Synchronized dichogamy and dioecy in neotropicalLauraceae

In hermaphrodite neotropicalLauraceae a highly evolved dichogamous system is present which represents a kind of temporal dioecy. This system involves the existence of two flower morphs which are characterized by reciprocal phases of receptivity of the stigmas and pollen release. In some genera (Persea, Cinnamomum), nectar is produced as a reward for the flower visitors, while in other genera (Aniba, Clinostemon, Licaria), nectar is absent and pollen seems to be the only reward. This implies that in this case the flowers in the female stage must be deceptive flowers. In dioecious species of the generaOcotea andNectandra, both the male and female flowers attract the visitors with nectar. The pollen-ovule ratio of theLauraceae is comparatively low. — The type of reproductive system that characterizes theLauraceae, comprising functional dioecy, small, inconspicuously coloured flowers, pollination by small bees, and large, one-seeded fruits dispersed by birds, is quite prominent among trees of various families in the tropical lowland forest. The relationship between the different modes of flowering within theLauraceae and the causes for the correlation of their reproductive traits are discussed.     

Pollination ecology ofOxalis violacea (Oxalidaceae) following a controlled grass fire

Vernal grass fires may encourage profuse flowering in clonal, colonies ofOxalis violacea. Long-styled colonies appear to be more floriferous than short-styled colonies and set a greater number of capsules. Individual flowers of both morphs live one or two days, change position on their respective pedicels and advertise nectar concealed at the base of the floral throat. AlthoughDiptera, Hymenoptera, andLepidoptera forage for nectar, bees (Andrenidae,Anthophoridae, Halictidae, andMegachilidae) probably make the only effective pollen transfers between the two morphs. Both male and female bees may transport pollen of both morphs and short-tongued bees (e.g.,Augochlorella spp.,Dialictus spp.) may be more common but as effective as pollinators as long-tongued bees (e.g.,Calliopsis andreniformis andHoplitis spp.). The conversion rate of flowers into capsules is only 13–17%. The spreading style in the short-styled morph is interpreted as an adaptation restricting insect-mediated, self-pollination but encouraging bee-stigma contact during nectar foraging.     

Honeydew feeding in the solitary bee Osmia bicornis as affected by aphid species and nectar availability

Like honey bees (Apis mellifera), non-Apis bees could exploit honeydew as a carbohydrate source. In addition to providing carbohydrates, this may expose them to potentially harmful plant products secreted in honeydew. However, knowledge on honeydew feeding by solitary bees is very scarce. Here we determine whether the polylectic solitary bee Osmia bicornis (=O. rufa) collects honeydew under semi-field conditions, and whether this is affected by aphid species and presence of floral nectar. Bees were provided with oilseed rape plants containing flowers and/or colonies of either Myzus persicae or Brevicoryne brassicae. We used the total sugar level of the bee crop as a measure of the individual's nutritional state and the oligosaccharide erlose as indicator for honeydew consumption. Erlose was present in honeydews from both aphid species, while absent in oilseed rape nectar, nor being synthesized by O. bicornis. When bees were confined to a single honeydew type as the only carbohydrate source, consumption of M. persicae honeydew was confirmed for 47% of the bees and consumption of B. brassicae honeydew for only 3%. Increased mortality in the latter treatment provided further evidence that B. brassicae honeydew is an unsuitable food source for O. bicornis. All bees that were given the choice between honeydew and floral nectar showed significantly increased total sugar levels. However, the fact that no erlose was detected in these bees indicates that honeydew was not consumed when suitable floral nectar was available. This study demonstrates that honeydew exploitation by O. bicornis is dependent on honeydew type and the presence of floral nectar.     

The movement patterns of carpenter beesXylocopa micans and bumblebeesBombus pennsylvanicus onPontederia cordata inflorescences

The movement patterns of carpenter bees (Xylocopa micans) and bumblebees (Bombus pennsylvanicus) foraging for nectar on vertical inflorescences ofPontederia cordata were studied near Miami, Florida. The floral biology ofP. cordata is unique in several ways: (a) many short-lived flowers per inflorescence, (b) constant nectar production throughout the life span of each flower, and (c) abscence of vertical patterning of nectar and age of flowers. Inflorescences ranged between 3.5 and 15.8 cm long and had between 9 and 55 open flowers. Both carpenter bees and bumblebees arrived mostly on the bottom third of the inflorescence and left after visiting flowers on the top third of the inflorescence. The departure position from the inflorescence was higher up than observed in studies of other insect pollinators foraging on other speces of plants. This pattern of departure probably occurs in the absence of a vertical gradient of nectar or floral morphology.     

Preference of cabbage white butterflies and honey bees for nectar that contains amino acids

Summary Amino acids occur in most floral nectars but their role in pollinator attraction is relatively unstudied. Nectars of butterfly-pollinated flower tend to have higher concentrations of amino acids than do flowers pollinated by bees and many other animals, suggesting that amino acids are important attractants of butterflies to flowers. In order to determine whether amino acids are important in attracting butterflies and bees, we tested the preference of cabbage white butterflies (Pieris rapae) and honey bees (Apis mellifera) by allowing them to feed from artificial flowers containing sugar-only or sugar-amino acid mimics ofLantana camara nectar. Honey bees and female cabbage white butterflies consumed more sugar-amino acid nectar than sugar-only nectar. In addition, female cabbage white butterflies visited artificial flowers containing sugar-amino acid nectars more frequently than flowers containing sugar-only nectars; honey bees spent more time consuming the sugar-amino acid nectar. Male cabbage white butterflies did not discriminate between the two nectars. These results support the hypothesis that the amino acids of nectar contribute to pollinator attraction and/or feeding.     

Flower choice by honey bees (Apis mellifera L.): sex-phase of flowers and preferences among nectar and pollen foragers

Bees foraging for nectar should choose different inflorescences from those foraging for both pollen and nectar, if inflorescences consist of differing proportions of male and female flowers, particularly if the sex phases of the flowers differ in nectar content as well as the occurrence of pollen. This study tested this prediction using worker honey bees (Apis mellifera L.) foraging on inflorescences of Lavandula stoechas. Female flowers contained about twice the volume of nectar of male flowers. As one would predict, bees foraging for nectar only chose inflorescences with disproportionately more female flowers: time spent on the inflorescence was correlated with the number of female flowers, but not with the number of male flowers. Inflorescence size was inversely correlated with the number of female flowers, and could be used as a morphological cue by these bees. Also as predicted, workers foraging for both pollen and nectar chose inflorescences with relatively greater numbers of both male and female flowers: time spent on these inflorescences was correlated with the number of male flowers, but not with the number of females flowers. A morphological cue inversely associated with such inflorescences is the size of the bract display. Choice of flowers within inflorescences was also influenced predictably, but preferences appeared to be based upon corolla size rather than directly on sex phase.     

Pollen and nectar as a reward in the basal epidendroid Psilochilus modestus (Orchidaceae: Triphoreae): A study of floral morphology, reproductive biology and pollination strategy

Psilochilus modestus Barb. Rodr. is a basal epidendroid orchid occurring in both the semi-deciduous and Atlantic rain forests of the state of São Paulo, southeastern Brazil. This species presents a perfect flowering synchrony within populations, since all the mature buds of each plant open simultaneously in the morning hours of the same day. These flowers are available only for 1 day and are pollinated by several species of small solitary and social native bees. These bees exploit both pollen and nectar as a reward. The bees collecting pollen promote a higher fruit set and perform mainly self-pollination while those collecting nectar, which are less numerous, are responsible for an increase in cross-pollinations. P. modestus is self-compatible but pollinator dependent. Natural fruit set (open pollination) is low when compared with the numbers obtained under manual self- and cross-pollination. Low fruit set in natural conditions is related to deficient pollen transfer, and pollinator inefficiency seems to be the main factor. Some factors, such as the small amount of nectar produced, the low number of flowers per inflorescence and their availability for 1 day only added to the perfect flowering synchrony seem to be responsible for the increase of cross-pollinations. The offering of both pollen and nectar as a reward can represent a transitional condition in basal Epidendroideae. Based on floral morphology, reward production and pollinator behavior, the relationship of P. modestus with the basal and most derived groups within Orchidaceae is discussed.     

Reward partitioning in Capparis spp. along ecological gradient

Summary The genus Capparis is represented in Israel by three taxons of the section spinosa. The pollinators of the three taxa are hawkmoths, crepuscular bees of the genus Proxylocopa and various daily bees. However, the efficiency of the different pollinators is very varied with respect to the individual taxons. Hawkmoths were frequently observed as pollinators of C. spinosa var. aravensis and C. ovata, but rarely on C. spinosa var. aegyptia. All the other bees, on the other hand, were found abundantly on all three taxons, all over the country. The three taxa all provide different rewards for their particular pollinators. Bees visiting C. spinosa var. aegyptia are provided with a lot of pollen but a relatively small amount of nectar, with a low sugar content. C. spinosa var. aravensis and C. ovata (the flowers visited more by hawkmoths), have less pollen but a higher amount of nectar which has a higher concentration of sugar. In drier habitats the emphasis of the reward provided by the flowers is nectar, whilst in the Mediterranean habitats it is the pollen which is the reward, without any connection to the systematic origin of the plant.     

Contrasting breeding systems in twoEriotheca (Bombacaceae) species of the Brazilian cerrados

The pollination biology and breeding systems ofEriotheca pubescens andE. gracilipes have been studied. These two species occur as trees in cerrado vegetation, the neotropical savannas of Central Brazil, with partially sympatric distributions. They have similar phenology and floral structure, although the flowers ofE. pubescens are larger. Both species have nectar flowers pollinated by largeAnthophoridae bees but the main pollinators of each species differ in size. The species have markedly different breeding systems: late-acting self-incompatibility inE. gracilipes and apomixis stimulated by pollination inE. pubescens.     

The foraging behaviour of a nectar feeding marsupial,Petaurus australis

Summary The foraging behaviour of non-flying nectar feeding mammals has been examined rarely. The exudivorous yellow-bellied glider (Petaurus australis) was observed to feed extensively (70% of the total feeding observation time) on the nectar of all species of Eucalyptus present at a site in southeastern Australia. Gliders harvested nectar, and presumably pollen also, whenever eucalypt flowers were available and selected trees with 2–3 times as many flowers as that on trees randomly selected along a transect. The abundance of flowering trees varied temporally and, at times when few flowering trees were present, gliders chose trees with fewer flowers than at times when flowering trees were abundant. When flowering trees were superabundant or scarce, there was no relationship between the number of flowers in a tree and the duration of visits by gliders. However, at intermediate levels of abundance, the amount of time a glider spent in a tree was related to the number of flowers in a tree. Gliders devoted 90% of the time outside their dens to foraging and the above relationship is suggested to reflect two foraging options which maximize net energy gain for different abundances of flowering trees. Although gliders spent considerable lengths of time in individual trees feeding, initial deposition of cross pollen when gliders first arrive in a tree may be substantial and thus, may provide significant amounts of outcrossing for these eucalypts.     

The role of insect water balance in pollination ecology: Xylocopa and Calotropis

Summary Two carpenter bees (Xylocopa spp.) in southern Israel both use the asclepiad Calotropis procera as a primary nectar source. This plant genus is coevolved with carpenter bees, and aspects of the insect-flower interaction in Israel suggest that the smaller bee, X. sulcatipes, is the natural co-adapted pollinator, a view borne out by the geographical distributions of the species concerned. There are significant mismatches between the plant and the larger X. pubescens, involving physical fit and behaviour. These mismatches are particularly evident when the physiologies of the bees and the plant are considered. The different sizes and colours of the two bees lead to different daily activity patterns, only X. sulcatipes being thermally suited to, and thus abundant at, times of maximum nectar production by Calotropis. Similarly the water requirements of X. sulcatipes are finely balanced with the water production in the floral nectar; this bee gains just enough water when foraging to restore its blood concentration and production in the floral nectar; for deposition in the nest. X. pubescens does not incur net water loss in flight and gains too much water from Calotropis flowers, necessitating copious urination and tonguelashing. Hence physiological information can be of use in deciphering insect-plant coevolutionary patterns, and the water component of nectar is confirmed as a potentially major determinant of foraging activities. The circumstances where this will be particularly true, and cases where it may not apply, are discussed.     

Dispersal of Eucalyptus torelliana seeds by the resin-collecting stingless bee,Trigona carbonaria

Ants are the only group of invertebrates currently identified as significant dispersers of seeds, but we report here the dispersal of Eucalyptus torelliana seeds by bees. Fruits of E. torelliana produce resin which is collected by workers of the stingless bee Trigona carbonaria. Seeds adhere to resin in the workers' corbiculate and are transported to the nest. Workers transported seeds distances of more than 300 m from the parent tree and seeds at the nest were viable and capable of germination. Seeds were removed from the nests by workers and discarded away from the nest, and E. torelliana trees became established in the vicinity of colonies of T. carbonaria. Mellitochory may be a novel method of seed dispersal where bees are dispersers, and associated with fruits that produce resin as an attractant for bees.     

Reproductive ecology of tropical forest trees in logged and fragmented habitats in Thailand and Costa Rica

Invertebrates mediate several important ecological processes, including pollination and seed predation, and events that affect invertebrate diversity or behaviour can potentially disrupt forest regeneration processes. This study investigates the impact of logging in Thailand and forest fragmentation in Costa Rica on the pollination and seed production of two self-incompatible forest trees. Logging in a dry deciduous dipterocarp forest in Thailand resulted in reduced densities of the common dipterocarp treeShorea siamensis and variably isolated individual trees. The number of flower visits to S. siamensis by pollinating Trigona bees was not affected by logging disturbance. However, pollinators did spend longer periods of time foraging in the canopies of isolated trees which were more prevalent in logged areas where tree density had been reduced. Consequently, at the logged site few cross-pollinations were effected and fruit set of S. siamensis was considerably lower than at nearby unlogged sites where distances between flowering conspecifics were smaller. Reduced fruit set has long-term implications for the recovery of S. siamensis populations in disturbed areas, and local population genetic structure is likely to be affected as reduced outcrossing rates among trees in disturbed regions results in relatively inbred seed. In Costa Rica forest fragmentation has restricted the once widespread tree Anacardium excelsum to forest patches located in an agriculturally-dominated landscape. As with S. siamensis, the abundance of pollinators, also Trigona bees, in the canopies of A. excelsum was largely unaffected by fragment size. Nevertheless, pollination success and seed production was positively correlated with fragment size. We propose that small bees rarely move between forest fragments and gene exchange through pollination occurs predominantly among trees within fragments and, together with likely low genetic variability in small fragments, that this contributes to the observed reduced fertilisation and seed set of A. excelsum. Thus increased tree isolation tree through selective logging or habitat fragmentation by forest clearance can result in reduced seed set due to changes in the foraging patterns of poorly mobile pollinators. Even if population sizes of the pollinators are maintained following environmental perturbation, this study shows that disturbance may disrupt pollination processes through changes in pollinator foraging behaviour. More attention needs to be focussed on changes in the behaviour of species involved in key ecological interactions following disturbance events in tropical forests.     

Nectar flow and pollinators' efficiency in two co-occurring species ofCapparis (Capparaceae) in Israel

Two closely related species ofCapparis, C. ovata andC. spinosa, which are exposed to the same pollination environment were studied. The nectar volume and concentration ofC. ovata are higher than inC. spinosa. Both species have similar pollination efficiency, but the relative contribution of each pollinator is different.C. ovata is pollinated mainly hy hawkmoths while the principal pollinators inC. spinosa are bees.     

Choice of food resource by bees and ants (Hymenoptera: Apoidea,Formicidae) on coconut tree inflorescences (Cocos nucifera,Arecaceae)

Coconut trees are mostly anemophilous; however, because bees and ants forage on coconut tree inflorescences for floral food, entomophilous pollination can also occur. The aim of this study was to determine the food resource preference of bees and ants while they collect pollen, nectar and, for ants, occasionally prey on coconut tree inflorescences, as well as to evaluate their impact on self-pollination. The number of ant visits to first female and then male flowers is significantly higher than that of bees. For Apis mellifera (L.) and Pseudomyrmex gracilis (Fabricius) 14% of the sequences were favorable to direct self-pollination. The probability of visits for all of the sequences was similar for both bees and ants and there was no difference in resource choice. For these reasons, neither can be considered a more effective pollinator of the coconut tree.     

Old comb for nesting site recognition by <Emphasis Type="Italic">Apis dorsata?</Emphasis> Field experiments in China

The Asian giant honey bee, Apis dorsata, often conducts seasonal, long-distance migrations in southern China, between a preferred tree (having more than one nest) and alternate sites. Although worker bees cannot make a round-trip journey, colonies re-utilize preferred trees after an absence of several months. We performed comb experiments in which bases and all abandoned combs were entirely scraped off trees and their sites covered with plastic, or comb was moved to trees of the same species. Swarms of giant honey bees investigated trees where combs were removed and continued to nest on the same trees. In contrast, placing combs in nets on previously used trees, or on nearby trees of the same species, did not attract more swarms. The same number of colonies that left them returned to previously occupied trees. Our findings suggest that direct olfactory or sensory contact with old comb bases might regulate nest establishment, but individual trees, lacking normal visual or chemical cues of old nests, are relocated using behavioral devices that remain to be elucidated. Received 12 February 2007; revised 5 June 2007; accepted 13 September 2007.     

Floral mimesis inThelymitra nuda (Orchidaceae)

Insect pollination occurred inThelymitra nuda R. Br. on sunny days when the ambient temperature exceeded 20 °C. The flower buds on a raceme opened subsynchronously displaying the brightly-colored, actinomorphic perianth and exposed the contrastingly-colored, scented and ornamented column. InT. nuda the staminodes and the filament of the fertile stamen are fused to one another producing an inflated hood over the anther. This staminodal hood is terminated in two non-ornamental, but brightly-colored, central lobes and two terete lateral lobes bearing approximately 400 white trichomes. Each trichome bears a double chain of 30–40 spherical, rugulose cells. Female bees, in the genusLasioglossum (Halictidae), were observed to land directly on the hood and curled their bodies around the four lobed tip of the staminodal complex. The bees attempted to forage on the lobes as if they were collecting pollen from fertile, poricidal stamens. These bees applied thoracic vibration to the yellowish central lobes and actively scraped the trichome clusters (Pseudopollen) with their forelegs. Bees carried the pollinaria ofT. nuda dorsally on their abdomens. Abdominal contact with the rostellum appeared to occur when the female bee disengaged herself from the staminodal hood. Observations made of bees on co-blooming flowers, and analyses of pollen loads collected by bees suggested that the orchid flower mimics the guild of blue-purple flowers that lack floral nectar but offer pollen in poricidal anthers. The models ofT. nuda are co-bloomingLiliaceae in the generaDichopogon andThysanotus. However, nectarless, buzz-pollinated flowers are also extensively distributed over the orchid’s range. More than 30% of the flowers in theT. nuda population had their pollinaria removed, suggesting a high capacity for cross-pollination in an orchid genus usually considered to be self-pollinated via mechanical autogamy. This study confirmed previous predictions that column modifications represented a trend towards pseudanthery.     

Morpho-ecological aspects on the pollination ofCalotropis procera (Asclepiadaceae) in Israel

Calotropis procera (Asclepiadaceae) grows in Israel under extremely hot climatic conditions. Flower morphology is adapted towards the concealment of nectar, in order to protect it against robbery by ants and from evaporation. Pollinia while being inserted within the stigmatic chamber, are soaked in the liquid nectar which, by its concentration controls pollen germination. Two Carpenter bees (Xylocopa) are the only pollinators and their behavior on flowers is discussed.     

Stamen movements in flowers ofOpuntia (Cactaceae) favour oligolectic pollinators

Opuntia brunneogemmia andO. viridirubra occur sympatrically in the Serra do Sudeste, Rio Grande do Sul, Brazil. Their flowers have 450–600 thigmonastic stamens and provide large amounts of pollen and nectar for bees. Bees of 41 species were registered at the flowers ofO. brunneogemmia and 30 at the flowers ofO. viridirubra. Females of three oligolectic species are the only effective pollinators:Ptilothrix fructifera (Anthophoridae),Lithurgus rufiventris (Megachilidae), andCephalocolletes rugata (Colletidae). During their visits inOpuntia-flowers, bees touch the filaments and stimulate the movement of the stamens to the centre of the flower. At the end of this movement, the anthers are densely packed around the style. As a consequence the pollen is presented in an easily accessible upper layer of anthers and various, nearly inaccessible lower layers. The lower layers contain about 80% of the pollen reward. Only females of the three oligolectic pollinators exploit the pollen from the lower layers and reach the nectar furrow. Therefore, through their stamen movements,Opuntia flowers hide most of their pollen from flower visitors but favour effectively pollinating, oligolectic bees.     

Observations on the big bang flowering of Miconia minutiflora (Melastomataceae)

Trees ofMiconia minutiflora produced abundant flowers for only one to three days during mid-April 1983 in the vicinity of Saül, French Guiana. They attracted large numbers of at least 14 species of bees that collected nectar or pollen or both. Nectar production is uncommon in the Melastomataceae and not previously reported forMiconia. Peak bee activity at the trees was in the morning and by afternoon most visits were limited to those bees in search of remnant pollen, especially species ofTrigona. As has been shown for other neotropical plants, heavy rains may trigger flowering in this species. It is suggested that the flowering system ofM. minutiflora promotes outcrossing because of interactions among the numerous species of bees visiting the trees and because of inter-individual variation in nectar and pollen availability. Therefore, bees may fly to other trees instead of becoming satiated with nectar or pollen from a single tree.