Abundance Of Flower Visitors Research Articles

Breeding system and spatial variation in the pollination biology of the heterocarpic Thymelaea velutina (Thymelaeaceae)

Thymelaea velutina (Thymelaeaceae) is a unique dioecious and heterocarpic shrub, each female producing both dry and fleshy fruits. It is endemic to the Balearic Islands (western Mediterranean) and has suffered an important regression in recent decades, especially due to habitat loss. It lives in coastal areas, mainly in dunes, but a few populations occur up to 1300 m in the mountains of Mallorca. In the present study, we examined its breeding system and pollen vectors, determined whether seed production is pollen-limited, and quantified the relative importance of different insect visitors at coastal and mountain sites. Selective exclusions showed no differences between populations in the relative importance of insects and wind as pollen vectors. Pollen was limiting at both populations, though not consistently in time. Flowers of T. velutina were visited mostly by generalist insects, and species composition and abundance of flower visitors varied both in space and time. The flowering period is about a month later in the mountain than in the dune, and this results in a higher frequency of insect visits to plants in the mountain due to the higher insect abundance; insects were also more diverse in the mountain, although they visited a proportionally lower number of flowers than in the dune. Despite this spatio-temporal variation in the frequency of insect visits and in the importance of a particular insect group, the ambophilous system in this species (previously described as anemophilous) ensures a relatively high fruit set at the two different sites.

Spatio‐temporal variation in the pollination mode of Buxus balearica (Buxaceae), an ambophilous and selfing species: mainland‐island comparison

Mixed‐pollination systems may allow plants to achieve stable seed production when unpredictable conditions cause variation in the relative success of different pollination modes. We studied variation in time (two years) and space (in five populations, three from an island and two from mainland) in the pollination mode of Buxus balearica, an ambophilous (i.e. pollinated by wind and insects) and selfing species distributed in the Mediterranean Basin, by means of direct observations and experimental manipulations (bagging with different material). The relative importance of each pollination mode differed among populations; however, levels of selfing and wind pollination were similar between island and mainland. Flowers of B. balearica were visited only by generalist insects, and species composition and abundance of flower visitors varied both in space and time. Frequency of insect visits to plants were not higher in mainland than island populations, although insects on the mainland were more diverse, visited a proportionally greater number of flowers, and remained longer on the plants than insects on the island. Frequency of insect visits was negatively correlated with flowering synchrony (all populations pooled) and was found to increase seed set in one of the mainland populations (that with highest frequency of insect visits and highest flower visitation rate). Fruit and seed mass were found to be not affected by pollination mode. Scarcity of pollinators in the island seems to have an effect on the pollination mode, although the greatest variation in breeding system was found at a more local scale.

Connectance of Brazilian social bee: food plant networks is influenced by habitat, but not by latitude, altitude or network size

Several recent studies suggest that the level of generalization (measured as percentage connectance) of plant-pollinator networks has several ecological correlates, e.g. latitude and altitude. Here we report on levels of generalization in 27 two-mode networks of social bees and their food plants in various Brazilian habitats and urban environments. Social bees are generalist foragers and are among the most abundant flower visitors in Brazil. They probably account for 30-50% of all plant - flower visitor interactions. Connectance was significantly influenced by habitat. Cerrado forests showed lower connectance than the dry dune habitats, with Atlantic rain forest and urban sites taking intermediate position and arid Caatinga being similar to dunes. This shows that generalization in a plant - flower visitor community can be influenced by habitat even within a group of generalist flower visitors, in our case social bees. We show that the strength of the interactions is not different between Cerrado and semi-arid habitats (dunes and Caatinga) and discuss other explanations for our findings.

Path coefficient analysis of environmental factors influencing flight activity of Apis florea F. and seed yield in carrot (Daucus carota L.)

Foraging ecology of insect pollinators visiting carrot flowers (Daucus carota L.) was studied in relation to five environmental variables. The dwarf honeybee, Apis florea L., was the most abundant flower visitors and comprised more than 94% of the total flower visiting insects. Commencement of flight activity occurred when a minimum threshold of environmental variables was surpassed while the cessation was governed mainly by decline in values of light intensity and radiation. In between the commencement and cessation, the foraging population correlated significantly and positively with air temperature, light intensity, solar radiation and nectar-sugar concentration and negatively with relative humidity. Path coefficient analysis, however, revealed that direct effect of temperature was high and positive followed by light intensity and solar radiation while the direct effect of relative humidity was high and negative. The direct effect of nectar-sugar concentration was negative and negligible. Evidently, path coefficient analysis gave a more clear picture of effects than did the simple correlation analysis. Apis florea on an average visited 1.14+0.23 and 22.78+2.57 umbels and flowers/min, respectively during different hours of the day. Furthermore, the insect pollinated plots produced significantly more seeds with heavier weights than those isolated from insect visits.

Efeito da polinização por abelhas e outros insetos na produção de sementes de cebola

A deficiência de polinização tem sido apontada como uma das causas da baixa produção de sementes na cultura da cebola. O objetivo deste trabalho foi avaliar a relação da presença de abelhas e outros insetos em flores de duas cultivares de cebola, Allium cepa L. (Alliaceae), com a produção de sementes. Foram registradas a diversidade e a freqüência de insetos nas flores de cebola e o efeito polinizador foi testado. O comportamento de Apis mellifera foi observado diretamente nas flores e a fidelidade verificada a partir do pólen nas corbículas. Representantes de Hymenoptera e Diptera foram os visitantes florais mais abundantes. Houve correlação entre a freqüência de A. mellifera com número de umbelas com flores, em ambas cultivares, e de outros insetos em Crioula Alto Vale. A produção de sementes com livre visitação de insetos apresentou acréscimo superior a 20% em relação às parcelas sem insetos e com visita de uma abelha. A. mellifera transportou mais de 70% de pólen de cebola. A presença de A. mellifera é indispensável para a produção comercial de sementes de cebola.

FLORAL DISPLAY, POLLINATOR DISCRIMINATION, AND FEMALE REPRODUCTIVE SUCCESS IN TWO MONOECIOUSBEGONIASPECIES

In many plant species with unisexual flowers, the female flowers lack pol- linator rewards and are pollinated by visitors who mistake the female flowers for rewarding male flowers. Here we present the results of observations and experiments designed to investigate pollinator discrimination and its consequences for female reproductive success in two monoecious Begonia species pollinated by deceit. Male and female flowers of B. urophylla are similar in shape, but female flowers are smaller than male flowers, while in B. tonduzii, male and female flowers have strikingly different shapes, but their petaloid tepals are similar in total area. Flower visitors displayed marked discrimination against the rewardless female flowers of both species. Seven bee species were observed on B. urophylla, and for all species taken together the relative visitation rate to male flowers was 8.6 times that to female flowers. The bee Trigona fulviventris accounted for 95% of all visits to B. tonduzii and visited male flowers 15.4 times as often as female flowers. The flower visitors of B. urophylla varied significantly in their degree of discrimination against female flowers, with visitation rates to male flowers 3.7-21.8 times those to female flowers. The two most abundant flower visitors displayed the greatest discrimination against female flowers and, although they comprised nearly 54% of all visits, were responsible for only 15% of all visits to female flowers. Thus, the relative abundance of different flower visitors on B. urophylla is a poor predictor of pollinator importance. In both species the inflorescence sex ratio was male-biased early in the season and female-biased later. Hand-pollination experiments revealed that fruit set in B. tonduzii was pollinator limited both during peak and late flowering, with supplemental pollination having its greatest effect late in the season when male flowers were rare. In contrast, fruit set was only weakly affected by supplemental hand-pollination in B. urophylla. The significant pollinator limitation observed in B. tonduzii and the lack of it in B. urophylla are consistent with our observation that the visitation rate to female flowers was much higher in B. urophylla than in B. tonduzii, which was due in part to the lower level of pollinator discrimination against female flowers of B. urophylla. Our finding that female reproductive success is limited by pollinator visitation in B. tonduzii indicates an opportunity for the evolution of increased resemblance between male and female flowers in this species.

Bees and Other Insects Recorded on Flowering Trees in a Subtropical Araucaria Forest in Southern Brazil

Flower visiting insects were monitored on angiosperm trees in an Araucaria forest in Rio Grande do Sul, Brazil. The most abundant flower visitors were workers of the introduced honey bee, Apis mellifera, followed by stingless bees which were represented by 8 species. Together with other bees, they provide the main guild of foragers on flowering trees. The stingless bee fauna of the study area is similar to that of other regions of the Mata Atlântica, especially of former Araucaria forests, but also of montane coastal rain forests.

Resource Partitioning between Highly Eusocial Bees and Possible Impact of the Introduced Africanized Honey Bee on Native Stingless Bees in the Brazilian Atlantic Rainforest

The highly eusocial bee community of the neotropical Atlantic Rainforest was studied at Boracéia Biological Station in the state of São Paulo, Brazil. In this reserve, 17 species of stingless bees and the introduced Africanized honey bee were found, the latter being the most abundant flower visitor. Of all flowering plants, Asteraceae and Myrtaceae were particularly important as resources for bees. Trophic niche overlap between the various species of stingless bees is evident, and it was generally larger within the tribes Meliponini and Trigonini than between members of different tribes. Nevertheless, in the stingless bee community the competitive pressure is rather uniformly spread. The trophic niche of the Africanized honey bee can be positioned between those of Meliponini and Trigonini. Today this introduced species represents the main competitor in this bee community. However, its impact on native stingless bee populations is apparently buffered by mass-flowering trees which are the most important food plants of the indigenous highly eusocial bees.

Pollination of Cantaloupes Under Spun bonded Row Cover by Honey Bees (Hymenoptera: Apidae) in West Africa

We evaluated 2 pollination treatments which did not require removal of the cover on cantaloupes under small tunnels of Agryl in West Africa. The cover was removed from control plots at the onset of pistillate flowering but was maintained over treated plants for an additional 20 d. In the 1st treatment, one end of the tunnel was cut open to allow some access to pollinators. In the 2nd treatment, the tunnel was kept closed but was provided with a multiple-entrance hive. The cover did not affect production or concentration of nectar. Honey bees, Apis mellifera adansonii Latreille, flew under the cover in both treatments, with an average of 54% as many bees foraging under the tunnels opened at one end as in the control. However, muscid flies, which were the most abundant flower visitors in the open, hardly foraged under the cover. Pollination intensity and amount of cantaloupe pollen on the body of honey bee foragers in the 2 covered treatments were similar but were significantly greater than in the open. Total yield, fruit size, and seed content confirmed that pollination was at least as good in the covered plots as in the control. Covered plants produced more commercial-grade fruit than control plants, which received 6 insecticide applications, demonstrating the usefulness of these pollination treatments in combination with the row cover for integrated pest management.

Pollen movement to flowering canopies of pistillate individuals of three rain forest tree species in tropical Australia

AbstractThis study measured the quantities of effective pollen vectors and their pollen loads arriving at the canopies of dioecious tropical rain forest trees in north‐east Queensland. Population flowering synchrony, effective pollinator populations and pollen loads transferred between staminate and pistillate trees were compared among three insect‐pollinated tree species. All three were visited by a wide range of insects, 75% of which (mostly 3–6 mm long) carried conspecific pollen. Fewer than 8% of individual insects were found to be carrying single‐species pollen exclusively and none could be described as specialist pollen foragers. The introduced honeybee carried greater quantities of pollen than any native species but was not necessarily a reliable pollinator.The brief flowering periods in Neolitsea dealbata (3–4 weeks) and Litsea leefeana (4–5 weeks) populations were synchronized among individuals. Flowering in the Diospyros pentamera population extended over 15 weeks and most individuals were in flower for most of this period. Staminate trees began flowering earlier, produced more flowers and attracted relatively more insects than did pistillate trees, suggesting a density‐dependent response of pollinators to flowering performance. Pollen was trapped in greater quantities on insects at staminate trees than at pistillate trees.Insect numbers increased at peak flowering periods and Diptera were the most abundant flower visitors. Anthophilous Coleoptera were more numerous at staminate than at pistillate trees in all three tree species populations. Larger quantities of pollen were mobilized during peak flowering times although the greatest quantities were transferred to pistillate canopies towards the end of the population flowering periods. Diptera carried pollen more often to pistillate N. dealbata and L. leefeana trees than did other groups whereas Coleoptera carried pollen more often to pistillate D. pentamera trees. The two contrasting flowering performances in the three tree species are discussed with reference to mechanisms that facilitate pollen transfer between staminate and pistillate trees.

Insect pollination in the New Zealand mountain flora

Abstract A wide variety of lepidopterans, bees, flies, and beetles visit the flowers of most species of New Zealand montane plants. Of the 82 plant Species which were well-collected, 4 species (Pterostylis sp., Pratia macrodon, Mazus radicans, and Dracophyllum acerosum) exhibited specialised pollination relationships with an insect order; 3 species (Cyathodes fraserii, Microris unifolia, and Thelymitra venosa) are not apparently visited by insects; and the remaining 7S species are visited by a variety of insects in 2 or more orders. Introduced plant species in the Composite family are visited predominantly by introduced bumblebees. Bees in the genera Lasioglossum and Leioproctus are abundant flower visitors. The most common lepidopteran flower visitors are in the families Noctuidae, Geometridae, and Pyralidae, and the genus Lycaena. Dipterans, in particular tachinids and syrphids, are numerically the most abundant flower visitors, and visit a wide range of species. The syrphid Melangyna novaezelandiae vis...