Variation in Nectar and Pollen Availability,Sucrose Preference,and Daily Response in the Use of Flowers by <Emphasis Type="Italic">Heliconius erato phyllis</Emphasis>

The mechanisms mediating the use of flowers in the butterfly Heliconius erato phyllis (Nymphalidae) are poorly understood. Availability of nectar and pollen, nectar concentration, and abundance of Stachytarpheta cayennensis and Lantana camara (Verbenaceae), two flower species commonly used by H. erato phyllis in the Neotropics, as well as flower use by this butterfly species in the field were examined in southern Brazil. Under insectary conditions, the preference of H. erato phyllis for different sucrose concentrations (0, 10, 20, 40, and 80%) and the ability to associate sucrose concentrations with preferred and non-preferred flower colors were evaluated through choice tests. Lantana camara inflorescences were less abundant, but contained larger amounts of pollen and nectar than S. cayennensis, and H. erato phyllis utilized the flowers of the former species with higher frequency compared to the latter. In the choice tests, butterflies fed more intensely on 20 and 40% sucrose solutions, an interval in which the nectars of L. camara and S. cayennensis are situated, and were able to associate preferred sucrose concentrations with flower color efficiently within the color spectrum of L. camara flowers (i.e., preferred colors), but not within that of S. cayennensis (non-preferred colors). Thus, the greater use of L. camara flowers by H. erato phyllis is related to the plant’s superior floral rewards and not flower abundance, and to the cognitive abilities of these butterflies to adjust their feeding to the availability of pollen and nectar. To our knowledge, this is the first report showing sucrose preferences in a butterfly species.     

A Matter of Contrast: Yellow Flower Colour Constrains Style Length in Crocus species

Most flowers display distinct colour patterns comprising two different areas. The peripheral large-area component of floral colour patterns attracts flower visitors from some distance and the central small-area component guides flower visitors towards landing sites. Whereas the peripheral colour is largely variable among species, the central colour, produced mostly by anthers and pollen or pollen mimicking floral guides, is predominantly yellow and UV-absorbing. This holds also for yellow flowers that regularly display a UV bull’s eye pattern. Here we show that yellow-flowering Crocus species are a noticeable exception, since yellow-flowering Crocus species–being entirely UV-absorbing–exhibit low colour contrast between yellow reproductive organs and yellow tepals. The elongated yellow or orange-yellow style of Crocus flowers is a stamen-mimicking structure promoting cross-pollination by facilitating flower visitors’ contact with the apical stigma before the flower visitors are touching the anthers. Since Crocus species possess either yellow, violet or white tepals, the colour contrast between the stamen-mimicking style and the tepals varies among species. In this study comprising 106 Crocus species, it was tested whether the style length of Crocus flowers is dependent on the corolla colour. The results show that members of the genus Crocus with yellow tepals have evolved independently up to twelve times in the genus Crocus and that yellow-flowering Crocus species possess shorter styles as compared to violet- and white-flowering ones. The manipulation of flower visitors by anther-mimicking elongated styles in Crocus flowers is discussed.     

The significance of flower colour change in eight co-occurring shrub species

Flower colour changes from white or yellow to various shades of red at or near the sites of harvestable pollen in Calytrix glutinosa, Grevillea pilulifera, Isopogon dubius and Petrophile biloba , and over most of the flower in Hypocalymma angustifolium, Verticordia chrysantha and V. huegelii and over the pseudanthium in Darwinia citriodora. All bee, wasp, beetle, fly, butterfly and moth visitors select flowers in the white/yellow phase rather than the red or intermediate phase.
Nectar is produced by five species, harvestable pollen by four species and detectable perfume by three species, all of which features are usually absent from the red phase. The timing of the colour change in all species also corresponds to loss of stigma receptivity, completion of pollination and onset of ovule seed) swelling. Six species also undergo minor morphometric changes which discourage visitation. In all species, colour change is non-inducible by pollinators, taking 2–30 days to complete. In three protandrous species, all available pollen may be removed in the first visit, requiring transport of non-self pollen to rewardless flowers during the 10 h period of the yellow phase.
These species are highly floriferous and occur in dense patches. Since only a small proportion of flowers may be receptive at any one time, it is concluded that retention of flower parts essentially serves to enhance long-distance attraction, while colour change maximizes pollination and foraging efficiency.     

Floral colour change in Pedicularis monbeigiana (Orobanchaceae)

We examined the effects of the retention of colour-changed flowers on long- and short-distance attractiveness of bumblebees and the likelihood of successive flower visits by bumblebees in Pedicularis monbeigiana. The lower lip changed colour with age from white to purple. Hand geitonogamous pollination significantly reduced seed production. No pollen limitation occurred in this species. Purple-phase flowers contributed minimally to pollinator attractiveness at long distance. The combination of less reproductive flowers with a lower amount of reward and floral colour change enabled plants to direct pollinators to reproductive, highly rewarding white flowers at close range. A high percentage of purple-phase flowers in an inflorescence was associated with a marked reduction in the frequency of successive flower visits to individual plants. We suggest floral colour change in P. monbeigiana may serve as a mechanism for enhancing inter-individual pollen transfer and reducing intra-individual pollen transfer.     

One for all and all for one: retention of colour‐unchanged old flowers increases pollinator attraction in a hermaphroditic plant

• Long‐lived flowers increase pollen transfer rates, but these entail high water and carbon maintenance costs. The retention of pollinated and reward‐free old flowers enhances pollinator visitation to young receptive flowers by increasing floral display size. This mechanism is associated with acropetal inflorescences or changes in flower colour and openness, but the retention of unchanging solitary flowers remains overlooked.
• We examined pollination‐dependent variation in floral longevity and determined stigmatic receptivity, pollen viability and pollen removal rates among flower ages in Kielmeyera regalis, a Neotropical savanna shrub. We also evaluated the effects of floral display size on pollinator visitation rates. Lastly, we determined whether old flowers are unvisited and exclusively increase pollinator attraction to young flowers through flower removal experiments.
• Regardless of pollination treatment, flowers lasted fully open with no detectable physical changes for 3 days. Over time, stigmas remained receptive but >95% of pollen was removed. Pollinator visitation significantly increased with floral display size and intermediate percentages (15–30%) of newly opened flowers. Accordingly, the retention of reward‐free and unvisited old flowers increased young flower–pollinator interaction.
• Our results reveal the importance of a prolonged floral longevity in increasing pollinator attraction toward newly opened receptive flowers without changes in flower colour and form. We conclude that the retention of pollinated, reward‐free and unvisited colour‐unchanged old flowers in K. regalis is a strategy that counteracts the water use costs associated with the maintenance of large flowers with increased mate opportunities in a pollen‐limited scenario.

     

In a world of white,flower colour matters: A white–purple transition signals lack of reward in an alpine Euphrasia

The New Zealand alpine flora displays a range of unusual characteristics compared with other alpine floras, in particular the high frequency of species with small white flowers. The presence of both white and bright purple flowers on the same plant in the New Zealand alpine annual creeping eyebright (Euphrasia dyeri Wettst.) provides an ideal opportunity to investigate the significance of flower colour in an environment where coloured flowers are rare. The relationships among flower age, gender phase, reward availability and petal colour were assessed in natural populations of E. dyeri. The effect of pollination on flower colour was tested using hand pollination of bagged flowers. Direct observations and videos of flowers were used to assess patterns of flower visitation by native and introduced pollinators. Unpollinated white E. dyeri flowers changed from white to purple within 6 days. However, pollination of white flowers triggered a significantly faster colour change, typically within 1–2 days. White flowers had receptive stigmas, large amounts of lipid‐rich pollen and small amounts of nectar, whereas stigmas of purple flowers are not receptive and flowers did not provide pollen or nectar rewards. Flowers were mainly visited by native syrphid flies. Both native syrphids and introduced Bombus bees showed a marked avoidance of purple flowers, tending to preferentially visit white flowers. Our study suggests that flower colour change from white to bright purple in E. dyeri functions to direct pollinators to rewarding, receptive flowers. As many Euphrasia L. species are described as having variably coloured flowers, this mechanism may be more widespread in the genus. Furthermore, our results add to the growing evidence that the dominance of white flowers in the New Zealand alpine is not simply due to a lack of colour discrimination among pollinators.     

Red oilseed rape? The potential for manipulation of petal colour in control strategies for the pollen beetle (Meligethes aeneus)

The pollen beetle (Meligethes aeneus) is a major pest of oilseed rape (Brassica napus) at the inflorescence stage and is well known to prefer colours called yellow by human observers over many other colours. While commercial cultivars of oilseed rape have yellow flowers, little is known about the potential to manipulate host plant location and reduce subsequent infestation by this pest through variation in flower colour. We investigated the responses of pollen beetles to flowers of a white-petalled oilseed rape variety that had been dyed different colours in semi-field arena and field experiments. Flowers dyed blue or red were less heavily infested than those dyed yellow or the white flowers, indicating that blue and red flowers were less attractive than yellow and white ones. This response was most likely due to differences in petal colour because olfactometer studies showed that beetle responses to the odours of the coloured treatments did not differ. The comparatively high infestation of untreated white flowers is interpreted as a consequence of their high UV reflectance; the presence of a UV receptor in M. aeneus is suggested, and its role in visually guided insect–plant interactions in this species described. The potential for manipulation of petal colour in control strategies for the pollen beetle is discussed.     

Flower colour change in Banksia ilicifolia: A signal for pollinators

Both birds and insects visit yellow flower heads of Banksia ilicifolia rather than those in the pink or red phases. Birds carry most pollen. Substantial nectar and pollen rewards are present only in the yellow phase. The timing of flower colour change also corresponds to a decline in viability of presented pollen and stigma receptivity. Colour change is age-dependent rather than pollinator-induced. Bird visits to yellow or red heads are essentially determined by the availability of nectar in each rather than differences in their visibility. Fruit set is negligible in the absence of pollinators but still < 1% in their presence. Banksia ilicifolia has the smallest heads and is the most localized of five co-occurring and partly co-flowering Banksia species. It is hypothesized that the restriction of flower colour change to B. ilicifolia increases the competitiveness of this species: bird visitors are directed to flower heads with abundant nectar, viable pollen and receptive stigmas, foraging and pollination efficiency thereby being enhanced without a marked reduction in long-distance attractiveness of the tree to potential pollinators.     

Role of morphological variables of the visitor butterfly species in relation to their foraging behaviour on Lantana camara: Implication for conservation

The study of foraging behaviour of butterflies has been an important focus among the lepidopterists for years. Although established as invasive weed plant, the role Lantana camara as an important host plant as well as a food plant for the butterfly species is now well-known. The present study aims to interpret the role of morphological variables of the visitor butterflies in relation to their foraging behaviour on Lantana camara. Butterflies with longer proboscis were more efficient in foraging on flowers of Lantana camara than the butterflies with shorter ones, when the species containing proboscis same as or longer than their body length were excluded. Longer relative proboscis length (RPL) have selective advantage for foraging over Lantana camara up to a certain point (RPL = 0.881) and after that larger relative proboscis length often obstructs foraging behaviour as the handling time increases and these butterflies face more resistance against incoming nectar than the others.The residuals (body weight-wing span) also act as important factor.The handling time of the butterflies on Lantana camara shows a negative relationship with the residuals. The findings suggests that in case of Lantana camara as a nectaring plant butterfly species with longer proboscis have selective advantage for exploitation of the resource than the species with shorter ones and plantation of Lantana camara may be useful for conserving the long tongued butterfly species.     

The Effect of Pollination and Ethylene on the Colour Change of the Banner Spot of Lupinus albifrons (Bentham) Flowers

In Lupinus albifrons flowers the banner spot of the standardis initially coloured white or pale yellow. Two to three daysafter reaching the stage of full flower opening, this bannerspot develops a pinkish blush and is deep magenta after a further24 h. The development of this pigmentation is accelerated byexposure to ethylene in a concentration- and time-dependentmanner. Flowers with a pinkish banner spot produced the greatestamounts of ethylene and production was much lower in flowerswhich had either completed the colour change or in which thebanner spot colour remained unchanged. Treatments such as stigmaremoval or pollination increased the rate of ethylene production.Dissection of the flowers showed that while the banner spotis changing colour there is no change in the rate of productionof ethylene from the standard, i.e. from the banner spot orsurrounding tissue. The major sites of production at this timeare the keel and pistil. Isolated flowers withered within 2 d of removal from the plantand therefore did not show any change in the colour of the bannerspot unless exposed to ethylene. The increase in banner spotpigment was about fourfold when isolated floweres were exposedto ethylene (0·24 µl 1^–1): however, the increasewas less than twofold when isolated standards were exposed toethylene (0·27 µl I^–1). Application of silverthiosulphate (STS) to intact isolated flowers, as a 1 h pulseprior to ethylene exposure, partially prevented the pigmentaccumulation, whilst a continuous supply of STS reduced theethylene-induced colour change by approx. 50% Low concentrationsof cycloheximide (CHI) (0·01 mg ml^–1) reduced theaccumulation of pigment in the banner spot of ethylene-treatedflowers, and higher concentrations (1·0 mg ml^–1)completely prevented the ethylene-induced colour change. Ethylene, flower senescence, Lupinus albifrons, pollination     

Responses to olfactory and visual cues by over-wintered and summer generations of the pollen beetle, Meligethes aeneus

Abstract.  Behavioural responses to odours of oilseed rape in bud and flower stage and to green and yellow colours are studied for the two main phenological stages of pollen beetles, Meligethes aeneus , a major pest of oilseed rape, Brassica napus . Over-wintered individuals oviposit in buds of oilseed rape. Adults of the new generation (i.e. the summer generation) feed on flowers of different plant species before over wintering. In olfactometer experiments, the over-wintered beetles display a higher preference for odour of oilseed rape at the bud stage compared with the summer generation, both with and without colour stimuli. Flower odours are preferred in combination with yellow colour. Colour stimuli presented alone do not affect the behaviour. The summer generation beetles respond to both bud and flower odour. Adding colour stimuli changes the summer generations preference towards yellow and flower odour.     

The role of pollinators in maintaining variation in flower colour in the Rocky Mountain columbine,Aquilegia coerulea

Background and Aims Flower colour varies within and among populations of the Rocky Mountain columbine, Aquilegia coerulea, in conjunction with the abundance of its two major pollinators, hawkmoths and bumble-bees. This study seeks to understand whether the choice of flower colour by these major pollinators can help explain the variation in flower colour observed in A. coerulea populations.Methods Dual choice assays and experimental arrays of blue and white flowers were used to determine the preference of hawkmoths and bumble-bees for flower colour. A test was made to determine whether a differential preference for flower colour, with bumble-bees preferring blue and hawkmoths white flowers, could explain the variation in flower colour. Whether a single pollinator could maintain a flower colour polymorphism was examined by testing to see if preference for a flower colour varied between day and dusk for hawkmoths and whether bumble-bees preferred novel or rare flower colour morphs.Key Results Hawkmoths preferred blue flowers under both day and dusk light conditions. Naïve bumble-bees preferred blue flowers but quickly learned to forage randomly on the two colour morphs when similar rewards were presented in the flowers. Bees quickly learned to associate a flower colour with a pollen reward. Prior experience affected the choice of flower colour by bees, but they did not preferentially visit novel flower colours or rare or common colour morphs.Conclusions Differences in flower colour preference between the two major pollinators could not explain the variation in flower colour observed in A. coerulea. The preference of hawkmoths for flower colour did not change between day and dusk, and bumble-bees did not prefer a novel or a rare flower colour morph. The data therefore suggest that factors other than pollinators may be more likely to affect the flower colour variation observed in A. coerulea.     

Colour vision in diurnal and nocturnal hawkmoths

Diurnal and nocturnal hawkmoths (Sphingidae, Lepidoptera) havethree spectral types of receptor sensitive to ultraviolet, blueand green light. As avid flower visitors and pollinators, theyuse olfactory and visual cues to find and recognise flowers.Moths of the diurnal species Macroglossum stellatarum and thenocturnal species Deilephila elpenor, Hyles lineata and Hylesgallii use and learn the colour of flowers. Nocturnal speciescan discriminate flowers at starlight intensities when humansand honeybees are colour-blind. M. stellatarum can use achromatic,intensity-related cues if colour cues are absent, and this isprobably also true for D. elpenor. Both species can recognisecolours even under a changed illumination colour.     

Arabinogalactan-Proteins of the Female Sexual Tissue of Nicotiana alata: I. Changes during Flower Development and Pollination

Arabinogalactan-proteins (AGPs), isolated from the pistils of Nicotiana alata, an ornamental tobacco, are developmentally regulated. Both the total amount and concentration of AGP in the stigma increase during flower development, reaching 10 micrograms AGP/stigma at maturity. In contrast, AGP concentration in the style remains constant throughout the maturation period reaching 12 micrograms AGP/style at maturity. The classes of AGP present in the stigma and style during flower development, separated according to their charge by crossed-electrophoresis, are different and change during development. Pollination of flowers of N. alata with compatible or incompatible pollen results in a significant and reproducible increase in the amount of AGPs in the stigma, but not the style, compared with control unpollinated pistils. Pollination with ethanol vapor inactivated pollen also results in an increase in the amount of AGP in the stigma, but this is less than half that observed following pollination with viable pollen. There are no significant differences in the classes of AGP, based on crossed-electrophoresis, present in the pistil following pollination.     

Attributes of Individual Flowers of Brassica napus L. are Affected by Defoliation but not by Intraspecific Competition

To investigate the effect of intraspecific competition on floweringin Brassica napus‘Westar’, a series of 30 pots wasestablished that spanned a range of one–96 plants perpot. In each pot, the following attributes of individual flowerswere quantified: petal length; petal width; stamen length; pistillength; pollen production; diameter of pollen grains; and nectarproduction. Certain plants contained a transgenic marker thatenabled the vigour of their pollen to be quantified by screeningthe progeny from post-pollination trials against conventionalmale competitors. Plant size was strongly affected by plantdensity; plants in the lowest density pots comprised ten-timesmore dry biomass than individuals in the highest density pots.However, none of the attributes of individual flowers variedwith density. In contrast, the number of flowers per plant declinedrapidly with density. In the face of resource scarcity, theplants apparently conserved flower size rather than flower number.There was no difference in the response to density between transgenicand conventional plants, but transgenic plants obtained morefertilizations than expected in post-pollination competitionagainst conventional competitors. A separate experiment demonstratedthat B. napus is, nevertheless, capable of plasticity in certainflower attributes (petal size, stamen length) in response todefoliation. Explanations for the stability of flower size relativeto flower number are discussed. Copyright 2001 Annals of BotanyCompany Brassica napus, defoliation, density effects, flowers, flower size, intraspecific competition, nectar production, oilseed rape, pollination, transgenic plants     

Use of visual and olfactory cues of flowers of two brassicaceous species by insect pollinators

1. Pollinating insects exploit visual and olfactory cues associated with flower traits indicative of flower location and reward quality. Pollination can induce changes in these flower-associated cues, thereby influencing the behaviour of flower visitors. 2. This study investigated the main cues exploited by the syrphid fly Episyrphus balteatus and the butterfly Pieris brassicae when visiting flowers of Brassica nigra and Raphanus sativus plants. Whether pollen is used as a cue and whether pollination-induced changes affect flower volatile emission and the behavioural responses of the two pollinator species were also studied. 3. Pollinator preference was investigated by offering visual and olfactory cues individually as well as simultaneously in two-choice bioassays. Plant treatments included emasculation, hand-pollination and untreated control plants. The composition of flower volatiles from pollinated and unpollinated control plants was analysed by gas chromatography-mass spectrometry. 4. Both pollinators exhibited a strong bias for visual cues over olfactory cues. Neither pollinator used pollen as a cue. However, E. balteatus discriminated between newly opened and long-open flowers at short distance only when pollen was available. Flower visits by pollinators were influenced by pollination-induced changes in B. nigra but not R. sativus flowers. Pieris brassicae only responded to pollination-induced changes when visual and olfactory cues were offered simultaneously. The blend of volatiles emitted by B. nigra, but not R. sativus inflorescences was affected by pollination. 5. Collectively, the findings of this study show that different pollinators exploit different visual and olfactory traits when searching for flowers of two brassicaceous plant species.     

Changes in ethylene production and 1-aminocyclopropane-1-carboxylic acid content of pollinated carnation flowers

Pollination of flowers of standard carnation (Dianthus caryophyllus L. cv. White Sim) with pollen from flowers of miniature carnations (D. caryophyllus L. cv. Exquisite) caused them to wilt irreversibly within 1 to 2 days. Pollination stimulated a sequential increase in ethylene production by stigmas, ovaries, receptacles, and petals of the flowers. The ACC content of the stigmas increased rapidly in the first few hours after pollination. The possibility that subsequent production of ethylene by other parts of the flower is stimulated by translocated ACC is discussed. Ethylene production and ACC content of other parts of the flower reached their maximum 24 h after pollination. The petal tissues contributed the bulk of the ethylene productionper flower thereafter. There appears to be a qualitative difference between the enzyme in the stigmas converting ACC to ethylene and that in other parts of the flower.     

Presence of two types of flowers with respect to nectar sugar in two gregariously flowering species

Many species of animal-pollinated flowers are known to vary widely in the nectar content of flowers. Some proportion of flowers in many species is apparently nectarless, and such flowers are believed to be ‘cheaters’. Cheating may explain a part of the variability in nectar content. If cheating exists as a qualitatively different strategy then we expect bimodality in the distribution of nectar content of flowers. It has been shown in a multispecies study that gregarious species have a higher proportion of cheater flowers. We studied the frequency distribution of total nectar sugar in two gregariously flowering species Lantana camara and Utricularia purpurascens, which differed in other floral and ecological characters. At the population level, both the species showed significant bimodality in the total sugar content of flowers. The obvious sources of heterogeneity in the data did not explain bimodality. In Lantana camara, bimodality was observed within flowers of some of the individual plants sampled. In Utricularia purpurascens the proportion of nectarless flowers was more in high-density patches, suggesting that the gregariousness hypothesis may work within a species as well. The results support the hypothesis of cheating as a distinct strategy since two distinct types of flowers were observed in both the species. The effect of density in Utricularia purpurascens also supports the gregariousness hypothesis.     

Where have all the blue flowers gone: pollinator responses and selection on flower colour in New Zealand Wahlenbergia albomarginata

Although pollinators are thought to select on flower colour, few studies have experimentally decoupled effects of colour from correlated traits on pollinator visitation and pollen transfer. We combined selection analysis and phenotypic manipulations to measure the effect of petal colour on visitation and pollen export at two spatial scales in Wahlenbergia albomarginata. This species is representative of many New Zealand alpine herbs that have secondarily evolved white or pale flowers. The major pollinators, solitary bees, exerted phenotypic selection on flower size but not colour, quantified by bee vision. When presented with manipulated flowers, bees visited flowers painted blue to resemble a congener over white flowers in large, but not small, experimental arrays. Pollen export was higher for blue flowers in large arrays. Pollinator preference does not explain the pale colouration of W. albomarginata, as commonly hypothesized. Absence of bright blue could be driven instead by indirect selection of correlated characters.     

The suitability ofTeleonemia harleyi for biological control ofLantana camara in Australia

The tingidTeleonemia harleyi Froeschner from Trinidad is known to destroy the flowers ofLantana camara L. and so prevent seed formation. Colonies caged on plants destroy all flowers. Studies on the host range ofT. harleyi indicate that it is highly specific, feeding and ovipositing only onL. camara. It attacks all pest taxa ofL. camara naturalized in Australia and should be a valuable addition to the biological control complex. It was approved for liberation in Australia in September 1972.