UAS regulatory sequences drive expression of Ilp2, in which a tag cassette comprised of Tag:MYC and FAP(L5-MG.L91S.E52D) has been inserted into the C-peptide part of the Ilp2 coding sequence. The protein produced can be used to report dense-core vesicle fusion pore openings when expressed at synapses; extracellularly applied membrane-impermeant malachite green (MG) derivatives can permeate the fusion pore, where they can be bound by FAP(L5-MG.L91S.E52D) homodimers, inducing far-red fluorescence of the MG derivative.