Bee pollination of Lathyrus odoratus (Fabaceae): Preferences based on patch density, average flower size, and flower color.

Abstract

Lathyrus odoratus (Fabaceae) are bee pollinated plants and must have characteristics with which to attract bees to their flowers. The purpose of this study was to see if certain plot level floral characteristics will attract more bees than others. We hypothesized that bees would be attracted to denser patches of flowering stems because of optimal foraging theory; bees can move between stems quickly and gather food at a higher rate because they do not waste energy traveling between patches. We also hypothesized that bees would be more attracted to plots with larger average banner heights and corolla lengths. Larger banner heights on flowers would be easier for bees to find, and longer corolla length may confer larger amount of pollen produced. A third hypothesis is that bees would prefer plots with lower proportions of pink flowers. We predict this because pink flowers would contrast less with the green foliage background than mixed or white flowers and be easier to locate. Finally, we hypothesize that bees will visit ultraviolet treated stems more than non-ultraviolet treated stems. We predict that they will see treated stems easier and therefore visit them more often. We observed 10 2m x 2m plots of sweet pea plants for one hour each in various pea plant patches. We measured average banner height, corolla length, number of stems, and color of stems in each plot. For the ultraviolet treatment we observed 7 1m x 1m plots within the same patch for 3.5 total observation hours. Half of the stems in each plot were ultraviolet paint treated. For both studies we recorded number of bee visits and lengths of bee visits. Total time of bee visitation did increase with increasing stem density of patches (R2 = 0.504, F ratio = 8.114, df = 8, p<0.05). Total time of bee visitation did not increase with larger banner heights or longer corolla lengths (R2 = 0.002, F ratio = 0.015, df = 8, p>0.05, R2 = 0.091, F ratio = 0.805, df = 8, p>0.05). Total time of bee visitation did not increase with decreasing proportions of pink flowers (R2=0.107, F ratio = 0.961, df = 8, p>0.05). Increasing ultraviolet reflectance did not increase mean bee stay length on stems (t = 1.871, df = 3, p>0.05). We measured average plot heights and average plot light levels and found no affect on amount of bee visitation. Pollinator visitation rates are important because pollination of plants is an essential process maintaining species diversity and production of agricultural crops.