Sending private messages: Floral ultraviolet signals are correlated with pollination syndromes in Erica

The presence of ultraviolet (UV, wavelengths between 300-400 nm) reflectance in insect-pollinated flowers has been linked to pollination efficiency and pollination shifts, but little is known about its prevalence and function in other pollination systems and African species. We chose the genus Erica for studying the prevalence of UV because of its extreme radiation (c. 680 species) in the Cape, South Africa, with a diversity of pollination syndromes. This study quantified the prevalence and brightness of UV reflectance for five Erica pollination syndromes and tested pollinator preferences for UV reflectance in the two groups with the highest prevalence: sunbirds and long-proboscid flies. Our results show that UV colouration is absent or rare in Erica species pollinated by unclassified insects, rodents or wind. About 17 % of bird-pollinated species reflected UV but choice experiments revealed that free-ranging sunbirds showed no preference for UV signals. All sampled long-proboscid fly-pollinated species reflected UV and its experimental removal decreased seed set drastically, suggesting that long-proboscid flies in the Cape strongly prefer or depend on UV and thereby contributed to selecting for the evolution of this signal.

DNA metabarcoding unveils the effects of habitat fragmentation on pollinator diversity, plant-pollinator interactions, and pollination efficiency in tropical islands

Habitat fragmentation is known to affect biodiversity, but the impact on pollinators and their interactions with plants is still unclear in anthropized landscapes. Islands are open-air laboratories for ecological studies with simplified communities and interactions, suitable to disentangle how land-use alteration impacts pollination ecology and its ecosystem service. Here, we used Maldives islands as model systems to investigate how pollinator richness, their mutualistic interactions with plants, and pollination efficiency are shaped by the degree of green area fragmentation (i.e., gardens, parks and semi-natural green covered patches), by considering both community- and species-level responses. To do this, we surveyed pollinators from 11 islands showing a gradient of green area fragmentation. In order to characterize the interactions between plants and pollinators and obtain a novel and comprehensive view of the key ecological dynamics, a DNA metabarcoding approach was adopted to identify the pollen carried by pollinators. We found that green area fragmentation at intermediate levels played positive effects on pollinator richness. However, fragmentation decreased interaction network complexity. Intriguingly, body size mediated the effect of landscape alteration on plant-pollinator interactions, as only the largest bee species expanded the foraging breath in terms of transported pollen richness at increasing fragmentation. In parallel, the pollination efficiency increased with pollinator species richness in two sentinel plants. This study shows that moderate landscape fragmentation of green areas shapes the ecosystem service of pollination, where in spite of interactions being less complex and mediated by pollinator body size, pollinator biodiversity and potential plant reproduction are supported.

Pollination efficiency of Apis mellifera (Hymenoptera: Apidae) on Solanum nigrum (Solanaceae) at Meskine (Maroua, Cameroon)

Most plant species require pollen transfer to produce fruits and set seeds. Although some insects visit flowers for nectar or pollen, not all flowering insects bring about pollination. To evaluate the impact of Apis mellifera Linnaeus on fruit and seed yields of Solanum nigrum Linnaeus, foraging and pollinating activities of worker bees were studied at Meskine in January 2019 and February 2020. The experiments were carried out on 540 flowers divided in four treatments: two treatments differentiated according to the presence or absence of protection of flowers regarding A. mellifera and other insect visits; the third with flowers protected and uncovered when they were opened, to allow A. mellifera visits and the fourth with flowers protected then uncorvered and reprotected without the visit of insects or any other organism. The foraging behaviour of A. mellifera on flowers, its efficiency pollination, the fruiting rate, the number of seeds per fruit and the percentage of normal seeds were evaluated. Results indicate that among 27 insect species recorded on flowers, A. mellifera ranked first accounting for for 34.16% of 2652 visits. This worker bee intensely harvested nectar and pollen. The mean foraging speed was 10.39 flowers / min. The mean abundance per 1000 flowers was 519.46. For the two years, throughout its pollination efficiency, A. mellifera increased the fruiting rate by 16.29%, as well as the percentage of normal seeds by 15.57%. Hence, the installation of honeybee colonies close to S. nigrum fields is recommended to improve fruit yields, seed quality, pollen as a hive product and honey production.

Metabarcoding Analysis of Pollen Species Foraged by Osmia excavata Alfken (Hymenoptera: Megachilidae) in China

To meet the pollination need of economic crops, Osmia excavata has been successfully used to improve the pollination efficiency of Rosaceae and Brassicaceae plants. As a widely used pollinator of economic crops, a systematic study of flower-visiting species and diversities of O. excavata stocked in China was not found. To investigate the foraging pollen species and diversities of O. excavata, beebread from 20 experimental plots in China was collected by the trap-nesting method and analyzed by DNA metabarcoding technology. A total of 26 pollen plants in 14 genera and nine families were identified. A further analysis showed that the richness and abundance of the wild flowering plants in orchards and farmlands were lower than those in the nearby semi-natural habitats. The favorite pollen comes from economic crops apple and rape and wild flowering plants Juncus interior, Rosa gymnocarpa, and Rosa laevigata. Through a diversity index analysis, it was found that the Anhui region has the highest pollen plant diversity, while the Liaoning region has the lowest. Our results can provide a basis for flower-visiting species and diversities of O. excavata.

Pollination Efficiency of Amegilla calens (Hymenoptera: Apidae) on Gossypium hirsutum L. (Malvaceae) Variety L457 Flowers at Meskine (Maroua, Cameroon)

This study was carried out to evaluate the impact of Amegilla calens bee on fruit and seed yields of G. hirsutum in an experimental field, in September 2018 and 2019. The experiments were carried out on 540 flowers divided in four treatments: 120 flowers accessible to all visitors; 120 flowers bagged to avoid all visits; 200 flowers protected and uncovered when they were opened, to allow A. calens visits; 100 flowers bagged then uncovered and rebagged without the visit of insects or any other organism. Bees daily rhythm of activity, its foraging behaviour on flowers, its pollination efficiency, the fruiting rate, the number of seeds per fruit and the percentage of normal seeds were evaluated. Results indicate that among 11 insect species recorded on flowers, X. olivacea ranked second and harvested nectar. Throughout the pollination efficiency of a single flower visit, X. olivacea provoked a significant increase of the podding rate, the mean number of seeds per pod, the percentage of normal seeds and the mean weight of a seed by 39.48 %, 18.19 %, 49.62 % and 31.53 % respectively. The conservation and installation of X. olivacea nests close to P. vulgaris fields is recommended to improve its pod production and seed quality.

Differences in Pollination Efficiency Among Three Bee Species in a Greenhouse and Their Effects on Yield and Fruit Quality of Northern Highbush ‘Bluecrop’ Blueberry

Different pollinators exhibit different adaptability to plants. Here, we compared the performance in visiting frequency and pollination efficiency among three bee pollinators (Bombus terrestris, Apis cerana, and Apis mellifera) on greenhouse-grown northern highbush ‘Bluecrop’ blueberry plants and evaluate their effects on yield and fruit quality. Our results indicated that the duration of daily flower-visiting of B. terrestris was 24 and 64 minutes longer than that of A. cerana and A. mellifera, respectively, and the visiting time of a single flower for B. terrestris was substantially shorter than the other two bee species, and pollen deposition on the stigma from single visit by B. terrestris was twice and three times that of A. cerana and A. mellifera, respectively. The yield of individual plants pollinated by B. terrestris showed an increase of 11.4% and 20.0% compared with the plants pollinated by A. cerana and A. mellifera, respectively, with the rate of Grade I fruit (>18 mm diameter) reaching 50.8%, compared with 32.9% and 22.5% for A. cerana and A. mellifera groups, respectively. Moreover, the early-to-midseason yield of plants pollinated by B. terrestris was higher, and the ripening time was 3 to 4 days earlier. An artificial pollination experiment demonstrated that seed set of high (≈300), medium (90–110), and low (20–30) pollination amounts were 43.0%, 42.5%, and 10.5%, respectively, and the corresponding mean weights of single fruits (related to the seed number inside) were 2.8, 2.7, and 1.2 g, respectively. The highly efficient pollination of B. terrestris was attributed to its behavior of buzz-pollination. Therefore, it is preferential for pollination of ‘Bluecrop’ blueberry in the greenhouse.

Effects of sexual dimorphism on pollinator behaviour in a dioecious species

Floral traits often display sexual dimorphism in insect-pollinated dioecious plant species, with male individuals typically being showier than females. While this strategy is theorized to be optimal when pollinators are abundant, it might represent a risk when they become scarce, because the disproportionately high number of visits on the most attractive sex, males, might preclude efficient pollen transfer from males to females. Here, the effect of sexual dimorphism on pollination efficiency was assessed in experimental arrays of dioecious Silene dioica that were exposed to one frequent visitor of the species, Bombus terrestris, and that differed in the magnitude of sexual dimorphism for either flower number or flower size. While flower size dimorphism did not impact pollination efficiency, we found that flower number dimorphism negatively affected the number of visits on female plants, on female flowers and on the number of female flowers visited after a male flower. However, flower number dimorphism had no effect on the number of pollen grains deposited per stigma, presumably because the decrease in the number of visits to female flowers was compensated by a higher number of pollen grains deposited per visit.