Biochemical studies have shown that in addition to globin, albumin, and immunoglobulin proteins, which make up 80% of the soluble proteins in human blood, free amino acids are also present in blood [21] . Based on physiological studies showing that artificial amino acids meals are sufficient to induce early events in the blood digestion process [33] , it has been proposed that amino acids could play a signaling role by inducing protease expression [24] . Consistent with this idea, we have recently shown that amino acid feeding stimulates translation of pre-existing early trypsin mRNA through activation of the TOR signaling pathway [23] . Since large ER whorl structures have been shown to exist in the midgut of Ae. aegypti and other mosquito species [2,3,4,5,6,8,9], we used EM ultrastructural analysis to test if amino acid feeding induces ER whorl unwinding. As shown in Figures 1 and 2 , our data clearly demonstrate that amino acid feeding does induce ER whorl unwinding, and moreover, that the most abundant whorls consist of rough ER membranes based on the high density of ribosomal particles.