Stephen L. Buchmann

What governs protein content of pollen: Pollinator preferences, pollen-pistil interactions, or phylogeny?

Pollen ranges from 2.5% to 61% protein content. Most pollen proteins are likely to be enzymes that function during pollen tube growth and subsequent fertilization, but the vast range of protein quantity may not reflect only pollen–pistil interactions. Because numerous vertebrate and invertebrate floral visitors consume pollen for protein, protein content may influence floral host choice. Additionally, many floral visitors pollinate their host plants. If protein content influences pollinator visitation, then pollinators are hypothesized to select for increased protein content of host plants. We analyzed or gleaned from the literature crude pollen protein concentrations of 377 plant species from 93 plant families. Using this database, we compared pollen protein concentration with (1) pollination mode, (2) pollen collection by bees, and (3) distance from stigma to ovule, after accounting for phylogeny through paired phylogenetic comparisons and a nested ANOVA including taxonomic rank. We found that pollen pr...

MALE MATING STRATEGIES IN THE BEE CENTRIS PALLIDA FOX (ANTHOPHORIDAE: HYMENOPTERA)

Males of the solitary bee Centris pallida practice one of two alternative mate-location strategies, either searching emergence areas for sites at which to dig up virgin females, or hovering by shrubs and trees, waiting for the arrival of airborne virgin females. The size of the male is related to which of these strategies he adopts, with the larger males more commonly patrolling and digging and the smaller males more commonly hovering. Large males are superior in competitive disputes over digging sites and appear to enjoy much greater reproductive success than males at the lower end of the spectrum of size. Despite this, large males are relatively rare in the population as a whole. Selection acts on females with respect to how they divide their total investment in male offspring. We examine the possibility that females which provision a number of small cells (thus producing several small males) may be as fit as or fitter than females that divide their investment into relatively few packets and produce a few large males.

Behavior and Phenology of a Specialist Bee (Dieunomia) and Sunflower (Helianthus) Pollen Availability

The phenological relationships between nesting behavior of a specialist, solitary bee, Dieunomia triangulifera, and the flowering of its primary pollen source, Helianthus annuus, were studied for 3 yr at a site in northeastern Kansas, which contained between 50 000 and >150 000 nests. Activity patterns of D. triangulifera are closely synchronized with pollen availability on nearby sunflower plants in three ways: (1) each year, D. triangulifera became active within days of the beginning of the local sunflower bloom, and the emergence schedule of the entire population at the nest site was timed such that all females had constructed nests and were collecting pollen at peak bloom; (2) over a season the greatest numbers of provisioning females were active at peak bloom, when pollen was most abundant; and (3) over the day, females made more trips, each of which took less time when pollen was most abundant on nearby flowers than when it was scarce. Between seasons, female reproductive success varied positively with the availability of H. annuus pollen. When pollen was abundant, and the population at the nest site was low, °3 times more cells were provisioned than the following year when the bee population was high and pollen abundance declined. Furthermore, 20 pollen—collecting bee species (10 specialists and 10 generalists), besides D. triangulifera, used an estimated 68% of the available sunflower pollen at this site. These data suggest that resource limitation is important in shaping patterns of provisioning behavior in D. triangulifera. Other behaviors presumably related to reproductive success were variable and suggest resources were not limiting: (1) all females did not forage on each day, even at peak bloom; (2) variance in both trip durations and the numbers of trips made per day was large; and (3) females produced far fewer eggs in their lifetime than apparently possible. We suggest that the apparently conflicting evidence for resource limitation may be explained by a physiological limit on the rate of egg production; in such a case, the effects of resource limitation, while clearly important, might not be the primary factor limiting reproductive output. Female D. triangulifera benefit by being synchronized with their resource. Daily and seasonal synchrony enable females to collect a greater amount of pollen during shorter foraging trips. The translates into higher mean reproductive success and, at the population level, allows more females to be supported by the pollen produced from nearby plants. In short, those females that are synchronized with the sunflower bloom effectively increase their own resource availability. This phenomenon may be general, especially in short—lived organisms, i.e ., the evolution of specialization may be associated with fitness benefits based on synchrony with a preferred food source.

Competition for Nectar between Introduced Honey Bees and Native North American Bees and Ants

Previous studies (Schaffer et al. 1979) of introduced honey bees foraging at Agave schottii Engelm. flowers suggest that Apis preferentially exploits the most productive patches of flowers and thereby reduces the standing crop of available nectar and the utilization of these sites by native bees. In the present paper, we report the results of experiments undertaken to evaluate this hypothesis. A single 1-ha site was studied. Visitation rates by Apis and native bees were determined, as were rates of nectar secretion and amounts of nectar available to the bees. Nectar available to bees was increased by excluding ants, which foraged on the stalks both during the day and at night. A. schottii flowers secrete 90% of their nectar at night. Prior to this exclusion, ants consumed =85% of the nightly accumulation. At first, the ants were excluded from only 10 flower stalks out of 130. These stalks were visited by greater numbers of both honey bees and bumble bees than were the controls. The experimental stalks also had higher standing crops of available nectar. Next, ants were excluded from all of the stalks on and surrounding the study site by treating them with Tree Tangle- foot. Following this manipulation the number of honey bees again increased, but the numbers of Bombus remained at the level of the controls of the first experiment. A significant increase in the numbers of small solitary bees on the stalks was also observed. These species generally foraged later in the day than Apis and Bombus, which were both active primarily early in the morning and before dusk. During these manipulations, two hives of Cordovan honey bees, a light-colored strain of Apis mellifera, were present on the site. The subsequent introduction of two additional hives had no discernible effect on the number of honey bees visiting the flowers. The final experiment consisted of removing the Cordovan hives. Thereafter the number of darker feral honey bees observed on the flowers increased until it approached the previous combined total of Cordovans (:75% of the total) and ferals. Concomitantly, the numbers of Bombus and small solitary bees first increased and then declined.

Bees assess pollen returns while sonicating Solanum flowers

SummaryCan bees accurately gauge accumulating bodily pollen as they harvest pollen from flowers? Several recent reports conclude that bees fail to assess pollen harvest rates when foraging for nectar and pollen. A native nightshade (Solanum elaeagnifolium Cavanilles) that is visited exclusively for pollen by both solitary and social bees (eg. Ptiloglossa and Bombus) was studied in SE Arizona and SW New Mexico. The flowers have no nectaries. Two experiments were deployed that eliminated “pollen feedback” to the bees by experimentally manipulating flowers prior to bee visits. The two methods were 1) plugging poricidal anthers with glue and 2) emptying anthers of pollen by vibration prior to bee visitation. Both experiments demonstrated that bees directly assess pollen harvest on a flower-by-flower basis, and significantly tailor their handling times, number of vibratile buzzes per flower and grooming bouts according to the ongoing harvest on a given flower. In comparison to experimental flowers, floral handling times were extended for both Bombus and Ptiloglossa on virgin flowers. Greater numbers of intrafloral buzzes and numbers of times bees groomed pollen and packed it into their scopae while still on the flower were also more frequent at virgin versus experimental flowers. Flowers with glued andreocia received uniformly brief visits from Bombus and Ptiloglossa with fewer sonications and virtually no bouts of grooming. Curtailed handling with few buzzes and grooms also characterized visits to our manually harvested flowers wherein pollen was artificially depleted. Sonicating bees respond positively to pollen-feedback while harvesting from individual flowers, and therefore we expect them to adjust their harvesting tempo according to the currency of available pollen (standing crop) within Solanum floral patches.

Trumpet Flowers of the Sonoran Desert: Floral Biology of Peniocereus Cacti and Sacred Datura

The floral biology of night‐blooming Peniocereus cacti and Datura plants was studied in North Americas Sonoran Desert. In populations of two rare cactus species (Peniocereus greggii and Peniocereus striatus), individual plants bloom synchronously on less than five nights per year and are self‐incompatible. In contrast, the abundant Datura discolor and Datura wrightii bloom nearly continuously from spring to autumn and are self‐compatible. Flowers of all species studied are visited by hawk moths at dusk and by honeybees and native bees the following morning. Hawk moths have the appropriate behavior and body dimensions to pollinate Peniocereus effectively, but visits are rare. Nonnative honeybees also visit P. greggii and may contribute incrementally to fruit set. Peniocereus and Datura flowers are highly reflective at all wavelengths above 400 nm but lack UV reflectance or contrast. All species studied secrete 10–80 μL of sucrose‐rich nectar within flared corollas so deep that moths must land within them, ensuring pollen carriage. These flowers provide rich energetic resources for hawk moths because the caloric content of a single flower would support from 3 to 20 min of hovering flight. Floral scents were more species specific than visual cues because D. discolor and D. wrightii emit complex blends of terpenoid, benzenoid, aliphatic, and nitrogenous scent compounds, whereas flowers of P. greggii produce only eight benzenoid compounds (all of which are present in Datura species) and Peniocereus striatus is scentless. Peniocereus cacti may benefit from sequential mutualism with the more abundant Datura species by way of pollinators nurtured as larvae by Datura foliage and as adults by Datura floral nectar.

Thermoregulatory physiology of the carpenter bee,Xylocopa varipuncta

SummaryThe carpenter beesXylocopa varipuncta maintain thoracic temperatures of 33.0°C to 46.5°C during continuous free flight from 12°C to 40°C. Since the thoracic temperature excess is not constant (decreasing from 24°C at low air temperatures to 6°C at high) the bees are thermoregulating. We document physiological transfer of relatively large amounts of heat to the abdomen and to the head during pre-flight warm-up and during artificial thoracic heating. Most of the temperature increase of the head is due to passive conduction, while that of the abdomen is due to active physiological heat transfer despite a series of convolutions of the aorta in the petiole that anatomically conform to a counter-current heat exchanger. Although the thermoregulatory mechanisms during flight are far from clarified, our data suggest that thermoregulation involves a strong reliance on active convective cooling through increased flight speed.

Time of drone flight in four honey bee species in south-eastern Thailand

SUMMARYAt Chanthaburi, Thailand, four species of Apis, A. andreniformis, A. florea, A. cerana and A. dorsata, are sympatric. Observations were carried out on three wild colonies of each species on various days in February 1992. The daily drone flight periods were only partially specific: A. andreniformis from 12.15 h to 13.45 h; A. florea from 14.00 h to 16.45 h; A. cerana from 15.15 h to 17.30 h; and A dorsata from 18.15 h to 18.45 h. The significance of these partially separate drone flight periods is discussed in terms of both reproductive isolation and evolution.

Pollen digestion and nitrogen utilization by Apis mellifera L. (Hymenoptera: Apidae)

Abstract 1. 1. The apparent digestibility (AD) of pollen by Apis mellifera is 89% by gravimetric analysis and 77% as determined by ue of Cr 2 O 3 , an internal marker placed in the diet. 2. 2. The average weight of nitrogen consumed per individual over a 28-day period was 3.07 mg, of which 0.60 mg is defecated in the form of 86.2% undigested food and 13.8% uric acid. 3. 3. The coefficient of apparent digestibility of nitrogen (CADN) of pollen is 83% by gravimetric analysis, and 72% by use of the Cr 2 O 3 marker technique. 4. 4. A. mellifera efficiently digests and utilizes both the food substance and nitrogen of pollen, the natural diet of the species.

The plight of pollinating bees

Pollinating animals (mostly bats, bees, beetles, birds, butterflies, flies, moths and wasps) provide almost incalculable economic and ecological benefits to humans, flowering plants and wildlife. Bees are the worlds dominant pollinators, as the approximately 17 000 known bee species 7 collectively interact with most of the planets quarter million angiosperm species. Animal pollination by bees and other insects is the first step in the flowering/fruiting process resulting in the production of vegetables and fruits containing viable seeds, essential nutrition comprising roughly 35% of the human diet. 2 Recent statements suggest we may be losing pollinators and their ecological services on a global scale, due to habitat destruction and other causes, and could face a crisis in agricultural pollination.