Some Citrus Flower Characteristics and Honey Bee Preference

Abstract

Pollination by honey bees (Apis mellifera) is important to production of most hybrid citrus cultivars grown in Florida as they require cross-pollination to set commercial crops of fruit. However, bees often appear to prefer other cultivars than those requiring cross-pollination. Poor fruit set of a relatively new cultivar, ‘Ambersweet’, increased awareness of the problems associated with bee requirements and activity. To investigate these problems during flowering in 1997 and 1998, bee visits to flowers were determined in a round white mesh cage to evaluate bee preference for citrus flowers of different cultivars. Bee behavior in the cage appeared to approximate natural bee activity with flights tapering off by noon. The large-flowered cultivars ‘Valencia’ and ‘Hamlin’ orange and ‘Orlando’ tangelo were preferred over large-flowered ‘Ambersweet’. Large-flowered ‘Orlando’ and ‘Minneola’ tangelos were preferred over small-flowered hybrids, such as ‘Dancy’, ‘Robinson’, and ‘Murcott’, which had the lowest bee preference. Flower nectar volume and sugar concentration were measured in the springs of 1997–99 in commercial and research blocks of several citrus cultivars throughout central Florida. In 1998, more large-flowered cultivars had their highest nectar content and most of the cultivars had their highest sugar concentrations of the 3 years tested. Large-flowered cultivars of oranges and grapefruit produced more nectar per flower (9 to 21 µL/flower), but the sugar concentrations often were slightly lower (sometimes significantly) than in small-flowered mandarin hybrid cultivars. Large-flowered hybrid cultivars were usually intermediate in nectar production (4.3 to 10.5 µL) and low to intermediate in sugar concentration compared to other cultivars. Small-flowered mandarin hybrids had the lowest nectar volumes (2.1 to 3.3 µL). Flower volatiles were measured and some cultivar differences were found, most notably high limonene content in grapefruit, and four major compounds, pinene, myrcene, limonene, and linalool, were low in ‘Ambersweet’ and ‘Robinson’. Average nectar volumes per flower, which were highest in large-flowered non-hybrid cultivars, appeared to relate best to observed bee preference compared to sugar concentration and flower volatiles.