Search

• Honey bees increased yield for five commonly planted blueberry varieties • Blueberry yields still show a pollen deficit • Honey bees can be effective pollinators of blueberries in areas which lack bumble bees • Benefit of bees and pollination deficit differs between varieties Agricultural crops are often dependent on insect pollination for commercially viable yields. Blueberries are an example of such a crop and owing to their proposed health benefits they are grown around the world, including locations where their native bumble bee pollinators do not occur. In the absence of bumble bees, blueberry pollination in South Africa and many other parts of the non-native, commercial range is performed primarily by honey bees. Despite this, the effectiveness of honey bee pollination on blueberries remains understudied. This study determined the effect of honey bee pollination on components of fruit yield (fruit set and mass) of five blueberry varieties that are extensively planted in South Africa. For each variety, two metrics were calculated: 1) the benefit of bees — a comparison of fruit yields after exposure to honey bees and fruit yields after honey bee exclusion, 2) the pollination deficit — the difference in yield between hand pollination (maximum yield potential) and yields after exposure to honey bee pollinators. Honey bee pollination consistently resulted in improved yields, although the magnitude of this improvement (i.e., the benefit of bees) was dependent on the variety considered. Similarly, the pollination deficit also varied considerably across varieties and while some varieties appeared to perform close to maximum potential (small pollination deficit), others yielded well below their maximum potential under honey bee pollination. This study demonstrates that honey bees are functional pollinators of blueberries in areas where native blueberry pollinators are absent. However, in such areas, it is important that special focus is given to selecting blueberry varieties that perform well with honey bees as their primary pollinator. Further research is necessary to determine how the pollination deficit of blueberry varieties can be decreased as well as how to increase the effectiveness of honey bee pollination. [ABSTRACT FROM AUTHOR]

• Honey bees significantly increase yield in blueberry variety Ventura. • Blueberry yields still show a pollen deficit. • Honey bees can be effective pollinators of blueberries in areas which lack bumble bees. Animal-mediated pollination is an essential ecosystem service on which over a third of the world's agricultural crops depend. Blueberry fruit production is highly dependent on animal pollination and although visited by a range of bee species in their native range and agricultural settings, bumble bees are thought to be their primary native pollinators. Demand for blueberries has increased in recent years due to their perceived health benefits. Consequently, blueberry cultivation has expanded well beyond their native and original agricultural range, including several regions where bumble bees are not present. In South Africa, like many areas in the world, honey bees are the only commercially available pollinators for blueberries because many countries ban the importation of bumble bees. This study aimed to determine the benefits of honey bee pollination on blueberry fruit yield for the variety Ventura by comparing yields of honey bee-pollinated flowers to flowers where pollinators were excluded. Our results show that honey bees significantly increased berry mass and diameter. We conclude that Ventura in South Africa can be pollinated by honey bees, and that honey bee pollination can be an effective substitute for bumble bees in areas where bumble bees are unavailable. We also determined the extent to which blueberry yields could be improved by comparing fruit yield under honey bee pollination to fruit yield achieved through hand pollination. We found that honey bee pollinated blueberry yields were lower than yields achieved through hand pollination, suggesting that there is potentially room to improve honey bee pollination. Furthermore, we offer a conceptual figure to demonstrate how yield obtained through pollinator exclusion, open pollination, and hand pollination relate to each other. Additional research is required to study how beneficial honey bees are to fruit yield on other blueberry varieties as the benefits of honey bees are likely to vary depending on the variety. [ABSTRACT FROM AUTHOR]

The striking variation in flower color across and within Angiosperm species is often attributed to divergent selection resulting from geographic mosaics of pollinators with different color preferences. Despite the importance of pollinator mosaics in driving floral divergence, the distributions of pollinators and their color preferences are seldom quantified. The extensive mass-flowering displays of annual daisy species in Namaqualand, South Africa, are characterized by striking color convergence within communities, but also color turnover within species and genera across large geographic scales. We aimed to determine whether shifts between orange and white-flowered daisy communities are driven by the innate color preferences of different pollinators or by soil color, which can potentially affect the detectability of different colored flowers. Different bee-fly pollinators dominated in both community types so that largely non-overlapping pollinator distributions were strongly associated with different flower colors. Visual modeling demonstrated that orange and white-flowered species are distinguishable in fly vision, and choice experiments demonstrated strongly divergent color preferences. We found that the dominant pollinator in orange communities has a strong spontaneous preference for orange flowers, which was not altered by conditioning. Similarly, the dominant pollinator in white communities exhibited an innate preference for white flowers. Although detectability of white flowers varied across soil types, background contrast did not alter color preferences. These findings demonstrate that landscape-level flower color turnover across Namaqua daisy communities is likely shaped by a strong qualitative geographic mosaic of bee-fly pollinators with divergent color preferences. This is an unexpected result given the classically generalist pollination phenotype of daisies. However, because of the dominance of single fly pollinator species within communities, and the virtual absence of bees as pollinators, we suggest that Namaqua daisies function as pollination specialists despite their generalist phenotypes, thus facilitating differentiation of flower color by pollinator shifts across the fly pollinator mosaic. [ABSTRACT FROM AUTHOR]

Recent studies have shown that mutualisms often have variable outcomes in space and time. In particular, the outcomes may be dependent on the density of the partners with unimodal or saturating outcomes providing stability to the mutualism. We examine density-dependent outcomes of an obligate, species-specific mutualism between a South African carnivorous plant ( Roridula dentata) and a hemipteran ( Pameridea) that facilitates prey digestion, but also sucks plant sap. Plants occur in sandy, leached, nitrogen-poor soils and have no digestive enzymes to digest prey. Instead they rely on obligately dependent hemipterans to supply nitrogen by digesting prey for them and defecating on their leaves. We documented the densities of Pameridea on Roridula in the field. In the greenhouse, we manipulated the hemipteran densities on Roridula and measured the mean relative growth rates of plants with differing hemipteran densities. Plants exhibited a unimodal response to the density of their mutualist partners. Those with no hemipterans had negative growth rates, suggesting that hemipterans are important in facilitating nitrogen absorption. Plants with intermediate hemipteran densities had positive growth rates but growth rates were negative under very high hemipteran densities. Our research provides support for variable and unimodal outcomes in mutualism. Unimodal outcomes may be particularly important in obligate mutualisms and this is one of the few studied outside of pollinating seed parasite mutualisms. In this system, extrinsic factors such as other predators may affect the mutualism by altering the numbers of hemipterans. [ABSTRACT FROM AUTHOR]

The author relates his opinion on the inability of the National Research Foundation (NRF) to administer and allocate funding for research in South Africa. He was amazed that the NRF cannot do simple computation in tallying records of researchers and allocating correct funding. He states that the NRF must be fixed due to a lack of capacity and poor management.

Although the tremendous variability in floral colour among angiosperms is often attributed to divergent selection by pollinators, it is usually difficult to preclude the possibility that floral colour shifts were driven by non-pollinator processes. Here, we examine the adaptive significance of flower colour in Disa ferruginea, a non-rewarding orchid that is thought to attract its butterfly pollinator by mimicking the flowers of sympatric nectar-producing species. Disa ferruginea has red flowers in the western part of its range and orange flowers in the eastern part--a colour shift that we hypothesized to be the outcome of selection for resemblance to different local nectar-producing plants. Using reciprocal translocations of red and orange phenotypes as well as arrays of artificial flowers, we found that the butterfly Aeropetes tulbaghia, the only pollinator of the orchid, preferred both the red phenotype and red artificial flowers in the west where its main nectar plant also has red flowers, and both the orange phenotype and orange artificial flowers in the east, where its main nectar plant has orange flowers. This phenotype by environment interaction demonstrates that the flower colour shift in D. ferruginea is adaptive and driven by local colour preference in its pollinator.

Background and Aims: Floral variation, pollination biology and mating patterns were investigated in sunbird-pollinated Babiana (Iridaceae) species endemic to the Western Cape of South Africa. The group includes several taxa with specialized bird perches and it has been proposed that these function to promote cross-pollination., Methods: Pollinator observations were conducted in 12 populations of five taxa (B. ringens subspp. ringens, australis, B. hirsuta, B. avicularis, B. carminea) and geographic variation in morphological traits investigated in the widespread B. ringens. Experimental pollinations were used to determine the compatibility status, facility for autonomous self-pollination and intensity of pollen limitation in six populations of four taxa. Allozyme markers were employed to investigate mating patterns in four populations of three species., Key Results: Sunbirds were the primary pollinators of the five Babiana taxa investigated. Correlated geographical variation in perch size, flower size and stigma-anther separation was evident among B. ringens populations. Experimental pollinations demonstrated that B. ringens and B. avicularis were self-compatible with variation in levels of autonomous self-pollination and weak or no pollen limitation of seed set. In contrast, B. hirsuta was self-incompatible and chronically pollen limited. Estimates of outcrossing rate indicated mixed mating with substantial self-fertilization in all species investigated., Conclusions: Despite the possession of specialized bird perches in B. ringens and B. avicularis, these structures do not prevent considerable selfing from occurring, probably as a result of autonomous self-pollination. In eastern populations of B. ringens, smaller flowers and reduced herkogamy appear to be associated with a shift to predominant selfing. Relaxed selection on perch function due to increased selfing may explain the increased incidence of apical flowers in some populations.

Birds may hover over or perch on flowers when feeding on nectar, and this assists cross-pollination if they then visit other plants. Here we investigate the curious sterile inflorescence axis of the South African Cape endemic 'rat's tail' plant (Babiana ringens, Iridaceae), whose function--unlike in other bird-pollinated plants--is exclusively to provide a perch for foraging birds. We find that this structure promotes the plant's mating success by causing the malachite sunbird (Nectarinia famosa), its main pollinator, to adopt a position ideal for the cross-pollination of its unusual ground-level flowers.