Local bumble bee decline linked to recovery of honey bees,drought effects on floral resources

Time series of abundances are critical for understanding how abiotic factors and species interactions affect population dynamics, but are rarely linked with experiments and also scarce for bee pollinators. This gap is important given concerns about declines in some bee species. I monitored honey bee (Apis mellifera) and bumble bee (Bombus spp.) foragers in coastal California from 1999, when feral A. mellifera populations were low due to Varroa destructor, until 2014. Apis mellifera increased substantially, except between 2006 and 2011, coinciding with declines in managed populations. Increases in A. mellifera strongly correlated with declines in Bombus and reduced diet overlap between them, suggesting resource competition consistent with past experimental results. Lower Bombus numbers also correlated with diminished floral resources. Declines in floral abundances were associated with drought and reduced spring rainfall. These results illustrate how competition with an introduced species may interact with climate to drive local decline of native pollinators.     

Sublethal neonicotinoid insecticide exposure reduces solitary bee reproductive success

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MECHANISM OF SELECTION FAVORING A WIDE TUBULAR COROLLA IN CAMPANULA PUNCTATA

A previous study of Campanula punctata pollinated by Bombus diversus showed greater male reproductive success in plants with wider corollas when male reproductive success was measured by paternity analysis. Pollen removal alone was not a good measure of male reproductive success. The aim of the current study is to elucidate the mechanism underlying the selection on corolla width in C. punctata. Multiple regression analysis of male reproductive success in experimental populations revealed that the advantage of a wide corolla to the male is independent of the corolla width of pollen recipients, indicating that the position of pollen deposited on Bombus may not be an important factor for selection. However, the number of pollen grains that fell on the petal or off the flower and were lost at the first visit of Bombus (pollen fall) decreased with increasing corolla width, so that most pollen grains removed from a wide flower were deposited onto the pollinator. In a narrow flower, a greater proportion of the pollen removed was wasted through pollen fall. Pollen removal does not reflect male reproductive success, at least in part because of the loss of pollen in some flowers through pollen fall. The positive relationship between wider corollas and reduced loss of pollen through pollen fall is likely to lead to greater male reproductive success of wider flowers under repeated visits of pollinators. Decreased pollen fall, probably due to more gentle contact between pollen and bees in flowers with wider corollas, may be one of the mechanisms underlying the selection on corolla width of C. punctata.     

Pollinator directionality as a response to nectar gradient: promoting outcrossing while avoiding geitonogamy

Plants with multiple flowers could be prone to autonomous self‐pollination and insect‐mediated geitonogamy, but physiological and ecological features have evolved preventing costs related to autogamy. We studied the rare perennial herb Dictamnus albus as a model plant, with the aim of describing the plant–pollinator system from both plant and pollinator perspectives and analysing features that promote outcrossing in an entomophilous species. The breeding system and reproductive success of D. albus were investigated in experimental and natural conditions, showing that it is potentially self‐compatible, but only intra‐inflorescence insect‐mediated selfing is possible. Nectar analysis showed gender‐biased production towards the female phase, which follows the male phase, and during flowering, full blooming is found in flowers at the bottom of the raceme. Among a wide spectrum of insect visitors, three genera (Bombus, Apis, Megachile) were found to be principal pollinators. A study of insect behaviour showed a tendency towards bottom‐to‐top flights for the most important pollinators Bombus spp. and Apis mellifera: upward movements on the racemes could be explained by foraging behaviour, from more to less rewarding flowers. In accordance with the ‘declining reward hypothesis’, bumblebees and honeybees leave the plant when gain of reward is low, after which few flowers are visited, reducing the chance of self‐pollen transfer among flowers. Intra‐flower self‐pollination is prevented in D. albus by protandry and herkogamy, while the nectar‐induced sequential pattern of pollinator visits avoids geitonogamy and tends to maximise pollen export, promoting outcrossing. All these features for preventing selfing benefit plant fitness and population genetic structure.     

The superiority of bumblebees to honeybees as pollinators: insect visits to raspberry flowers

Abstract.

• 1 The behaviour and activity patterns of Apis mellifera and of five species of Bombus were analysed in relation to climatic variables and nectar quality on three varieties of unsprayed cultivated raspberry (Rubus idaeus) in eastern Scotland.
• 2 Stages of floral morphology and reward were similar for the three varieties: young flowers offered both nectar and pollen, but medium and old flowers offered nectar only, in diminishing quantities.
• 3 A wide range of insects visited raspberry flowers, but bees were dominant, bumblebees being responsible for about 60% of all visits and honeybees making up most of the remaining percentage. All bees had substantial pollen deposited on their bodies during visits, though few specifically collected it.
• 4 Bombus spp. were found to favour young (receptive) flowers strongly, especially early in the morning when pollen was most abundant: whilst Apis visited unselectively. Bumblebees also foraged over substantially longer periods of the day, and in poorer weather, some being present at most times of observation; and they foraged more quickly in terms of flower visits per minute.
• 5 Bombus carried more pollen on their bodies than Apis, and also deposited more pollen on raspberry stigmas, with B.lapidarius and B.terrestris being particularly effective and also being the most abundant species. All bumblebees also foraged over a longer range, moving between canes and rows more frequently than did honeybees.
• 6 Bumblebees are therefore likely to be substantially more important as pollinators of raspberries than are honeybees, especially as raspberries though moderately self-fertile may exhibit metaxenia. Reasons why Bombus may be the preferred pollinator in most sites of raspberry cultivation are discussed, together with implications for present and future growers.

     

Correlates of reproductive success among field colonies of Bombus lucorum: the importance of growth and parasites

Abstract.

• 1 In natural populations, colonies of bumble bees vary in many important life history traits, such as colony size and age at maturity, or the number and sex of reproductives produced. We investigated how the presence of parasites in field populations of the bumble bee Bombus lucorum L. relates to variation in life history traits and reproductive performance. A total of thirty-six colonies was placed in accessible nest sites in the field and monitored at regular intervals throughout a season.
• 2 Among the life history correlates, early nest foundation was strongly associated with large maximum colony size, old age and large size at maturity, and this in turn with successful production of males and queens, as well as with the number of sexuals produced. Overall, reproductive success was highly skewed with only five colonies producing all the queens. Sixteen colonies failed to reproduce altogether.
• 3 The social parasite Psithyrus was abundant early in the Bombus colony cycle and preferentially invaded host nests with many first brood workers and thus disproportionately large size, i.e. those colonies that would otherwise be more likely to reproduce or produce (daughter) queens rather than males. To prevent nest loss, Psithyrus had to be removed soon after invasion. Therefore, the effects reported here can only be crude estimates.
• 4 Parasitoid conopid flies are likely to cause heavy worker mortality when sexuals are reared by the colonies. Their inferred effect was a reduction in biomass that could be invested in sexuals as well as a shift in the sex ratio at the population level resulting from failure to produce queens. We suggest to group the inferred correlates into ‘early events’ surrounding colony initiation and social parasitism, and ‘late events’ surrounding attained colony size in summer and parasitism by conopid flies. Our evidence thus provides a heuristic approach to understand the factors that affect reproductive success of Bombus colonies.

     

Electrophoretical studies of proteins of the hypopharyngeal glands and of the larval food ofMelipona quadrifasciata anthidioides Lep. (Hymenoptera,Meliponinae)

Summary The electrophoretical protein patterns of hypopharyngeal glands, larval food ofMelipona, and royal jelly ofApis were compared.Since protein patterns of hypopharyngeal glands from newly emerged workers, brood cell provisioners and foragers are similar to freshly deposited larval food, the identical protein bands probably represent actual gland secretion. This suggests that, as inApis, the glands secrete proteins to the larval food, and maintain this ability throughout life, although at slightly different intensities, according to the activity of the bees.The similarity on the electrophoretic profiles of the major larval food protein inApis andMelipona is an interesting finding because of its probable evolutionary significance.     

POLLEN-FORAGING BEHAVIOR OF BOMBUS IN RELATION TO POLLINATION OF NOTOTRIBIC FLOWERS

Cinematographic records of the pollen-foraging behavior of six Bombus species on Linaria vulgaris, Lobelia siphilitica, and Antirrhinum majus revealed a generally uniform pattern of pollen deposition by the nototribic flowers on the frons and scutum of the foragers. A forward sweeping motion of the tarsal brushes of their middle legs removed some of this pollen which was transferred to the tibial corbicula of the hind legs. Some insects foraged in an inverted position. An analysis of 804 pollen samples from frons, scutum, and corbiculum of 331 from a total of 395 Bombus visitors, representing eight of the nine native species, on the three plants indicated a high proportion of proper pollen being collected in addition to 15 kinds of foreign pollen. The pollen-sweeping behavior of Bombus on nototribic flowers is suggested as an important means of pollen-foraging apart from its utility in insect grooming. Pollen-foraging insects are considered important pollinators of these nototribic flowers.     

Comparative analysis of volatile components from labial glands of male Japanese bumblebees (Bombus spp.)

The volatile components from the labial glands of males of six Japanese bumblebee species were analyzed and compared. Clear species‐specificity was found. Ethyl dodecanoate was identified as the major component from the glands of Bombus (Bombus) hypocrita hypocrita and Bombus (Bombus) hypocrita sapporoensis while dihydrofarnesal and dihydrofarnesol were the major components from Bombus (Bombus) ignitus. Citronellol and trans,trans‐farnesol were found from Bombus (Pyrobombus) ardens ardens and Bombus (Diversobombus) diversus diversus, respectively. trans,trans‐Farnesol was also found from Bombus (Diversobombus) diversus tersatus in Hokkaido. Such differences strongly suggest that these chemicals play an important role in reproductive isolation between sympatric species of Japanese bumblebees.     

Testing population-level mechanisms of invasion by a mobile vertebrate: a simple conceptual framework for salmonids in streams

Invasion biology suffers from a lack of the ability to predict the outcome of particular invasions because of reliance on verbal models and lack of rigorous experimental data at the appropriate scale. More progress is likely to be made by considering invasions as population-level phenomena and initially focusing on specific taxa or particular categories of invasions. To this end, we propose a simple conceptual framework to motivate studies of invasion by salmonids (salmon, trout, grayling, and whitefish) in streams that emphasizes population-level mechanisms affecting native species and promoting spread by the invader. Specifically, the only direct mechanisms by which the abundance of the native species can decline are through biotic interactions which cause decreased reproductive rates or survival at specific life stages, net emigration, debilitating or fatal diseases introduced by the invader, or a combination of these factors. Conversely, abundance of the invader must increase by local reproduction, high survival, net immigration, or a combination of these factors. Review of existing salmonid invasion literature suggests that future studies could be improved by using manipulative field experiments at a spatial and temporal scale appropriate to address population-level processes, characterizing how movement affects the establishment and spread of an invader, and including abiotic context in experimental designs. Using the example of brook trout (Salvelinus fontinalis) invasion into streams containing native Colorado River cutthroat trout (Oncorhynchus clarki pleuriticus) in the central Rocky Mountains (USA), we demonstrate how the framework can be used to design a manipulative field experiment to test for population-level mechanisms causing ecological effects and promoting invasion success. Experiments of this type will give invasion ecologists a useful example of how a taxon-specific invasion framework can improve the ability to predict ecological effects, and provide fishery biologists with the quantitative foundation necessary to better manage stream salmonid invasions.     

BUMBLEBEE POLLINATION RELATIONSHIPS ON THE BEARTOOTH PLATEAU TUNDRA OF SOUTHERN MONTANA

The coadaptive, dynamic relationship between the members of a floral community and their respective bumblebee pollinators was studied on the alpine-tundra of the Beartooth Plateau in southern Montana. A total of ten species of Bombus was observed foraging for pollen and/or nectar on Castilleja pulchella, Delphinium bicolor, Lupinus monticola, Mertensia ciliata, Oxytropis campestris, Penstemon procerus, and Trifolium dasyphyllum. The number of Bombus species per plant species ranged from 1 to 9. Based on relative percentage of pollen types in corbicular loads, monolectic foragers comprised 53.5% and polylectic foragers 46.5% of the bumblebees. Examinations of relative length of nectariferous corolla-tubes, tongue-length of pollinators, foraging frequency of pollinators, phenology of floral anthesis, and stature of plants did not indicate specific resource partitioning. Non-tundra-nesting bumblebees from lower elevations preferred adventive or typically non-tundra plants. Examination of perianth colors in visible light by reflectance spectrophotometry and in long-wave (360 nm) ultraviolet light by photography disclosed well-defined visible light reflectance spectra in all species but ultraviolet reflectance patterns only in D. bicolor. Insect collections and exclosure studies indicated all plant species except D. bicolor and P. procerus are highly reliant on bumblebee pollinators.     

The impact of sulfur on the reproductive success of <Emphasis Type="Italic">Anagrus</Emphasis> spp. parasitoids in the field

Pesticides targeted at pest species have often been demonstrated to have strong adverse effects on the survival of biological control agents in short-term laboratory bioassays; however, studies examining the influence of pesticides on the actual reproductive success of biological control agents in the field are rare. Because natural enemy reproduction is often directly tied to biological control success, effects of pesticides on reproduction are of central importance. Here we use a new technique to examine the influence of sulfur, a fungicide widely used in grape production, on the reproductive success of Anagrus erythroneurae (Hymenoptera: Mymaridae) and Anagrus daanei (Hymenoptera: Mymaridae), egg parasitoids of the grape leafhopper, Erythroneura elegantula (Homoptera: Cicadellidae). Sulfur has previously been shown to be highly toxic to Anagrus spp. in short-term laboratory and field bioassays, creating the expectation that sulfur should also reduce Anagrus reproductive success in the field. Surprisingly, in two studies, the first comparing the oviposition success of Anagrus collected live in paired sulfur-treated versus untreated vineyards and the second comparing the lifetime reproductive success of Anagrus collected at the end of their lives in unpaired sulfur-treated versus untreated vineyards, we found no effect of sulfur on parasitoid reproductive success. In this system, traditional short-term assays of laboratory toxicity do not appear to predict effects on parasitoid reproductive success, suggesting that demographic approaches to assessing the disruptive effects of pesticides may have an important role in designing IPM programs.     

Monitoring bee populations: are eusocial bees attracted to different colours of pan trap than other bees?

Declines in pollinator populations have made monitoring pollinators, in particular bees, increasingly important. There is general agreement among practitioners that using a mix of trap colours is important, but the empirical evidence to support this is scattered. During studies of bees in forestry cutovers, large differences were noted in capture rate among white, blue, and yellow pan traps. Pooled data from collections in cutovers and commercial cranberry fields demonstrated significant differences in the effect of trap colour, with the largest numbers captured in white traps, and the fewest in yellow, but only for the genus Bombus Latreille (Hymenoptera: Apidae). The colour preference was consistent with the spectral sensitivity of Bombus, and the visible reflectance spectra of the traps. A literature review suggested that among eusocial bees, Apis Linnaeus (Hymenoptera: Apidae) are more attracted to white traps and Bombus are more attracted to blue traps, while non-eusocial bees with a variety of social structures are more attracted to yellow. Among the non-eusocial bees, Halictidae were somewhat attracted to blue, while Andrenidae were not. This supports the common practice of using white, blue, and yellow traps when surveying bees to ensure adequate taxonomic representation.     

Chronology of reproductive investment determines predation risk aversion in a felid‐ungulate system

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Reproductive biology and pollination of Utricularia reniformis A.St.‐Hil. (Lentibulariaceae)

Utricularia reniformis is an endemic Brazilian carnivorous plant, most common in high‐altitude grasslands. Knowledge of the reproductive biology of U. reniformis is essential for planning conservation strategies, but it is currently poorly understood. Thus, we studied the floral morphology, floral biology, breeding system and pollination of this species. U. reniformis produces and stores nectar in the flower spur, a classic feature of bee‐pollinated flowers, and we recorded Xylocopa sp. and Bombus sp. as pollinators. Moreover, although it is self‐compatible it is an obligate animal‐pollinated species, as the sensitive stigma avoids self‐pollination. However, in natural conditions reproductive success is low due to the rarity of visits from pollinators. We suggest that the low reproductive success caused by a deficit of pollinators may affect gene flow, causing loss of genetic diversity in U. reniformis.     

POLLINATION ADAPTATION IN PEDICULARIS GROENLANDICA

Cinematographic and stereophotographic records indicate that Pedicularis groenlandica is pollinated in the Colorado Front Range by seven species of pollen-foraging bumblebees (Bombus sp.) to which the nectarless flower is intricately adapted functionally and structurally. Removing pollen by wing vibrations of an oscilloscopically identified frequency significantly distinct from flight vibration frequency, foragers carried pollen loads with up to three foreign pollen types in addition to Pedicularis pollen, which was found in all loads. No direct correlation was evident between flight vibration frequency and combined body-pollen load weight, ambient air temperature, or forager species. The flower is phenologically and morphologically adapted to the worker caste of apparently any Bombus species available to it throughout the plant's montane-alpine zone vertical-distribution range. The evolutionary position of the pollination mechanism is considered in relation to the floral morphology of other species in the genus Pedicularis.     

The influence of an invasive plant species on the pollination success and reproductive output of three riparian plant species

Besides competition for abiotic resources, an increasing number of studies show evidence of the effects of invasive species on the pollination success and reproductive output of indigenous species. We studied the effect of the invasive Impatiens glandulifera Royle on the process of reproduction in the indigenous Lythrum salicaria L. and Alisma plantago-aquatica L. and the naturalized Oenothera biennis L. The latter three species (target species) were transplanted into pots and placed in invaded and non-invaded areas. During flowering season of each of these species, we measured species composition and abundance of pollinators, pollinator behaviour, pollen deposition and female reproductive output of the target species. Competitive effects were found for L. salicaria, in which fewer pollinator species and number of foraging individuals were observed, and also, lower pollen deposition and seed set were measured in these invaded populations. In contrast, the reproductive success of A. plantago-aquatica and O. biennis was not affected by the presence of I. glandulifera. Our data indicate that when invasive and indigenous species show a large overlap in pollinator community, which is the case for I. glandulifera and L. salicaria, competition between these species can occur. When both species have a different pollinator community, pollination success and reproductive output is not affected, even when the indigenous populations are densely and abundantly invaded.     

Effects of Local Plant Density and Incomplete Dichogamy on the Reproductive Success of the Rare Neotropical Palm Geonoma epetiolata

Density dependent processes are known to influence reproduction and establishment of plant populations. In this study, we evaluated the effects of local density and sexual expression on the reproductive success of the rare palm species Geonoma epetiolata in Costa Rica. We classified individuals in two density categories based on distances to the two nearest neighbors and recorded the occurrence of sexual overlap on each individual. Overlap between pistillate and staminate flowers in monoecious plants allows geitonogamous pollination, potentially reducing dependence on mates for reproduction. We measured plant size and light availability, and evaluated the influence of these variables on pollination success, fruit production, fruit abortion and seed mass. Pollination success significantly increased with density but there was no effect of sexual overlap. In contrast, there was no effect of density on the probability of initiated fruit, and a negative effect on fruit set. Fruit abortion was lowest in isolated plants with no sexual overlap. Plant size and light did not contribute to variation in reproductive success. In conclusion, the pollination advantage of plants in dense neighborhoods does not compensate reproductive losses incurred by fruit abortion, possibly due to mating among genetically related individuals. Geonoma epetiolata is threatened by habitat loss and poaching of seeds for the horticultural market. High fruit abortion rates associated with density in G. epetiolata suggest that seed collections from the remnant wild populations of this palm species may cause bottlenecks that further threaten population viability.     

Experimental effect of consumer identity on the invasion success of a non-native cladoceran

An important goal of ecologists is to identify the characteristics of native communities that help to either promote or resist the invasion of non-native taxa. In this study, experimental mesocosms were used to determine how the richness and species identity of freshwater consumers influenced the invasion success of Daphnia lumholtzi (DL), a cladoceran that has successfully invaded aquatic habitats throughout the United States. Three species of native zooplankton were used to create a gradient of richness in replicated mesocosms that included all species in monoculture, all two species combinations, and all three species together. DL was then added to each mesocosm and its biomass was monitored over time. While additional research is needed to better determine how richness affects the invasion success of DL, the presence of native zooplankton resulted in reduced levels of DL biomass in all treatments relative to the zooplankton free controls. One species (Daphnia magna, DM) was able to reduce the biomass of DL to lower levels than the other two species. DL also appeared to be unable to establish or persist over time in mesocosms with DM, unlike in mesocosms with the two other species. These species–specific effects on invasion success appeared to be related to DM’s ability to reduce algal biomass to lower levels than the other two species. Therefore, while the presence of native zooplankton helps to reduce the biomass of DL once it is introduced into novel systems, the degree to which DL is able to establish and maintain populations over time within individual systems will likely depend on the presence or absence of particular species that can have particularly strong impacts on invasibility. Using such data, we may be able to predict which habitats are most likely to be invaded based on the presence or absence of individual native species.     

Plant–pollinator interactions between an invasive and native plant vary between sites with different flowering phenology

Floral displays of invasive plants have positive and negative impacts on native plant pollination. Invasive plants may also decrease irradiance, which can lead to reduced pollination of native plants. The effects of shade and flowers of invasive plant species on native plant pollination will depend on overlap in flowering phenologies. We examined the effect of the invasive shrub Lonicera maackii on female reproductive success of the native herb Hydrophyllum macrophyllum at two sites: one with asynchronous flowering phenologies (slight overlap) and one with synchronous (complete overlap). At each site, we measured light availability, pollinator visitation, pollen deposition, and seed set of potted H. macrophyllum in the presence and absence of L. maackii. At both sites, understory light levels were lower in plots containing L. maackii. At the asynchronous site, H. macrophyllum received fewer pollinator visits in the presence of L. maackii, suggesting shade from L. maackii reduced visitation to H. macrophyllum. Despite reduced visitation, H. macrophyllum seed set did not differ between treatments. At the synchronous site, H. macrophyllum received more pollinator visits and produced more seeds per flower in the presence of co-flowering L. maackii compared to plots in which L. maackii was absent, and conspecific pollen deposition was positively associated with seed set. Our results support the hypothesis that co-flowering L. maackii shrubs facilitated pollination of H. macrophyllum, thereby mitigating the negative impacts of shade, leading to increased seed production. Phenological overlap appears to influence pollinator-mediated interactions between invasive and native plants and may alter the direction of impact of L. maackii on native plant pollination.