Pollination: Plant flowers

Supporting evidence from individual studies

1. A replicated, randomized, controlled study in 2009 on an organic farm in Sonoma County, California, USA, found that honey bees Apis mellifera and wild bees preferred different flower species planted in flower strips surrounding kale plots, and this varied seasonally. Implementation options: From 24 June to 10 July, more honey bees were found on wild mustard Brassica sp. (11 visits/sample), compared to other species in peak bloom (0–5), but visits by wild bees did not differ significantly between these species (0.1–1.6). From 10 to 22 July, more honey bees were found on tansy phacelia Phacelia tanacetifolia (28 vs 0–4 visits/sample) and wild arugula Diplotaxis muralis (19 vs 0–4), and more wild bees were found on phacelia (5.4 vs 0–2.4), compared to other species in peak bloom. From 5 to 19 August, more honey bees were found on white borage Borago officinalis (33 vs 0–11 visits/sample), and more wild bees were found on phacelia (6.2 vs 0.1–2.0), compared to other species in peak bloom. From 9 to 23 September, more honey bees were found on borage (10 visits/sample), compared to other species in peak bloom (0–1), but visits by wild bees did not differ significantly between these species (1.0–2.5). Methods: Two rows of kale Brassica oleracea, between two strips (four rows) of one flower species, were planted on 16 May in each plot (3 x 6 m). There were five replicate plots for each of nine flower species. Invertebrates were sampled by counting flower visitors (6 minutes/plot, every 5–9 days) or vacuuming plants (15 seconds/plot, 25 x 50 cm area, every 12–15 days).

   Study and other actions tested

   Referenced paper

   Hogg B.N., Bugg R.L. & Daane K.M. (2011) Attractiveness of common insectary and harvestable floral resources to beneficial insects. Biological Control, 56, 76-84.

2. A replicated, controlled study in 2011 in an organic tomato field near Pisa, Italy, found that wild bees increased over time in some flower plots but decreased over time in others. Implementation options: In plots with three species from one plant family (Apiaceae), or six species from two plant families (Apiaceae and Fabaceae), numbers of bees increased over time (minimum: 0.3 bees/plot, 10–31 days after flowering; maximum: 3 bees/plot, 38–45 days after flowering). Similar numbers of bees were found in both of these flower-species mixtures (0.3–3 bees/plot). In plots with nine plant species (three Apiaceae, three Fabaceae, and three others), numbers of bees decreased over time (maximum: 3.7 bees/plot, on the first day of flowering; minimum: 0.2 bees/plot, 38 days after flowering). Methods: Four treatments were compared: three, six, or nine flower species/plot, and a control with no flowers. Five plots/treatment were sown with flower seeds on 6 and 21 June. Each flower plot (2 x 10 m) was next to a tomato plot (4 x 10 m). Bees on flowers were sampled with aspirators every 14 days after flowering began.

   Study and other actions tested

   Referenced paper

   Balzan M.V., Bocci G. & Moonen A. (2014) Augmenting flower trait diversity in wildflower strips to optimise the conservation of arthropod functional groups for multiple agroecosystem services. Journal of Insect Conservation, 18, 713-728.

3. A replicated study in 2009–2011 in farmland in the Central Valley, California, USA, found more bees and bee species on one species of flowering plant than on five other species. Implementation options: Gum plant Grindelia camporum attracted more individuals and species of native bees than did five other species of flowering plants (190–220 vs 0–60 individuals; 10–11 vs 1–6 species). Methods: At each of three sites, five plots were planted with mixtures of native forbs in October 2009. Plots were 3 x 15 m. Bees on flowers were netted once/month (20 minutes/sample, April–September 2010–2011).

   Study and other actions tested

   Referenced paper

   Wilkerson M.L., Ward K.L., Williams N.M., Ullmann K.S. & Young T.P. (2014) Diminishing returns from higher density restoration seedings suggest trade-offs in pollinator seed mixes. Restoration Ecology, 22, 782-789.

4. A replicated, controlled study in 2013 in coriander plots near Madrid, Spain, found more pollinators on coriander flowers next to planted flower strips than on coriander flowers next to unplanted field margins. Crop visitation: More pollinators (bees, beetles, and syrphid flies) were found on coriander flowers next to flower strips than on coriander flowers next to unplanted margins (1.2–1.6 vs 0.2 pollinators/minute). Implementation options: Similar numbers of pollinators were found on coriander flowers next to flower strips with one flower species, compared to six (1.2 vs 1.6 pollinators/minute). More pollinators were found in flower strips with one flower species, compared to six (1.6 vs 0.4 pollinators/minute). Methods: Potted coriander plants were transplanted into the field on 1 May 2013, one month before flowering. Fifteen pots were buried 1.5 m from three field margins with one flower species (Diplotaxis tenuifolia), three margins with six flower species, or three unplanted margins (135 pots total). All margins were 1.5 x 15 m. Flowers were planted in autumn 2012. Pollinators were observed twice/week (3–21 June, 12 minutes/field, nine minutes/field margin), and were counted only if they touched the reproductive parts of flowers.

   Study and other actions tested

   Referenced paper

   Barbir J., Badenes-Pérez F.R., Fernández-Quintanilla C. & Dorado J. (2015) Can floral field margins improve pollination and seed production in coriander Coriandrum sativum L. (Apiaceae)? Agricultural and Forest Entomology, 17, 302-308.

5. A replicated, randomized study in 2011–2012 in a barley field near Madrid, Spain, found different numbers of flower visitors on different species and mixtures of planted flowers. Implementation options: The highest number of bees were found on Coriandrum sativum in 2012 (1.7 visits/minute) and the lowest number were found on Antirrhinum majus in 2011 (0 visits/minute). The highest number of syrphid flies were found on Lobelia maritima in 2011 (0.9 visits/minute) and the lowest number in 2011 were found on A. majus (0 visits/minute; approximately 0 visits/minute were also seen on all flowers in 2012). The highest number of beetles were found on Echium plantagineum in 2011 (1.2 visits/minute) and the lowest number were found A. majus and Allium schoenoprasum in 2011 (0 visits/minute). Plots with six or seven flower species did not consistently have more or fewer flower visitors than plots with one flower species. Methods: For each treatment (2011: 12 one-species and 2 six-species plantings; 2012: 7 one-species and 1 seven-species plantings), there were three plots (1.3 x 1.3 m). Flower visitors were counted (twice/week, nine minutes/plot) only if they touched the reproductive parts of flowers.

   Study and other actions tested

   Referenced paper

   Barbir J., Badenes-Pérez F.R., Fernández-Quintanilla C. & Dorado J. (2015) The attractiveness of flowering herbaceous plants to bees (Hymenoptera: Apoidea) and hoverflies (Diptera: Syrphidae) in agro-ecosystems of central Spain. Agricultural and Forest Entomology, 17, 20-28.

6. A replicated, controlled study in 2010–2011 in farmland in the Central Valley, California, USA, found more wild bees and bee species in perennial flower plantings, compared to annual flower plantings or unplanted controls, and more wild bees in species-rich but not species-poor annual plantings, compared to unplanted controls. Pollinator numbers: More wild bees were found in perennial flower plantings, compared to unplanted plots (525–775 vs 75–100 individuals). More wild bees were found in ten-species annual plots, compared to unplanted plots (175–250 vs 75–100 individuals), but no difference was found between five-species annual plots and unplanted plots (100–175 vs 75–100). More bee species were found in perennial plots, compared to unplanted plots (17–21 vs 8–13 bee species), but not in annual plots, compared to unplanted plots (10–15 vs 8–13). More honey bees Apis mellifera were found on annual or mixed compared to unplanted plots (450–750 vs 25–75 individuals). More honey bees were found on perennial compared to unplanted plots in 2011 (650 vs 25 individuals) but not in 2010 (250 vs 75). More bumblebees Bombus spp. were found on annual or perennial compared to unplanted plots (5–50 vs 0 individuals), and mixed plots (5–25) were not significantly different from annual, perennial, or unplanted plots. Similar numbers of syrphid flies were found in different plots (5–40 individuals). Implementation options: More wild bees were found in perennial flower plots, compared to annual (525–775 vs 100–225 individuals), but not compared to mixed plots with annuals and perennials (525–775 vs 525–650). More bee species were found in eight-species perennial plots, compared to five- or ten-species annual plots (20–21 vs 10–15 bee species), and in five-species perennial plots, compared to five-species annual plots (17 vs 10–12), but not in five-species perennial plots, compared to ten-species annual plots (17 vs 12–15), or in perennial compared to mixed plots (17–21 vs 18–21). Methods: Six flower plots (ten-species annual, five-species annual, eight-species perennial, five-species perennial, mixed, and control) were planted on each of three sites. Plots were 3 x 15 m. Flower visitors were counted if they touched the reproductive parts of flowers (20 minutes/sample, six samples/plot).

   Study and other actions tested

   Referenced paper

   Williams N.M., Ward K.L., Pope N., Isaacs R., Wilson J., May E.A., Ellis J., Daniels J., Pence A., Ullmann K. & Peters J. (2015) Native wildflower plantings support wild bee abundance and diversity in agricultural landscapes across the United States. Ecological Applications, 25, 2119-2131.

7. A replicated, randomized study in 2011–2012 in an organic tomato field near Pisa, Italy, found similar numbers of wild bees in planted flower strips with different numbers of flower species, in most comparisons. Implementation options: More wild bees were found in flower strips planted with nine plant species, compared to three or six species, in 2012, but similar numbers were found in other comparisons (numbers of individuals not reported). Methods: Three treatments were compared: three flower species/strip (Apiaceae species), six species/strip (three Apiaceae and three Fabaceae), and nine species/strip (three Apiaceae, three Fabaceae, and three others). Three strips/treatment were sown with flower seeds (2011: 6 and 21 June; 2012: 13 and 17 June). Each flower strip (2 x 4 m) was positioned between two tomato plots (4 x 10 m/plot). Bees on flowers were sampled with aspirators every 14 days, after flowering began.

   Study and other actions tested

   Referenced paper

   Balzan M.V., Bocci G. & Moonen A. (2016) Utilisation of plant functional diversity in wildflower strips for the delivery of multiple agroecosystem services. Entomologia Experimentalis et Applicata, 158, 304-319.

8. A replicated, randomized study in 2012–2013 in a barley field near Madrid, Spain, found different numbers of pollinators on different species and mixtures of planted flowers. Implementation options: The highest number of pollinators were found on Nepeta tuberosa in 2011 (0.95 visits/minute) and the lowest number were found on Salvia verbenaca in 2011 (0 visits/minute). More pollinators were found in some plots with one flower species (N. tuberosa: 0.85–0.95 visits/minute; Hyssopus officinalis: 0.65–0.75) than in plots with six flower species (0.20–0.30 visits/minute), in both years (2012–2013). However, most of the other one-species plots were no different than the six-species plots (0.15–0.40 visits/minute). Methods: For each treatment (6 one-species and 2 six-species plantings), there were three plots (2.4 x 2.4 m), which were planted with three-month-old Lamiaceae seedlings in February 2011. Pollinators were counted (nine minutes/plot, once/week) only if they touched the reproductive parts of flowers.

   Study and other actions tested

   Referenced paper

   Barbir J., Azpiazu C., Badenes-Pérez F.R., Fernández-Quintanilla C. & Dorado J. (2016) Functionality of selected aromatic Lamiaceae in attracting pollinators in central Spain. Journal of Economic Entomology, 109, 529-536.