Key points are not available for this paper at this time.
Peter G. L. Klinkhamer, Tom J. de Jong, Effects of Plant Size, Plant Density and Sex Differential Nectar Reward on Pollinator Visitation in the Protandrous Echium vulgare (Boraginaceae), Oikos, Vol. 57, No. 3 (Apr., 1990), pp. 399-405
Klinkhamer et al. (Sun,) studied this question.