The self-incompatible flowers of Linaria vulgaris have developed a range of mechanisms for attraction of insect visitors/pollinators and deterrence of ineffective pollinators and herbivores. These adaptive traits include the flower size and symmetry, the presence of a spur as a “secondary nectar presenter,” olfactory (secondary metabolites) and sensual (scent, flower color, nectar guide—contrasting palate) signals, and floral rewards, i.e. pollen and nectar. Histochemical tests revealed that the floral glandular trichomes produced essential oils and flavonoids, and pollen grains contained flavonoids, terpenoids, and steroids, which play a role of olfactory attractants/repellents. The nectary gland is disc-shaped and located at the base of the ovary. Nectar is secreted through numerous modified stomata. Nectar secretion began in the bud stage and lasted to the end of anthesis. The amount of produced nectar depended on the flower age and ranged from 0.21 to 3.95 mg/flower (mean = 1.51 mg). The concentration of sugars in the nectar reached up to 57.0%. Both the nectar amount and sugar concentration demonstrated a significant year and population effect. Pollen production was variable between the years of the study. On average, a single flower of L. vulgaris produced 0.31 mg of pollen. The spectrum of insect visitors in the flowers of L. vulgaris differed significantly between populations. In the urban site, Bombus terrestris and Apis mellifera were the most common visitors, while a considerable number of visits of wasps and syrphid flies were noted in the rural site.

Honey contains natural biologically active compounds, and its preventive and healing properties are primarily linked to its antioxidant activity. The antioxidant properties of honey can be related to the botanical origin and content of phenolic compounds. We tested 84 honey samples from Poland, representing eight honey varieties: acacia, phacelia, buckwheat, linden, rapeseed, heather, goldenrod, and honeydew. High-performance liquid chromatography with photodiode-array detection (HPLC-DAD) was used to determine the phenolic compound composition of honey extracts. Total phenolic compounds (TPC) and DPPH radical-scavenging activity were also evaluated. We detected vanillin aldehyde, vanillic acid, caffeic acid, p-coumaric acid, and trans-ferulic acid, as well as flavonoid pinocembrin, in all honey varieties. The results of our study showed that honeys with high antioxidant activity were characterized by significantly higher total phenolic compounds content. Neither clustering method nor principal component analysis (PCA) showed clear separation of each honey variety, possibly due to high intra-variety diversities. We suppose that the variability of qualitative and quantitative phenolic compound composition within honey varieties may result from the region of origin, secondary nectar sources, and the time of harvest.

In Europe, honey bees and bumble bees are among the most important pollinators, and there is a growing interest in understanding the effects of floral resource availability on their survival. Yet, to date, data on nectar and pollen supplies available to bees in agricultural landscapes are still scarce. In this paper, we quantify species-, habitat- and landscape-scale pollen production in the Lublin Upland, SE Poland. The production per unit area was highest (mean = 2.2-2.6 g/m²) in non-forest woody vegetation, field margins and fallows, whilst significantly lower pollen amounts were shown to be available in road verges and railway embankments (mean = 1.3-1.6 g/m²). At landscape scale, natural and semi-natural areas (forests and meadows/pastures) offered ca. 44% of the total pollen resources during the year. Relatively high amounts of pollen (ca. 35% of the year-round total pollen resources) were from winter rape, but this resource was short-term. Man-made, non-cropped habitats added only ca. 18% of the total pollen mass offered for pollinators during flowering season. However, they provided 66-99% of pollen resources available from July to October. There exists an imbalance in the availability of pollen resources throughout the year. Hence, a diversity of natural, semi-natural and man-made, non-cropped areas is required to support the seasonal continuity of pollen resources for pollinators in an agricultural landscape. Efforts should be made to secure habitat heterogeneity to enhance the flower diversity and continual pollen availability for pollinators.

The knowledge of nectar secretion and pollen production is important for understanding the biology of invasive species. In the present paper, the floral reward in Solidago canadensis and S. gigantea (Asteraceae), two invasive plant species in Europe, were investigated. Flowers of Solidago species are protandrous. The floral nectar was found to be rich in hexose (sucrose/fructose/glucose – 13.8/32.7/53.5% in S. canadensis and 18.3/35.1/46.6% in S. gigantea). The per-flower rewards (sugars/pollen) in the Solidago species were not abundant; however, due to the formation of dense populations and massive floral display, high amounts of resources were produced at the community level. The mean sugar output was 482.3 kg/ha in S. canadensis and 121.6 kg/ha in S. gigantea. The mean pollen yield was 30.7 kg/ha (S. canadensis) and 6.5 kg/ha (S. gigantea). In the landscape with limited floral resources, the nectar and pollen available in Solidago flowers are important and can provide additional (or even exclusive) food resources for pollinators during summer/late summer. In particular, areas invaded by Solidago species may be attractive to beekeepers, as >80.0% of visits were performed by Apis mellifera. However, a broad spectrum of wild insect visitors (including Bombus spp., Vespula spp., Diptera, Lepidoptera, Coleoptera) deserves further studies to assess the impact of mass flowering in Solidago species on the native plant species-insect interactions.