Individual Variation in Male Pheromone Production in Xylocopa sonorina Correlates with size and Gland Color.

Sex pheromones are species-specific chemical signals that facilitate the location, identification, and selection of mating partners. These pheromones can vary between individuals, and act as signals of mate quality. Here, we investigate the variation of male pheromones in the mesosomal glands of the large carpenter bee Xylocopa sonorina, within a Northern California population. We tested the hypothesis that morphological traits are correlated with the observed variation in chemical blend composition of these bees. We also conducted behavioral assays to test whether these male pheromones act as long-range attractants to conspecifics. We found that larger males with darker mesosomal glands have a higher pheromone amount in their glands. Our analysis also suggests that this pheromone blend functions as a long-range attractant to both males and females. We show that both male body size and sexual maturation are important factors influencing pheromone abundance, and that this pheromone blend acts as a long-range attractant. We hypothesize that this recorded variation in male pheromone could be important for female choice.

Brawls Bring Buzz: Male Size Influences Competition and Courtship in Diadasia rinconis (Hymenoptera: Apidae).

Sexual selection on male body size in species with a female-biased sexual size dimorphism is common yet often poorly understood. In particular, in the majority of bee species, the relative contribution of intrasexual competition and female choice to patterns of male body size is unknown. In this field study, we examined two possible components of male mating success with respect to body size in the solitary bee Diadasia rinconis Cockerell (Hymenoptera: Apidae): 1) ability to procure a mate and 2) the duration of copulation. We found that larger males were better able to procure mates and copulated for shorter periods of time. Although consistent with sperm competition theory, differences in copulation duration were slight; possibly, the shorter copulations of larger males instead reflect in copulo female choice. Consistent with this notion, males engaged in complex courtship while mounted, characterized for the first time in any bee in such detail via audio recordings and high-speed, high-definition video. The number of pulses in male courtship behavior was also positively associated with copulation duration and may have stimulated females to continue copulating, thereby potentially allowing smaller males to transfer a full ejaculate. Females were shown to be potentially polyandrous and although we did not observe precopulatory rejection in the field, captive females frequently rejected copulation attempts by captive males. Our work indicates that intrasexual competition selects for increased body size in a solitary bee.

Organ-specific volatiles from Sonoran desert Krameria flowers as potential signals for oil-collecting bees.

The evolution of flowers that offer oils as rewards and are pollinated by specialized bees represents a distinctive theme in plant-pollinator co-diversification. Some plants that offer acetylated glycerols as floral oils emit diacetin, a volatile by-product of oil metabolism, which is utilized by oil-collecting bees as an index signal for the presence of floral oil. However, floral oils in the genus Krameria (Krameriaceae) contain ß-acetoxy-substituted fatty acids instead of acetylated glycerols, making them unlikely to emit diacetin as an oil-bee attractant. We analyzed floral headspace composition from K. bicolor and K. erecta, native to the Sonoran Desert of southwestern North America, in search of alternative candidates for volatile index signals. Using solid-phase microextraction, combined with gas chromatography-mass spectrometry, we identified 26 and 45 floral volatiles, respectively, from whole flowers and dissected flower parts of these two Krameria species. As expected, diacetin was not detected. Instead, ß-ionone emerged as a strong candidate for an index signal, as it was uniquely present in dissected oil-producing floral tissues (elaiophores) of K. bicolor, as well as the larval cells and provisions from its oil-bee pollinator, Centris cockerelli. This finding suggests that the floral oil of K. bicolor is perfused with ß-ionone in its tissue of origin and retains the distinctive raspberry-like scent of this volatile after being harvested by C. cockerelli bees. In contrast, the elaiophores of K. erecta, which are not thought to be pollinated by C. cockerelli, produced a blend of anise-related oxygenated aromatics not found in the elaiophores of K. bicolor. Our findings suggest that ß-ionone has the potential to impact oil-foraging by C. cockerelli bees through several potential mechanisms, including larval imprinting on scented provisions or innate or learned preferences by foraging adults.

Global patterns and drivers of buzzing bees and poricidal plants.

Foraging behavior frequently plays a major role in driving the geographic distribution of animals. Buzzing to extract protein-rich pollen from flowers is a key foraging behavior used by bee species across at least 83 genera (these genera comprise ∼58% of all bee species). Although buzzing is widely recognized to affect the ecology and evolution of bees and flowering plants (e.g., buzz-pollinated flowers), global patterns and drivers of buzzing bee biogeography remain unexplored. Here, we investigate the global species distribution patterns within each bee family and how patterns and drivers differ with respect to buzzing bee species. We found that both distributional patterns and drivers of richness typically differed for buzzing species compared with hotspots for all bee species and when grouped by family. A major predictor of the distribution, but not species richness overall for buzzing members of four of the five major bee families included in analyses (Andrenidae, Halictidae, Colletidae, and to a lesser extent, Apidae), was the richness of poricidal flowering plant species, which depend on buzzing bees for pollination. Because poricidal plant richness was highest in areas with low wind and high aridity, we discuss how global hotspots of buzzing bee biodiversity are likely influenced by both biogeographic factors and plant host availability. Although we explored global patterns with state-level data, higher-resolution work is needed to explore local-level drivers of patterns. From a global perspective, buzz-pollinated plants clearly play a greater role in the ecology and evolution of buzzing bees than previously predicted.

Symbiotic bacteria and fungi proliferate in diapause and may enhance overwintering survival in a solitary bee.

Host-microbe interactions underlie the development and fitness of many macroorganisms, including bees. Whereas many social bees benefit from vertically transmitted gut bacteria, current data suggests that solitary bees, which comprise the vast majority of species diversity within bees, lack a highly specialized gut microbiome. Here, we examine the composition and abundance of bacteria and fungi throughout the complete life cycle of the ground-nesting solitary bee Anthophora bomboides standfordiana. In contrast to expectations, immature bee stages maintain a distinct core microbiome consisting of Actinobacterial genera (Streptomyces, Nocardiodes) and the fungus Moniliella spathulata. Dormant (diapausing) larval bees hosted the most abundant and distinctive bacteria and fungi, attaining 33 and 52 times their initial copy number, respectively. We tested two adaptive hypotheses regarding microbial functions for diapausing bees. First, using isolated bacteria and fungi, we found that Streptomyces from brood cells inhibited the growth of multiple pathogenic filamentous fungi, suggesting a role in pathogen protection during overwintering, when bees face high pathogen pressure. Second, sugar alcohol composition changed in tandem with major changes in fungal abundance, suggesting links with bee cold tolerance or overwintering biology. We find that A. bomboides hosts a conserved core microbiome that may provide key fitness advantages through larval development and diapause, which raises the question of how this microbiome is maintained and faithfully transmitted between generations. Our results suggest that focus on microbiomes of mature or active insect developmental stages may overlook stage-specific symbionts and microbial fitness contributions during host dormancy.

Microbes, the 'silent third partners' of bee-angiosperm mutualisms.

While bee-angiosperm mutualisms are widely recognized as foundational partnerships that have shaped the diversity and structure of terrestrial ecosystems, these ancient mutualisms have been underpinned by 'silent third partners': microbes. Here, we propose reframing the canonical bee-angiosperm partnership as a three-way mutualism between bees, microbes, and angiosperms. This new conceptualization casts microbes as active symbionts, processing and protecting pollen-nectar provisions, consolidating nutrients for bee larvae, enhancing floral attractancy, facilitating plant fertilization, and defending bees and plants from pathogens. In exchange, bees and angiosperms provide their microbial associates with food, shelter, and transportation. Such microbial communities represent co-equal partners in tripartite mutualisms with bees and angiosperms, facilitating one of the most important ecological partnerships on land.

The evolution of floral sonication, a pollen foraging behavior used by bees (Anthophila).

Over 22,000 species of biotically pollinated flowering plants, including some major agricultural crops, depend primarily on bees capable of floral sonication for pollination services. The ability to sonicate ("buzz") flowers is widespread in bees but not ubiquitous. Despite the prevalence of this pollinator behavior and its importance to natural and agricultural systems, the evolutionary history of floral sonication in bees has not been previously studied. Here, we reconstruct the evolutionary history of floral sonication in bees by generating a time-calibrated phylogeny and reconstructing ancestral states for this pollen extraction behavior. We also test the hypothesis that the ability to sonicate flowers and thereby efficiently access pollen from a diverse assemblage of plant species, led to increased diversification among sonicating bee taxa. We find that floral sonication evolved on average 45 times within bees, possibly first during the Early Cretaceous (100-145 million years ago) in the common ancestor of bees. We find that sonicating lineages are significantly more species rich than nonsonicating sister lineages when comparing sister clades, but a probabilistic structured rate permutation on phylogenies approach failed to support the hypothesis that floral sonication is a key driver of bee diversification. This study provides the evolutionary framework needed to further study how floral sonication by bees may have facilitated the spread and common evolution of angiosperm species with poricidal floral morphology.

Floral biology of the saguaro (Cereus giganteus) : I. Pollen harvest by Apis mellifera.

A saguaro cactus (Cereus giganteus) produces an average of 295 flowers per season, each of which produces 286 mg fresh weight of pollen and 543 mg of nectar containing 24% sugar. At 7600 pollen grains/mg pollen, the yearly output per saguaro plant is 6.4×108 grains. Based on the measured saguaro density of 6.56 plants/ha, 553 g/ha of pollen is produced yearly. The enormous variation among individual plants in terms of flower numbers and floral bloom patterns is documented.Honey bees (Apis mellifera L.), the main collectors of saguaro pollen, collect an average of 12.2 mg pollen per foraging trip and can thus harvest 23.5 pollen loads from one flower. An average honey bee colony collects 290 g of saguaro pollen over the season, which is 24.4% of their total intake. Individual colonies exhibit wide variation in pollen collecting activities with some closely tracking the pollen resource and others almost totally ignoring it. The average for seven colonies indicates that even though variation is great the overall trend is toward closely tracking and exploiting the saguaro pollen resource. Based on the pollen productivity of saguaro and a hypothetical 90% pollen harvesting efficiency of bees, the pollen harvest potential of the saguaro environment is 1.72 colony equivalents of pollen/ha and 0.5/ha for saguaro alone. This is the first quantitative reporting of the total pollen productivity and pollen resource utilization for any plant and an opportunistic pollinator.

Bees assess pollen returns while sonicating Solanum flowers.

Can 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.

Nectar selection by Melipona and Apis mellifera (Hymenoptera: Apidae) and the ecology of nectar intake by bee colonies in a tropical forest.

Colony foraging activity of four Melipona species (Apidae: Meliponinae, tribe Meliponini) was studied during the dry season, when many plants flower in central Panama. The efficiency of sucrose solution uptake by Melipona was compared to that of domesticated European Apis mellifera. Dynamics of nectar foraging were also recorded for 3 of the Melipona visiting the forest shrub, Hybanthus prunifolius (Violaceae). 1. Sugar concentration in nectar brought to nests averaged from 21 to 60% sugar for 15 colonies of M. fasciata, M. compressipes triplaridis, M. fuliginosa and M. marginata micheneri. Concentrations ranged from 19 to 72%, and all species collected nectars ranging at least between 24 and 63% sugar. However, M. compressipes and M. marginata preferred higher concentrations and foraged less on dilute nectars. Peak colony nectar harvest occured in late morning or early afternoon; peak pollen harvest was in early morning. 2. Imbibing rates of bees given 20, 30, 45, 60 or 70% sucrose solutions were highest at ≦45% sucrose, but caloric intake was most rapid at 60% sucrose for all species. All but M. marginata displayed greater net intake rates than domesticated European Apis mellifera. A foraging choice model incorporating caloric reward and imbibing rates of bees suggests M. compressipes and M. marginata should specialize on richer nectars. Rate of caloric intake per forager weight was higher for all Melipona (0.03-0.13g) than for A. mellifera (0.10 g). 3. The nectar of Hybanthus prunifolius (Violaceae), a shrub pollinated exclusively by Melipona, progressed from 35 to 60% sugar during the day. Bees foraged most when nectar was below 60% concentration, a pattern best explained as the result of intercolony competition and greater availability of lower quality nectar. 4. Sugar concentration in nectar harvested by colonies rose from lower to higher values through the day for Melipona. The increasing caloric reward of nectar is adaptive in exploiting foraging preferences of such bees. As standing nectar crop is depleted by competing bees, a gradual shift to more rewarding nectar should promote increased bee foraging range, more flower visits during a foraging trip, floral constancy, and genetic outcrossing. 5. The nectar load capacity of A. mellifera is greater than that of Melipona. Other factors being equal, Africanized A. mellifera, now a permanent resident of neotropical forests, should visit more flowers during a foraging trip. Additional species differences in foraging behavior are analyzed.

Moths on the Flatbed Scanner: The Art of Joseph Scheer.

During the past decade a few artists and even fewer entomologists discovered flatbed scanning technology, using extreme resolution graphical arts scanners for acquiring high magnification digital images of plants, animals and inanimate objects. They are not just for trip receipts anymore. The special attributes of certain scanners, to image thick objects is discussed along with the technical features of the scanners including magnification, color depth and shadow detail. The work of pioneering scanner artist, Joseph Scheer from New York's Alfred University is highlighted. Representative flatbed-scanned images of moths are illustrated along with techniques to produce them. Collecting and preparing moths, and other objects, for scanning are described. Highlights of the Fulbright sabbatical year of professor Scheer in Arizona and Sonora, Mexico are presented, along with comments on moths in science, folklore, art and pop culture. The use of flatbed scanners is offered as a relatively new method for visualizing small objects while acquiring large files for creating archival inkjet prints for display and sale.

THE AERODYNAMICS OF POLLEN CAPTURE IN TWO SYMPATRIC EPHEDRA SPECIES.

Wind-tunnel analyses of the behavior of airborne pollen around ovules of two Ephedra species (E. trifurca and E. nevadensis) indicate that at certain airflow speeds (0.5 m/sec and 1.0 m/sec) each species is capable of biasing pollination in favor of conspecific pollen. A computer procedure was designed to evaluate the physical basis for this aerodynamic discrimination. This procedure indicates that differences in size and density confer significantly different inertial properties to the two pollen species. Operating within the specific aerodynamic environments generated around ovules from each species, these differences are sufficient to account for the biases observed in the probability of pollination. Within natural populations, there exists significant variation in pollen size (and possibly in density). Accordingly, it is possible that, under certain ambient wind conditions, ovules from each species can select subsets of the entire airborne population of Ephedra pollen.