To determine if amino acids in the midgut lumen are sufficient to trigger RER whorl unwinding in midgut epithelial cells of Ae. aegypti mosquitoes, females were fed an artificial amino acid meal and dissected midguts were characterized for ultrastructural changes at the subcellular level using electron microscopy (EM). As seen in representative electron micrographs (Figure 1 ), large whorls of stacked RER membranes were observed in midgut epithelial cells from unfed (sugar only) mosquitoes, with some RER whorls containing .50 stacked membranes. The whorls appeared to consist entirely of tightly packed RER membranes, with no evidence of a core lipid droplet as seen in other organisms [25] . Quantitative measurements of whorl size in 20 randomly chosen EM fields revealed that the RER whorls ranged in size from ,5-35 mm 2 in unfed mosquitoes ( Figure 2 ). However, following a 30 minute amino acid feeding period, and another 30 minutes of recovery, midgut epithelial cells were found to contain significantly fewer RER whorls of .5 membrane stacks (p,0.001) ( Figure 2 ). Moreover, most of the RER contained in the midgut epithelial cells of amino acid fed mosquitoes was arranged in short linear stacks ( Figure 1C ). Quantitative measurements of RER whorl size and number in midgut epithelial cells following a recovery period of 120 minutes after amino acid feeding gave similar results, suggesting that RER whorl unwinding is rapid and complete by 30 minutes post feeding ( Figures 1D and 2 ).