Flower and Nectar Characteristics of Nine Species of Labiatae and their influence on Honeybee Visits

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Abstract
Summary The anatomy of the nectary, the relative amount of nectar secreted, the composition of the nectar and its sugar concentration, were studied in 9 species of the family, Labiatae (Coridothymus capitatus, Melissa officinalis, Phlomis viscosa, Rosmarinus officinalis, Salvia fruticosa, S. hierosolymitana, S. judaica, Satureja thymbra, Stachys aegyptiaca). The visitng rate of the honeybees to the various species was investigated. The nectar is secreted from the asymmetrically thick, disc-like nectary, through modified stomata. These occur on the thicker side of the nectary only. There is a correlation between the volume of the nectary and the amount of nectar secreted. The larger the nectary, the more nectar it secretes. No correlation was found between the type of vascular tissue (phloem, xylem) and the sugar concentration in the nectar, Rosmarinus officinalis and Coridothymus capitatus were the species most frequently visited by honeybees. The quantitative relationship between sucrose, glucose and fructose differed in the various species examined. Three groups of species were distinguished: 1. Melissa and Rosmarinus, in which the amount of hexoses was equal to that of sucrose; 2. Coridothymus, Salvia judaica and Stachys, in which the hexoses were dominant; 3. Phlomis, Salvia fruticosa and Satureja, in which sucrose was dominant. The concentration of the amino acids in the nectar was, in general, low. No clear correlation between the characteristics of the Sowers or of the nectar and the frequency of honeybee visits could be established.