Wonder how they managed to measure such weak signals from the flowers. Also not sure if signal is the right term to use, because from the article it seems that no information (in conventional sense)is being transferred. Charged particle q (bumblebee) feels some force (F=q*E1 since we can neglect magnetic field) that is the consequence of static field E1 from flower :) Although it could also be the other way round, i.e. the bumblebee could produce field E2 etc.