Floral differentiation among insular and mainland populations of Weigela coraeensis (Caprifoliaceae)

We compared the floral morphologies, floral scents, and flower visitor compositions of Weigela coraeensis var. coraeensis on the Japanese mainland and its variety fragrans endemic to the Izu Islands to examine the differentiation process of W. coraeensis var. fragrans. The corolla lengths of W. coraeensis were smaller on the Izu Islands than those on the mainland and decreased gradually with the distance from the mainland, probably resulting from changes in pollinator fauna. A total of 13 volatile compounds were identified in the floral scent analyses, and limonene was produced at the highest level, although the floral scents were not different between var. coraeensis and var. fragrans. In this study, it was suggested that the pollinator fauna peculiar to the Izu Islands influenced the morphological differentiation of W. coraeensis var. fragrans.     

Temporal pattern of floral color change and time retention of post‐change flowers in Weigela japonica var. sinica (Caprifoliaceae)

Abstract Floral color changes are common in Weigela and the retention of post‐change flowers has been interpreted as a mechanism to increase attractiveness from a long distance and shorten pollinators’ lingering time on the inflorescence(s) of individual plants. In the present study, we investigated the temporal pattern of floral color change and time required for pollen tube growth in the shrub Weigela japonica var. sinica. Over the 4‐day anthesis, the color of the corolla in this species changes from white to red and the color cue changes from yellow to purple. The duration of both the white phase and the intermediate phase is approximately 1 day and the duration of the red phase is approximately 2 days. Our studies showed that color change in Weigela japonica var. sinica is age‐dependent but independent of pollinator visits and flower pollination. Post‐change flowers lost most of both the male and female residual reproductive ability and retained no rewards for pollinators. It took at least 3 days for a pollen tube to grow to the ovules and achieve fertilization. Thus, retention of post‐change flowers is necessary for the completion of pollen tube growth. Our results indicate that the temporal pattern of color change and time requirement for pollen tube growth are most likely related events.     

Floral biology of two Vanilloideae (Orchidaceae) primarily adapted to pollination by euglossine bees

Vanilloideae comprises 15 genera distributed worldwide, among which are Vanilla and Epistephium (tribe Vanilleae). Based on field and laboratory investigations, the pollination biology of V. dubia and E. sclerophyllum was analysed. The former was surveyed in a semi‐deciduous mesophytic forest at the biological reserve of Serra do Japi and in a marshy forest at the city of Pradópolis, southeastern Brazil. The latter was examined in rocky outcrop vegetation in the Chapada Diamantina, northeastern Brazil. In the studied populations, the tubular flowers of V. dubia and E. sclerophyllum were pollinated by bees. Pollen was deposited on either their scutellum (V. dubia) or scutum (E. sclerophyllum). The mentum region of V. dubia is dry, whereas that of E. sclerophyllum presents a small quantity of dilute nectar. Flowers of E. sclerophyllum are scentless, while those of V. dubia are odoriferous. Although V. dubia is self‐compatible, it needs a pollinator to produce fruit. In contrast, E. sclerophyllum sets fruit through spontaneous self‐pollination, but biotic pollination also occurs. Both species are primarily adapted to pollination by euglossine bees. Pollination by Euglossina seems to have occurred at least twice during the evolution of Vanilleae. Furthermore, shifts between rewarding and reward‐free flowers and between autogamous and allogamous species have been reported among vanillas.     

Allozyme variation in bumble bees (Hymenoptera: Apidae)

Allozyme variation at an average of 37.3 loci was assessed in queens of 16 Bombus and 2 Psithyrus bumble bee species from North America. The mean expected heterozygosity (H) for the Bombus species was 0.008 +/- 0.006 (95% confidence limits) and that for the Psithyrus was 0.007 +/- 0.007. These levels are significantly lower than found in other Hymenoptera but are comparable to those found in previous studies of bumble bees based on far fewer loci. Neutral mutation and random genetic drift can account for the observed variation, but this implies a very small effective population size for species of bumble bees.     

Isolation and characterization of microsatellite loci from Weigela coraeensis (Caprifoliaceae)

Weigela coraeensis var. coraeensis is a deciduous shrub species distributed in Japan on the mainland, Honshu, whereas its variety W. coraeensis var. fragrans is endemic to the Izu Islands located south of Honshu. We isolated eight polymorphic microsatellite loci from the species and characterized these loci for 20 individuals from a population in Honshu. The number of alleles per locus ranged from 7 to 15 and the observed and expected heterozygosities ranged from 0.60 to 0.90 and from 0.65 to 0.90, respectively. These eight polymorphic microsatellites will be useful for examining intraspecific genetic differentiation in W. coraeensis.     

Flower color change accelerated by bee pollination in Tibouchina (Melastomataceae)

Floral color changes are common among Melastomataceae and have been interpreted as a warning mechanism for bees to avoid old flowers, albeit increasing long-distance flower display. Here the reproductive systems of Tibouchina pulchra and T. sellowiana were investigated by controlled pollinations. Their pollinators were identified, and experiments on floral color and fragrance changes were conduced to verify if those changes affect the floral visitation. Both Tibouchina species are self compatible. The flowers lasted three days or more, and the floral color changed from white in the 1st day to pink in the following days. Pollen deposition on stigma induced floral color change. The effectiveness of the pollination is dependent on bees’ size; only large bees were regarded as effective pollinators. In experimental tests, the bees in T. pulchra preferred the natural white flowers while the visitors of T. sellowiana were attracted by both natural and mimetic 1st-day flowers (2nd-day flowers with experimentally attached 1st-day flower petals). During the experiments on floral fragrance, the bees visited both natural and mimetic 1st-day flowers (2nd-day flowers with 1st-day flower scents). In both experiments, the bees avoided natural 2nd-day flowers, but seldom visited modified 2nd-day flowers. The attractiveness of T. pulchra and T. sellowiana flowers cannot be attributed exclusively to the color or the fragrance separately, both factors seemingly act together.     

Floral scent chemistry within the genus Linnaea (Caprifoliaceae)

‘Beauty bush’ and ‘twin flower’ are common names attributed to two well‐recognizable species belonging to the genus Linnaea (16 spp.) – L. amabilis and L. borealis – long admired by botanists and gardeners for their perfumed paired bell‐shaped flowers. In the present study, we investigated their floral scent compositions through gas chromatography – mass spectrometry (GC‐MS) analysis of dynamic headspace samples. Because the flowers of L. borealis in wild populations are fragrant both during the day and in the evening, circadian variation of scent emission was also assessed for this species. In total, 26 chemical compounds comprise the floral scent bouquets of L. amabilis and L. borealis, identified as monoterpenes (14), benzenoids and phenylpropanoids (5), aliphatics (3), sesquiterpenes (3) and irregular terpenes (1). Whereas monoterpenes, notably (‐)‐α‐ and β‐pinene, dominated the scent of L. amabilis (over 82% relative abundance), benzene derivates: 1,4 dimethoxybenzene, anisaldehyde, 2‐phenylethanol, benzaldehyde and nicotinaldehyde were exclusive to analysed headspace samples of L. borealis, accounting for 52% to 100% of their relative compositions, in three Swedish populations. A southwestern Finnish population was characterized by the four first mentioned benzenoid compounds and large amounts of (‐)‐α‐ and β‐pinenes plus two aliphatic substances. The scent compounds identified for both species are ubiquitous and may serve as generalist attractants/stimulants for a broad assortment of anthophilous insects. The basic work on the flower scent of L. amabilis and L. borealis should inspire studies of their pollination biology, primarily the behaviour‐guiding roles of the characteristic emitted volatiles.     

A comprehensive phylogeny of the bumble bees (Bombus)

Bumble bees ( Bombus Latreille) occupy a wide diversity of habitats, from alpine meadows to lowland tropical forest, yet they appear to be similar in morphology throughout their range, suggesting that behavioural adaptations play a more important role in colonizing diverse habitats. Notwithstanding their structural homogeneity, bumble bees exhibit striking inter- and intraspecific variation in colour pattern, purportedly the outcome of mimetic evolution. A robust phylogeny of Bombus would provide the framework for elucidating the history of their wide biogeographical distribution and the evolution of behavioural and morphological adaptations, including colour pattern. However, morphological studies of bumble bees have discovered too few phylogenetically informative characters to reconstruct a robust phylogeny. Using DNA sequence data, we report the first nearly complete species phylogeny of bumble bees, including most of the 250 known species from the 38 currently recognized subgenera. Bayesian analysis of nuclear (opsin, EF-1α, arginine kinase, PEPCK) and mitochondrial (16S) sequences results in a highly resolved and strongly supported phylogeny from base to tips, with clear-cut support for monophyly of most of the conventional morphology-based subgenera. Most subgenera fall into two distinct clades ( short-faced and long-faced ) associated broadly with differences in head morphology. Within the short-faced clade is a diverse New World clade, which includes nearly one-quarter of the currently recognized subgenera, many of which are restricted to higher elevations of Central and South America. The comprehensive phylogeny provides a firm foundation for reclassification and for evaluating character evolution in the bumble bees.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 161–188.     

Floral traits mediate the vulnerability of aloes to pollen theft and inefficient pollination by bees

Background and Aims

Pollen-collecting bees are among the most important pollinators globally, but are also the most common pollen thieves and can significantly reduce plant reproduction. The pollination efficiency of pollen collectors depends on the frequency of their visits to female(-phase) flowers, contact with stigmas and deposition of pollen of sufficient quantity and quality to fertilize ovules. Here we investigate the relative importance of these components, and the hypothesis that floral and inflorescence characteristics mediate the pollination role of pollen collection by bees.

Methods

For ten Aloe species that differ extensively in floral and inflorescence traits, we experimentally excluded potential bird pollinators to quantify the contributions of insect visitors to pollen removal, pollen deposition and seed production. We measured corolla width and depth to determine nectar accessibility, and the phenology of anther dehiscence and stigma receptivity to quantify herkogamy and dichogamy. Further, we compiled all published bird-exclusion studies of aloes, and compared insect pollination success with floral morphology.

Key Results

Species varied from exclusively insect pollinated, to exclusively bird pollinated but subject to extensive pollen theft by insects. Nectar inaccessibility and strong dichogamy inhibited pollination by pollen-collecting bees by discouraging visits to female-phase (i.e. pollenless) flowers. For species with large inflorescences of pollen-rich flowers, pollen collectors successfully deposited pollen, but of such low quality (probably self-pollen) that they made almost no contribution to seed set. Indeed, considering all published bird-exclusion studies (17 species in total), insect pollination efficiency varied significantly with floral shape.

Conclusions

Species-specific floral and inflorescence characteristics, especially nectar accessibility and dichogamy, control the efficiency of pollen-collecting bees as pollinators of aloes.     

Queen-worker conflict and social parasitism in bumble bees (Hymenoptera: Apidae)

Psithyrus ashtoni (Hymenoptera: Apidae) is an obligate, workerless bumble, bee social parasite which invades nests of Bombus affinis. Although parasites are limited by host worker defence to invading very small colonies, there is considerable flexibility in the way parasites control host brood bionomics once they are accepted inside the nest. A study of 46 parasitized and 22 non-parasitized laboratory colonies of B. affinis showed that P. ashtoni females cohabited with host queens and workers while the worker force increased, but not to the maximum normally achieved in non-parasitized nests. While colony reproductive success was correlated with the number of workers reared, parasites risked being killed or ejected from the comb by workers, after the queen had lost dominance. Host bees usually succeeded in rearing offspring, and Psithyrus reproductive success was related to the ability of parasites to control proportional investment in the two species. In addition to displacing P. ashtoni females, host bees ate the eggs of parasites and ejected their larvae. These behaviours were also exhibited by workers in the later stages of development of non-parasitized colonies. These results indicate that social parasites are at least partially subject to the conflict of genetic self-interest between the queen and her workers which is believed to influence the control of reproductive investment in haplodiploid Bombus societies.     

Floral rewards and pollination in Cytiseae (Fabaceae)

 Cytiseae have been reported to be mostly nectar-lacking, yet some taxa secrete nectar from extrastaminal nectaries. We studied the pollination biology of four shrubby species of Cytiseae (Cytisophyllum sessilifolium (L.) Lang, Spartium junceum L., Genista radiata (L.) Scop., Genista cilentina Valsecchi) which differ for ecology, distribution and population size. All species resulted obliged xenogamous, insect visits being necessary for successful pollination. Bumblebees and solitary bees are the principal pollinators, but also many beetles, some hover-flies, and few bugs visit flowers. Pollinator specificity is low, and this may be the reason of the scarce seed set compared to the number of ovules. Pollen is the main reward, but traces of glucose were detected in all species, at the base of vexillum or on the reproductive column. Nectar production is irregular in time, and apparently unpredictable. We suppose that nectar may play a role in attracting pollinators determining their right position for a successful pollination. Received August 12, 2002; accepted November 25, 2002 Published online: June 2, 2003     

Temporal dynamics of facultative social parasitism in bumble bees (Hymenoptera: Apidae)

Parasitical behaviour is thought to play an important, yet so far largely unknown role in the evolution and maintenance of insect sociality. In this study, the influence of interspecific, facultative social parasitism upon bumble bee, Bombus, nesting biology was explored. Queens of B. affinis were introduced into 38 various-sized laboratory colonies of B. terricola. Foreign queens were very successful at killing the resident queen and usurping pre-worker nests (77% wins), although usurpation success decreased to 30% in colonies that contained workers. In addition, B. affinis queens were unable to suppress ovarian development in B. terricola workers that emerged prior to nest usurpation, resulting in the eventual death or expulsion of the foreign queen. In contrast, ovarian development was supporessed in workers that eclosed in the presence of a foreign queen, and in workers that were less than 5 h old when confined in small experimental boxes with a B. affinis queen. Foreign queens that usurped a nest prior to worker emergence were assisted by B. terricola workers, and achieved similar reproductive success when compared to a cohort of 22 B. affinis queens that initiated their own nests in the laboratory. These results suggest that there are periods in the ontogeny of Bombus nest defence, recognition and dominance during which bees are sensitive to the effects of nest parasitism. In bumble bees, and in other social insects, individuals of some species may exploit these weaknesses for their own reproductive benefit.     

Differential sensitivity of honey bees and bumble bees to a dietary insecticide (imidacloprid)

Currently, there is concern about declining bee populations and the sustainability of pollination services. One potential threat to bees is the unintended impact of systemic insecticides, which are ingested by bees in the nectar and pollen from flowers of treated crops. To establish whether imidacloprid, a systemic neonicotinoid and insect neurotoxin, harms individual bees when ingested at environmentally realistic levels, we exposed adult worker bumble bees, Bombus terrestris L. (Hymenoptera: Apidae), and honey bees, Apis mellifera L. (Hymenoptera: Apidae), to dietary imidacloprid in feeder syrup at dosages between 0.08 and 125 μg l^?1. Honey bees showed no response to dietary imidacloprid on any variable that we measured (feeding, locomotion and longevity). In contrast, bumble bees progressively developed over time a dose-dependent reduction in feeding rate with declines of 10–30% in the environmentally relevant range of up to 10 μg l^?1, but neither their locomotory activity nor longevity varied with diet. To explain their differential sensitivity, we speculate that honey bees are better pre-adapted than bumble bees to feed on nectars containing synthetic alkaloids, such as imidacloprid, by virtue of their ancestral adaptation to tropical nectars in which natural alkaloids are prevalent. We emphasise that our study does not suggest that honey bee colonies are invulnerable to dietary imidacloprid under field conditions, but our findings do raise new concern about the impact of agricultural neonicotinoids on wild bumble bee populations.     

蜜蜂及熊蜂微孢子虫rRNA基因研究

核糖体RNA(rRNA)是一种理想的进化计时器,已广泛地应用于研究微生物的系统发育和进化关系。蜜蜂和熊蜂都被微孢子虫感染,关于蜜蜂和熊蜂微孢子虫rRNA基因研究主要有rRNA基因序列的测定分析、二级结构的研究和用rRNA基因检测诊断微孢子虫等。这些对蜜蜂和熊蜂微孢子虫系统发育的研究和微孢子虫的防治等具有重要的推动作用。     

Bombus folsomi and the origin of Philippine bumble bees (Hymenoptera: Apidae)

Abstract The type female of Bombus folsomi (Frison) is redescribed and synomymized with B.ephippiatus Say. It is concluded that the putative type locality of B.folsomi , Mt Kinabalu in Borneo, is in error and that the genus appears to be absent from Borneo. This lends support to the hypothesis that bumble bees immigrated to the Philippines by an unusual northern route through Taiwan. More rigorous testing of this idea will require further cladistic analysis of the genus Bombus .     

Foraging errors play a role in resource exploration by bumble bees (Bombus terrrestris)

If the cognitive performance of animals reflects their particular ecological requirements, how can we explain appreciable variation in learning ability amongst closely related individuals (e.g. foraging workers within a bumble bee colony)? One possibility is that apparent ‘errors’ in a learning task actually represent an alternative foraging strategy. In this study we investigate the potential relationship between foraging ‘errors’ and foraging success among bumble bee (Bombus terrestris) workers. Individual foragers were trained to choose yellow, rewarded flowers and ignore blue, unrewarded flowers. We recorded the number of errors (visits to unrewarded flowers) each bee made during training, then tested them to determine how quickly they discovered a more profitable food source (either familiar blue flowers, or novel green flowers). We found that error prone bees discovered the novel food source significantly faster than accurate bees. Furthermore, we demonstrate that the time taken to discover the novel, more profitable, food source is positively correlated with foraging success. These results suggest that foraging errors are part of an ‘exploration’ foraging strategy, which could be advantageous in changeable foraging environments. This could explain the observed variation in learning performance amongst foragers within social insect colonies.     

Distribution of a model biocontrol agent (Serenade® MAX) in apple and pear by mason bees and bumble bees

1. Biocontrol agents (BCAs) are commonly sprayed on flowering pipfruit trees to prevent them from getting infected by various pathogens. By entomovectoring, BCAs can be directly delivered onto the flowers. However, we currently lack knowledge on the distribution dynamics of BCAs by pollinators.
2. Here, managed bees, both bumble bees (Bombus terrestris) and mason bees (Osmia bicornis and Osmia cornuta), were placed in the vicinity of flowering pipfruit trees (pear -‘Conference’, and apple—‘Svatava’ and ‘Jonagold’), and this allowed us to investigate the distribution of a model BCA, namely, Serenade® MAX, from spray-inoculated flowers of a centralized tree to non-inoculated flowers of surrounding receiver trees by bees in an experimental setup in outdoor conditions.
3. One hour after inoculation, we detected an enrichment of BCA in the flowers of the receiver trees and this for each tested pipfruit.
4. The distribution of BCA from treated to untreated flowers was homogenous between the receiver trees for ‘Svatava’, while significantly different loads were detected for both ‘Conference’ and ‘Jonagold’, which might be due to differences in environmental factors, and/or bee characteristics.
5. More research is needed to understand the distribution dynamics of BCAs by pollinators in field conditions, such as in commercial orchards or crop fields, and how this could result in an efficient control.

     

Brain biogenic amines and reproductive dominance in bumble bees (Bombus terrestris)

To begin to explore the role of biogenic amines in reproductive division of labor in social insects, brain levels of dopamine, serotonin, and octopamine were measured in bumble bee (Bombus terrestris) workers and queens that differ in behavioral and reproductive state. Levels of all three amines were similar for mated and virgin queens. Young workers that developed with or without a queen had similar amine levels, but in queenright colonies differences in biogenic amine levels were associated with differences in behavior and reproductive physiology. Dominant workers had significantly higher octopamine levels compared with workers of lower dominance status but of similar size, age, and ovary state. High dopamine levels were associated with the last stages of oocyte development irrespective of worker social status and behavior. These results suggest that biogenic amines are involved in behavioral and physiological aspects of regulation of reproduction in bumble bees. Accepted: 10 December 1999     

Phylogeny of Weigela and Diervilla (Caprifoliaceae) Based on Nuclear rDNA ITS Sequences: Biogeographic and Taxonomic Implications

Weigela and three species of Diervilla were inferred from nucleotide sequence variation in the internal transcribed spacer (ITS) regions of 18-26S nuclear ribosomal DNA. Phylogenetic trees were obtained using parsimony, distance, and maximum likelihood methods. The ITS phylogenies did not support the monophyly of Weigela, which comprises three major clades. The first clade includes a single species, W. middendorffiana, which is more closely related with American genus, Diervilla. The second clade consisted of a single species, W. maximowiczii, but its relationship to other Weigela species is equivocal. The third one is a strongly supported core clade which contains the remaining Weigela species. Within the core group, W. hortensis exhibits the most distinct ITS sequence type. The hybrid origin of the species from the putative parents, W. florida and W. subsessilis, is not supported. The ITS sequence evidence favors the taxonomic hypothesis proposed by Nakai who recognized four distinct evolutionary lines (Diervilla, Macrodiervilla, Weigelastrum and Weigela). However, recognition of the two sections, Calysphyrum and Weigela was not supported in the ITS phylogenies. Substantial morphological differences between Diervilla and Weigela middendorffiana do not support the morphological stasis concept which has been considered as a general evolutionary mode among the Asian and North American disjunct taxa. Received 27 July 1998/ Accepted in revised form 7 July 1999