The influence of light and the place of its perception on the flowering of Pharbitis nil.

The estimation of participation and density of forage species in several xerothermic communities of the Lublin Upland were carried out in 2004 and 2005. Most plants species visited by bees are grouped in plots of the Brachypodio-Teucrietum and the Adonido-Brachypodietum pinnati communities. The nectariferous and polleniferous taxons are mostly perennials predominated by hemicryptophytes (79%), others are terophytes and geophytes (21%). Successive blooming of the nectariferous and polleniferous species in both associations ensures unbroken food flow from the early spring until the late summer and early autumn. Xerothermic swards make a valuable food potential to be important for the Apoidea before and after blooming of the main forage cultivated crops