Advertisement, flower longevity, reward and nectar protection in Labiatae.

Floral parameters were measured in 13 species of Labiatae in Israel, all of which are pollinated primarily by solitary bees. Nectar concentrations ranged from 17.3 to 60.2 per cent sucrose equivalents while nectar production varied from 0.35 to 18.2 μl per 24 hours. The floral reward, calculated as the energy content per flower, varied from 1.06 to 187.9 Joules. Floral advertisement was calculated as the floral planar projection (0.16–1.7 cm2). The length of the floral tube (4.3 – 21.3 mm) determines a bee's access to nectar and was used as a criterion for reward protection. Flower life span was observed under field conditions (3.1–6.3 days).
The nectar energetic value (Joules/flower) was significantly and positively correlated with: planar projection (r = 0.7889; P < 0.00001), tube length (r = 0.815; P < 0.0007), and with the floral longevity (r = 0.823, P < 0.0005). There were also significant positive correlations among all these parameters.

Therefore, larger flowers with bigger advertisement (= the planar én-face projection) offer more calorific reward per flower, and last for longer duration. Consequently, large rewards are better protected, both from short-tongued visitors as well as from climatic conditions.