I know that this seems like an odd question, but I notice that the hummingbirds and butterflies go to the same plants everyday, sometimes more than once a day, and that made me wonder how quickly the plants could create nectar. I don't study the hummers or butterflies closely enough to know which petals they eat from at each meal, but I do wonder if some of plants can make nectar faster than others. If there are any faster producers, I would add them to my garden.
penne, I don't know the answer to your question but I did find this abstract from a German botany study of bumblebee nectaring which indicates there are different rates of nectar replenishment in different varieties of flowers.
http://www.biology.qmul.ac.uk/research/staff/chittka/chittkalab/PDF/Nigel/RaineChittka_2007_EntGenShortComm.pdf
You know, I've often wondered the same thing. My porterweed gets hit up so often (by hummingbirds and butterflies) that I keep wondering how it can feed all those critters all day long.
Melanie
