Answers are grounded in this paper and cite their sources.
Ola Jennersten, Douglass H. Morse, The Quality of Pollination by Diurnal and Nocturnal Insects Visiting Common Milkweed, Asclepias syriaca, The American Midland Naturalist, Vol. 125, No. 1 (Jan., 1991), pp. 18-28
No takes yet. Share an insight, caveat, or question.
Jennersten et al. (1991) studied this question.
Synapse has enriched 10 related papers. Consider them for comparative context: