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.     

Bumble bee behavior and selection on flower size in the sky pilot,Polemonium viscosum

Summary In alpine Polemonium viscosum, plants having sweet-scented flowers are primarily pollinated by queens of the bumble bee species, Bombus kirbyellus. In this paper we ask whether two aspects of the pollination effectiveness of bumble bees, visitation rate and pollination efficiency, vary significantly with flower size in sweet-flowered P. viscosum.(i) Bumble bees visited plants with large flowers on 80–90% of encounters, but visited those with smaller flowers on only 49% of encounters. (ii) However, the gain in pollination that large-flowered plants obtained via increased visitation was countered in part because bumble bees deposited fewer outcross pollen grains per visit on stigmas of large flowers than on those of small ones. When both visitation rate and pollination efficiency are taken into account, the predicted value of a single bumble bee encounter declines from 1.06 seeds for flowers larger than 18 mm in diameter to 0.55 seeds for flowers smaller than 12 mm in diameter. Our results suggest that bumble bee pollinators of P. viscosum prefer flower morphologies that are poorly suited for precise pollination. Such behavioral complexities are likely to place constraints on the evolution of optimal floral design.     

Partial preference of insects for the male flowers of an annual herb

Summary The flowers of the annual herb Impatiens capensis have distinct male and female phases. The male phase lasts four times as long as the female phase, and male flowers contain about 50% more nectar than female flowers. This suggests that the bulk of allocation to the flower is designed to ensure the dispersal of pollen rather than the fertilization of ovules. Honeybees, wasps and bumble bees all land on male flowers more often than would be expected by chance, and, having landed, wasps and bumble bees are more likely to enter a male flower than a female flower. The frequency of male flowers in the diet therefore exceeds their frequency in the population. This preference, although strong and consistent, is only partial, since some female flowers are included in the diet. We propose two hypotheses to account for the observed partial preference, the first based on competition between bees for flowers, and the second asserting that the bees detect nectar levels directly without using floral gender as a cue. The results of an experiment in which the most obvious gender cue, the androecium, was removed are consistent with the second hypothesis.     

Effects of variation in inflorescence size and floral rewards on the visitation rates of traplining pollinators ofAralia hispida

Summary In field experiments withAralia hispida inflorescences, the following variables were manipulated: number of umbels per inflorescence, number of flowers per umbel, and amounts of pollen and nectar per flower. Visitation rates by bumble bees, the principal pollinators, were then observed. In the reward-variation experiments, bees appeared to learn the positions of nectar-rich shoots, and visited them significantly more often than nectar-poor shoots. They did not respond to similar variation in pollen production. The nectar preferences developed slowly after the treatments were imposed, and bees continued to favor sites that had been occupied by nectar-rich shoots even after the treatments were discontinued. Visitation rate was approximately proportional to flower number, making it unlikely that increases in inflorescence size produced a disproportionate gain in male reproductive success (a necessary condition in certain models for the evolution of dioecy). For a fixed number of flowers per inflorescence, bees preferred inflorescences with more umbels. In pairwise choice tests of male-phase and female-phase umbels of various sizes, bees preferred male-phase umbels and larger umbels; the preference for male-phase umbels is stronger in bees that had previously fed on male-phase umbels.     

The floral biology ofThelymitra epipactoides (Orchidaceae), and the implications of pollination by deceit on the survival of this rare orchid

Thelymitra epipactoides has a highly variable visual display achieved through polychromatic flowers and variable inflorescence size, bearing between 7 and 31 flowers, which attract foraging polylectic bees. Only bees of the genusNomia were observed carrying pollinia and successfully pollinating the orchid. The genusNomia contains polylectic, pollen gathering species that store pollen in both the crop and scopa on the hind legs. The absence of a reward for the bees indicates the orchid is relying on deception to attract visitors. The relationship of deception to mimicry is discussed. Once on the flower, tactile, visual and possibly olfactory stimuli direct bees to the false anther formed by the voluminous column wings, where morphological adaptations of the flower ensure that the pollinarium is deposited on the gaster of the bee to effect pollination. — The lack of seed set observed on the Victorian coast appears to be due to the absence of pollinators from the heath and grassland communities in which the orchid grows. This may well be a consequence of the reduced number of plants flowering in the community (a result of the elimination of fire at these sites), thus not maintaining a floral community attractive to potential pollinators.     

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.     

Vectoring of Pepino mosaic virus by bumble‐bees in tomato greenhouses

Pepino mosaic virus (PepMV) has become an important viral disease of greenhouse tomatoes worldwide. The ability of bumble‐bees (Bombus impatiens), used for pollination, to acquire and transmit PepMV was investigated, and the prevalence of PepMV in plants and bumble‐bees in commercial tomato greenhouses was determined. PepMV infection in plants was determined using enzyme‐linked immunosorbent assay, while in bumble‐bees direct real‐time PCR was used. In the first experiment, the bumble‐bees were exposed for 14 days to PepMV‐infected plants. After 14 days, almost all bumble‐bees were PepMV positive both in the hive (78.5 ± 17.5%) and in the flowers (96.3 ± 3.6%). In the second experiment, bumble‐bees were released into a greenhouse with both PepMV‐infected source plants and healthy non‐infected target plants for 14 days. At the end of the experiment, 61.0 ± 19.5% of the bees collected from the hive and 83.3 ± 16.7% of the bees sampled from the flowers were PepMV positive. Bumble‐bees transmitted PepMV from the infected to the healthy non‐infected tomato plants. Two weeks after bumble‐bee release, the virus was detected in leaf, fruit and flower samples of formerly healthy plants. After 6 weeks, the percentage of PepMV positive samples from the target plants increased to 52.8 ± 2.8% of the leaves and 80.6 ± 8.4% of the fruits. In the control greenhouse without bumble‐bees, the target plants did not become infected. Based on the infection levels in flowers, fruits and leaves, the PepMV infection occurred possibly first in the pollinated flowers, and then spread from the fruit that developed from the flowers to other parts of the plant. In commercial greenhouses where PepMV was present, 92–100% of the plants and 88–100% of the bumble‐bees were PepMV positive. No infected plant samples were found in the control commercial greenhouse, but a small number of bumble‐bees (10%) tested PepMV positive.     

Division of labour within flowers: heteranthery,a floral strategy to reconcile contrasting pollen fates

In many nectarless flowering plants, pollen serves as both the carrier of male gametes and as food for pollinators. This can generate an evolutionary conflict if the use of pollen as food by pollinators reduces the number of gametes available for cross‐fertilization. Heteranthery, the production of two or more stamen types by individual flowers reduces this conflict by allowing different stamens to specialize in ‘pollinating’ and ‘feeding’ functions. We used experimental studies of Solanum rostratum (Solanaceae) and theoretical models to investigate this ‘division of labour’ hypothesis. Flight cage experiments with pollinating bumble bees (Bombus impatiens) demonstrated that although feeding anthers are preferentially manipulated by bees, pollinating anthers export more pollen to other flowers. Evolutionary stability analysis of a model of pollination by pollen consumers indicated that heteranthery evolves when bees consume more pollen than should optimally be exchanged for visitation services, particularly when pollinators adjust their visitation according to the amount of pollen collected.     

Managed bumble bees increase flower visitation but not fruit weight in polytunnel strawberry crops

Animal-mediated pollination is essential for the production and quality of fruits and seeds of many crops consumed by humans. However, crop pollination services might be compromised when wild pollinators are scarce. Managed pollinators are commonly used in crops to supplement such services with the assumption that they will enhance crop yield. However, information on the spatiotemporal pollinator-dependence of crops is still limited. We assessed the contribution of commercial bumble bee colonies compared to the available pollinator community on strawberry (‘Fortuna’ variety) flower visitation and strawberry quality across a landscape gradient of agricultural intensification (i.e. polytunnel berry crop cover). We used colonies of bumble bees in winter and in spring, i.e. when few and most wild pollinators are in their flight period, respectively. The placement of colonies increased visits of bumble bees to strawberry flowers, especially in winter. The use of bumble bee colonies did not affect flower visitation by other insects, mainly honey bees, hoverflies and other Diptera. Flower visitation by both honey bees and wild insects did not vary between seasons and was unrelated to the landscape gradient of berry crop cover. Strawberries were of the highest quality (i.e. weight) when insect-mediated pollination was allowed, and their quality was positively related to wild flower visitors in winter but not in spring. However, increased visits to strawberry flowers by managed bumble bees and honey bees had no effect on strawberry weight. Our results suggest that the pollination services producing high quality strawberry fruits are provided by the flower visitor community present in the study region without the need to use managed bumble bees.     

Attractiveness of single and multiple species flower patches to beneficial insects in agroecosystems

The provision of floral resources for the enhancement of beneficial insect populations has shown promise as a strategy to enhance biological control and pollination in agroecosystems. One approach involves the provision of a single flower species while a second involves the multiple flower species, but the two have never been compared experimentally. Here we examine the influence of single and multiple species flower treatments on the abundance and foraging behaviour of key beneficial insects in two agricultural agroecosystems (broccoli and lucerne crops). The five flower treatments comprised buckwheat only, phacelia only, a simple mixture of buckwheat and phacelia, a complex mixture of buckwheat, phacelia and a commercial seed blend or the existing crop as a control. The abundance of bumble‐bees (Bombus hortorum) and honey bees (Apis mellifera) was highest in the three treatments that contained phacelia, while hoverfly (Melanostoma fasciatum) numbers were high in all four flower treatments. Bumble‐bees and honey bees probed almost exclusively phacelia flowers, even when provided with a choice of other flower species in the simple and complex mixture treatments. In contrast, hoverflies probed the flowers of all plant species in single and multiple species treatments, with no apparent difference in acceptance. However, in mixture treatments, the majority of individual bumble‐bees, honey bees and hoverflies probed the flowers from only one species, despite the presence of alternative flower species. Our results illustrate how an appreciation of insect floral attractiveness can be used to customise the species composition of floral patches to potentially maximise biological control and pollination in targeted agroecosystems.     

Pollination mechanism in southern Brazilian orchids which are exclusively or mainly pollinated by halictid bees

The pollination process is documented in three sympatric orchids found in Curitiba, Paraná State, southern Brazil. InCampylocentrum aromaticum (Epidendroideae: Angraeciinae) andPrescottia densiflora (Spiranthoideae: Prescotiinae) halictid bees act as main pollinators with minor contributions from other insects, such as Syrphid flies. Because of the pollinarium and column structure inCyclopogon diversifolius. (Spiranthoideae, Spiranthinae), halictid bees are the only insects capable of performing pollination. In the three studied species pollinarium removal and deposition are achieved by interaction between the column and bee's mouth parts. Morphological and ecological flower features in agreement with this pollination mode are discussed and pollination by halictid bees is suggested to occur in a number of South American orchids.     

Floral color change in Weigela middendorffiana (Caprifoliaceae): reduction of geitonogamous pollination by bumble bees

We examined the significance of retaining color-changed flowers in pollination success of Weigela middendorffiana through a single visit of bumble bees. Inner parts of flowers changed color with age from yellow to red. In an investigation of the mating system, duration of each color phase, reproductive ability of each of the color-phase flowers, and the effects of color-changed flowers on bumble bee behavior (1) flowers of this species were self-incompatible, (2) color-changed flowers provided little reward to pollinators and little residual reproductive ability, (3) the timing of floral color change was delayed with the progress of flowering season within individual plants, while the duration of the red phase shortened with the progress of flowering season, and (4) red-phase flowers did not attract bumble bees at a distance but did contribute to reducing the number of successive flower visits during a single stay within the plants. Red-phase flowers seemed to indicate the low reward level of old flowers and functioned as a cue to discourage pollinators from staying longer on the same plant. Our results predict that the retention of color-changed flowers without sexual function can enhance the pollination success of a whole plant through male function by reducing successive flower visits during a single stay of pollinators, i.e., geitonogamous pollination.     

明亮熊蜂和意大利蜜蜂为温室草莓的授粉行为比较观察

蜜蜂和熊蜂都是理想的授粉昆虫,但熊蜂比蜜蜂更适合为温室果菜授粉,主要由于熊蜂和蜜蜂授粉时的活动方式不同。作者对明亮熊蜂和意大利蜜蜂为日光温室草莓授粉时的行为和活动方式进行了比较研究。结果表明,明亮熊蜂和意大利蜜蜂的授粉行为相似,但活动方式不同。明亮熊蜂开始访花的时间（8:00～8:05）比意大利蜜蜂（9:25～9:40）早,停止访花的时间（15:55～16:05）却比意大利蜜蜂（15:20～15:30）晚;开始访花的温度（12～13℃）也比意大利蜜蜂（>15℃）低,意大利蜜蜂在早晨和阴天不访花。明亮熊蜂个体的日活动时间271.43±4.48 s,明显比意大利蜜蜂个体的日活动时间180.00±2.64 s长,差异显著;而采集时间为105.71±1.16 s,显著长于意大利蜜蜂的76.43±3.83 s。明亮熊蜂每分钟平均访花数为8.44±0.44,极显著高于意大利蜜蜂每分钟的平均访花数2.38±0.15;明亮熊蜂访花间隔为3.81±0.42 s,极显著短于意大利蜜蜂的6.0±0.48 s。明亮熊蜂访花具有选择性,每天访早期花平均为55%,意大利蜜蜂则无选择性,每天访早期花平均为34%,二者差异显著;在9:00～12:00明亮熊蜂访早期花平均为75%,意大利蜜蜂访早期花则仅为31%。熊蜂在花间和花簇间活动频繁,平均移动距离为5.2 m;而意大利蜜蜂很少在花簇间移动,平均移动距离只有1.1 m。据此得出明亮熊蜂为日光温室草莓授粉的活动特性优越于意大利蜜蜂,从而产生更高的授粉效益。     

Behavioral responses by bumble bees to variation in pollen availability

Summary Pollen-collecting bumble bees (Bombus spp.) detect differences between individual flowers in pollen availability and alter their behavior to capitalize on rewarding flowers. Specific responses by bees to increased pollen availability included: longer visits to flowers; visits to more flowers within an inflorescence, including an increased frequency of revisits; an increased likelihood of grooming while the bee flow between flowers within the inflorescence; and more protracted inter-flower flights, probably because of longer grooming bouts. The particular suite of responses that a bee adopted depended on the pollen-dispensing mechanism of the plant species involved. Bees buzzed previously-unvisited Dode-catheon flowers longer than empty flowers. In contrast, pollen availability did not significantly affect the duration of visits to Lupinus flowers, which control the amount of pollen that can be removed during a single visit. Simulation results indicate that the observed movement patterns of bumble bees on Lupinus inflorescences would return the most pollen per unit of expended energy. The increased foraging efficiency resulting from facultative responses by bees to variation in pollen availability, especially changes in the frequency and intensity of grooming, could correspondingly decrease pollen dispersal between plants.     

Annual flower strips support pollinators and potentially enhance red clover seed yield

Ecological intensification provides opportunity to increase agricultural productivity while minimizing negative environmental impacts, by supporting ecosystem services such as crop pollination and biological pest control. For this we need to develop targeted management solutions that provide critical resources to service‐providing organisms at the right time and place. We tested whether annual strips of early flowering phacelia Phacelia tanacetifolia support pollinators and natural enemies of seed weevils Protapion spp., by attracting and offering nectar and pollen before the crop flowers. This was expected to increase yield of red clover Trifolium pratense seed. We monitored insect pollinators, pests, natural enemies and seed yields in a total of 50 clover fields along a landscape heterogeneity gradient, over 2 years and across two regions in southern Sweden. About half of the fields were sown with flower strips of 125–2,000 m². The clover fields were pollinated by 60% bumble bees Bombus spp. and 40% honey bees Apis mellifera. The clover seed yield was negatively associated with weevil density, but was unrelated to bee species richness and density. Flower strips enhanced bumble bees species richness in the clover fields, with the strongest influence in heterogeneous landscapes. There were few detectable differences between crop fields with and without flower strips. However, long‐tongued bumble bees were redistributed toward field interiors and during phacelia bloom honey bees toward field edges. Clover seed yield also increased with increasing size of the flower strip. We conclude that annual flower strips of early flower resources can support bumble bee species richness and, if sufficiently large, possibly also increase crop yields. However, clover seed yield was mainly limited by weevil infestation, which was not influenced by the annual flower strips. A future goal should be to design targeted measures for pest control.     

Comparative nectar-foraging behaviors and efficiencies of an alien and a native bumble bee

Resource preemption by alien organisms can contribute to their invasion success and the demise of functionally equivalent native species, particularly when opportunistic foraging by aliens results in more efficient exploitation. In forests of NW Patagonia, the only native bumble bee and major pollinator, Bombus dahlbomii, declined almost to extinction as the alien B. ruderatus increased in abundance since its first appearance about 17 years ago. To explore whether resource competition might have driven this displacement we studied the behavior and foraging efficiency of both bumble bees while they harvested nectar from flowers of Alstroemeria aurea, the main summer food resource in the forests of NW Patagonia. We compared the nectar content of flowers that bees selected, recently visited, and rejected with that of randomly-chosen neighboring flowers and assessed differences in visitation rates. The native bumble bee selects flowers with abundant nectar and mostly exploits nectar-rich flower patches by rejecting a higher proportion of flowers with little or no nectar. On the other hand, the alien bumble bee discriminated less with respect to sugar content per visited flower, but visited more flowers per minute. Workers of the native bumble bee harvested ~70% more sugar per unit of time than those of the alien species in absolute terms, and a similar amount when sugar harvested was expressed as a percentage of body mass. In contrast to expectation, the opportunistic foraging of the alien bumblebee was not more efficient and therefore cannot explain the ecological extinction of the native species through exploitative competition. These findings suggest that the displacement of the native species by the alien may be driven by other factors, such as the associated introduction of novel diseases or parasites.     

Does the Flower Constancy of Bumble Bees Reflect Foraging Economics?

We examined the effects of floral reward level and spatial arrangement on the propensity of bumble bees to exhibit flower constancy. In three separate experiments, we compared the flower constancy of bees on dimorphic arrays of blue and yellow flowers that differed either in reward concentration, reward volume, or inter‐flower distance. Overall, flower choice patterns varied among bees, ranging from random selection to complete constancy. When flowers contained greater reward volumes and were spaced farther apart, bees showed less flower constancy and more moves to closely neighbouring flowers. Changes in reward concentration had no effect on flower constancy; however, more dilute rewards produced shorter flight times between flowers. In addition, there was a strong positive relationship between degree of flower constancy and net rate of energy gain when flowers were spaced farther apart, indicating that constant bees were more economic foragers than inconstant bees. Together, these results support the view that the flower constancy of pollinators reflects an economic foraging decision.     

Bumble bee abundance and richness improves honey bee pollination behaviour in sweet cherry

Pollination service in agricultural crops increases significantly with pollinator diversity and wild pollinator abundance. Differences in the foraging behaviour of pollinating insects are one of the reasons why pollinator diversity and abundance enhances crop pollination. Here, we focused on the foraging behaviour of honey bees and bumble bees in sweet cherry orchards. In addition, we studied the influence of bee diversity and abundance on the foraging behaviour of honey bees and bumble bees. Honey bees were found to visit fewer flowers than bumble bees. Bumble bees also showed a higher probability of changing trees between rows than honey bees. Both visitation rate and probability of row changes of honey bees increased with bumble bee diversity and with bumble bee abundance. We also found that the probability of row changes of honey bees increased with increasing bumble bee abundance. These effects of bumble bee richness and abundance on the pollination behaviour of honey bees can improve the pollination performance of honey bees in crops that depend on cross pollination. Our results highlight the higher pollination performance of bumble bees and the facilitative effect of wild pollinators to crop pollination.     

BUMBLE BEE POLLINATION AND FLORAL MORPHOLOGY: FACTORS INFLUENCING POLLEN DISPERSAL IN THE ALPINE SKY PILOT,POLEMONIUM VISCOSUM (POLEMONIACEAE)

Pollen dispersal success in entomophilous plants is influenced by the amount of pollen produced per flower, the fraction of pollen that is exported to other flowers during a pollinator visit, visitation frequency, and the complementarity between pollen donor and recipients. For bumble bee-pollinated Polemonium viscosum the first three determinants of male function are correlated with morphometric floral traits. Pollen production is positively related to corolla and style length, whereas pollen removal per visit by bumble bee pollinators is a positive function of corolla flare. Larger-flowered plants receive more bumble bee visits than small-flowered individuals. We found no evidence of tradeoffs between pollen export efficiency and per visit accumulation of outcross pollen; each was influenced by unique aspects of flower morphology. Individual queen bumble bees of the principal pollinator species, Bombus kirbyellus, were similar in male, female, and absolute measures of pollination effectiveness. An estimated 2.9% of the pollen that bumble bees removed from flowers during a foraging bout was, on average, deposited on stigmas of compatible recipients. Significant plant-to-plant differences in pollen production, pollen export per visit, and outcross pollen receipt were found for co-occurring individuals of P. viscosum indicating that variation in these fitness related traits can be seen by pollinator-mediated selection.     

Prey capture by the crab spider Misumena calycina (Araneae: Thomisidae)

Summary Crab spiders Misumena calycina (L.) in pasture rose Rosa carolina flowers regularly attacked bumble bees, smaller bees, and syrphid flies that visited these flowers. Attacks reached a maximum rate of over 20/h during mid morning, but only 1.6% of the most important prey item, bumble bees, were captured. The next most important food source, the most frequently taken item, syrphid flies Toxomerus marginatus (Say), were captured in 39% of the attempts. Since these flies have a biomass only 1/60th that of bumble bees, they comprised a much less important food source than did bumble bees. Spiders would obtain over 7% more food by specializing on bumble bees than by attacking all insect visitors, and as much as 20% more food at certain times of the day. However, they did not show a tendency to specialize at any time.