Ipomoea alba L.
This species may have a specific pollinator, most likely a moth with a tongue as long as the flower's tube.
As Danial F. Austin recently wrote when he identified this species: "...the flowers are pollinated by sphingid moths. I have no idea what visits them in Peru, but in FL they are visited by Tomato-hornworm (Manduca quinquemaculata), other species of Manduca, and Potato-hornworm moths (Agrius cingulata). The pond-apple or Giant Sphinx Moth (Cocytius antaeus). In short, by a series of moths with tongues long enough -- and even those whose tongues are too short recognize it as a potential source and visit the flowers." 14 August 2010