Observing the Color Preferences of Native Pollinators

Introduction 

Pollinators play a crucial role in maintaining biodiversity and supporting the survival of numerous plant species. This diverse group includes bees, butterflies, moths, birds, bats, flies and beetles, each contributing to ecosystem health. Bees, for example, are responsible for pollinating approximately 75% of global crops, underscoring their importance in agricultural productivity.¹ Declines in pollinator populations can have far-reaching consequences for ecosystems and plant diversity.² Despite their significance, pollinators face threats such as habitat loss, pesticide use, climate change, invasive species and disease.³ The decline of pollinators presents a serious challenge, underscoring the need to understand their survival requirements.⁴ One key factor is their color preferences, which can offer valuable insights into enhancing plant-pollinator interactions.  

Research has shown that bees are attracted to saturated colors like blues and purples but struggle to perceive reds due to their lack of red receptors.² Instead, their color receptors are primarily ultraviolet (UV).² While studies on bee color preferences have provided valuable insights, there is a need to expand research to investigate the color and UV preferences of other native pollinators, addressing a critical gap in our understanding. 

Methods 

Data was collected at Sleeping Giant State Park located in Hamden, CT. White Shasta daisies were colored with both UV and regular pollinator safe paint: Blue, pink, purple, yellow and white (control). 

The Shasta daisies were placed at Sleeping Giant and were left for 30 minutes to allow them to acclimate to the environment, before observations began. Pollinators were observed and recorded based on the number and type of pollinators, the time spent on a flower and its color. 

To incorporate ultraviolet (UV) elements into the original methods, UV paints were tested to determine their UV reflectance values. Various UV paints were evaluated to identify those that would produce the most distinct results and work within this research. 

The data was quantified and presented in a graph (Fig. 5), which illustrates the comparison between non-UV and UV paints, highlighting the differences in color reflectance. 

Discussion 

The results of this study provided insights into the color preferences of native pollinators, particularly hymenopterans and dipterans, and their responses to ultraviolet and non-UV flowers. As hypothesized, color played a significant role in attracting pollinators with UV-reflecting flowers demonstrating a strong influence on both visitation time and the number of visits in many cases. 

The results for hymenopterans showed significant differences in visitation time and frequency between UV and non-UV flowers (Fig. 1). The extended visitation times on UV-blue flowers compared to other colors such as pink and yellow suggest that UV-reflecting flowers particularly those in blue hues may offer stronger visual cues that are more attractive to bees and wasps (Fig. 2). This finding aligns with previous research that shows bees are highly sensitive to UV light and prefer saturated colors, such as blue and purple, due to their enhanced visibility under UV reflection.² 

In contrast, the results for dipterans revealed no significant differences in visitation time between UV and non-UV flowers (Fig. 3). However, the number of visits by flies showed notable differences between UV and non-UV flowers, particularly for pink, purple and white UV-reflecting flowers (Fig. 4). This suggests that although UV reflection may not directly impact the duration flies spend on flowers, it can still influence their attraction to specific colors. These findings align with previous research indicating that fly species are attracted to UV light.⁶ It is important to note that when examining fly species more closely, hoverflies exhibited a significant difference in average visitation times. This is the first time UV floral preference has been documented in dipertans. 

Overall, these findings emphasize the critical role of UV light in shaping pollinator behavior. Understanding these preferences can help improve conservation efforts aimed at supporting native pollinator attraction. 

Future research should expand to include broader range of pollinators and investigate additional factors, such as scent and flower shape, which may also influence pollinator preferences. Additionally, further exploration of the physiological mechanisms underlying pollinator color vision, particularly in relation to UV sensitivity, could provide deeper insights into optimizing plant-pollinator dynamics in natural and agricultural settings.

References

¹ Ollerton, J., Winfree, R., & Tarrant, S. (2011). How many flowering plants are pollinated by animals? Oikos, 120(3), 321-326.
² Papiorek, S., Rohde, K., and Lunau, K. (2013). Bees’ subtle colour preferences: how bees respond to small changes in pigment concentration. Naturwissen schaften 100, 633–643. doi: 10.1007/s00114-013-1060-3
³ Potts, S. G., Biesmeijer, J. C., Kremen, C., Neumann, P., Schweiger, O., & Kunin, W. E. (2010). Global pollinator declines: trends, impacts and drivers. Trends in Ecology & Evolution, 25(6),
345-353.
⁴ Shrestha, M., Dyer, A. G., and Burd, M. (2013). Evaluating the spectral discrimination the evolution of flower colours. Commun. Integr. Biol. 6:e24000. doi: 10.4161/cib.24000
⁵ Winfree, R., Aguilar, R., Vázquez, D. P., LeBuhn, G., & Aizen, M. A. (2018). A meta-analysis of bees' responses to anthropogenic disturbance. Ecology Letters, 21(7), 962-970.
⁶Barghini, Alessandro & de Medeiros, Bruno. (2012). UV Radiation as an Attractor for Insects. LEUKOS The Journal of the Illuminating Engineering Society of North America. 9. 47-56. 10.1582/LEUKOS.2012.09.01.003.