonly visited by bumble bees, and the numerical relationship between bumble bees and flowers. In the summers before and after winter logging, bumble bees and plants were surveyed in 50 deciduous stands (each of 8–10 ha) in the boreal forest of northern Alberta, Canada. Logging was replicated at three different intensities: 0, 10–20, and 50–75% of trees remaining. There were generally more bumble bees, species of bumble bee-visited plants, and flowers in moderately (50–75%) logged sites, but this pattern depended on the time of year. Before logging, bumble bees matched resources according to an ideal free distribution (IFD). Logging affected the distribution of bumble bees across floral resources: the slope of the regression relating bumble bee and flower proportions was less than one for clearcut and control treatments (i.e., undermatching), with too many bumble bees in the flower-poor compartments and too few in the flower-rich ones. Deviations from an IFD were negative in control sites, such that fewer bumble bees occurred here than warranted by flower numbers. Controlling for flower density, bumble bee density was significantly greater in clearcuts than in the other treatments. By disproportionately visiting plants in clearcuts (relative to flower density), and by undermatching, bumble bees in clearcuts should experience higher levels of competition. Conversely, the fewer (and undermatching) bumble bees in control sites (relative to flower abundances there) may cause these plants to obtain diminished pollination service. The proximity of clearcut logging to pristine areas may therefore negatively impact plants and bumble bees in the pristine areas, at least in the season immediately following logging.     

Pollination ofEchinocereus fasciculatus andFerocactus wislizenii

One of the most common types of cactus flower in the southwestern United States is the large, colorful, cup-shaped flower.Echinocereus fasciculatus var.boyce-thompsonii in Arizona is a representative of this class of flowers. Its flowers are visited by three common types of insect visitors: medium-sized bees, small solitary bees, and beetles. All three types of visitors come into contact with the pollen, but only the mediumsized bees regularly touch the stigma in their visitations. The main effective pollinators are therefore the medium-sized bees (Megachile, etc.).Ferocactus wislizenii has a similar floral mechanism and is likewise pollinated mainly by medium-sized bees (Megachile, Lithurge, Diadasia, etc.).Pollination of North American Cacti, 1.     

Foraging behavior of three bee species in a natural mimicry system: female flowers which mimic male flowers in Ecballium elaterium (Cucurbitaceae)

Summary The behavior of Apis mellifera and two species of solitary bees which forage in the flowers of monoecious Ecballium elaterium (L.) A. Rich (Cucurbitaceae) were compared. The female flowers of E. elaterium resemble male flowers visually but are nectarless, and their number is relatively smaller. Apis mellifera was found to discriminate between the two genders and to pay relatively fewer visits to female flowers (mean of 30% relative to male flowers) from the beginning of their activity in the morning. The time spent by honeybees in female flowers is very short compared to that spent in male flowers. It is surmised that the bees remember the differences between the flowers where they foraged on the previous days. In contrast, the two species of solitary bees Lasioglossum politum (Morawitz) (Halictidae) and Ceratina mandibularis Fiese (Anthophoridae) visit the female flowers with nearly equal frequencies at the beginning of each foraging day and stay longer in these flowers. Over the day there is a decline in the relative frequency of visits to female flowers and also in the mean time spent in them. The study shows that bees can collect rewards at high efficiency from the flowers of Ecballium elaterium because of their partial discrimination ability and the scarcity of the mimic flowers. It is suggested that the memory pattern of some solitary bees may be different from that of Apis mellifera. It seems that the limited memory and discrimination ability of bees can lead to a high frequency of visits to the mimic flowers during a long flowering season.     

COMPETITION BETWEEN HERMIT HUMMINGBIRDS PHAETHORNINAE AND INSECTS FOR NECTAR IN A COSTA RICAN RAIN FOREST

Hummingbirds in the tropical rainforests of southwestern Costa Rica face intense competition from stingless bees Trigona that steal nectar from hummingbird flowers. Here we document both interference and exploitative competition between bees and hummingbirds at scarlet, hummingbird pollinated flowers of Passiflora vitifolia. Aggressive stingless bees prevented Long-tailed Hermit Hummingbirds Phaethornis superciliosus from feeding at nearly one-third of the passion flowers approached. In exclusion experiments, bees and hummingbirds each removed most of the nectar from treated flowers. Experimental exclusion of bees also increased hummingbird use of both natural and artificial flowers.     

Long Tongues and Loose Niches: Evolution of Euglossine Bees and Their Nectar Flowers1

I examined relationships between tongue length of orchid bees (Apidae: Euglossini) and nectar spur length of their flowers in the genera Calathea, Costus, and Dimerocostus using phylogenetically independent contrasts. Long‐tubed flowers have specialized on one or several species of long‐tongued euglossine bees, but long‐tongued bees have not specialized on long‐tubed flowers. Whereas long tongues may have evolved to provide access to a wider variety of nectar resources, long nectar spurs may be a mechanism for flowers to conserve nectar resources while remaining attractive to traplining bee visitors.     

Displays of the Honeyeater Manorina melanocephala

Investigated displays of Noisy Miners, Manorina melanocephala, in Australia. This unusual bird lives in colonies and many ♂♂ care for the offspring of each ♀ flight displays, 11 non-flight displays, and several components of facial displays (including a variable eye patch) are described. The eye patch provides a large yellow and black augmented eye, important in intimidation. No stereotyped sequence of courtship behaviour precedes copulation. Displays are used to advertise nest locations. A greeting display, the corrohoree, is extremely common. The possibility of the evolution of submissive display from threat is discussed. Special vocalisations of ♂♂ and ♀♀ are use in a duet. The maintenance of bonds among many individuals in a colony may be more important than strong pair bonds. Group cohesion is probably maintained by flight display, nest display, mobbing, and other communal activities. High interspecific aggression results in few resident species in colonies. This level of interspecific aggression might be maintained by incorporating much intraspecific mimetic display and ritualised submissive behaviour.