Insulin-responsiveness as a function of food content and age. (A) Flies expressing the tGPH reporter construct were raised for ten days on food with differing sucrose content (top panels) or differing yeast extract content (lower panels), starved overnight and re-fed. Starved flies show almost no plasma membrane staining, except flies fed 5% and 10% yeast food. Re-feeding flies raised on low nutrient food leads to strong plasma membrane staining, while flies raised on high nutrient food do not respond. (B) Older flies raised on 5% sucrose food do not respond to sucrose re-feeding with plasma membrane staining, while flies raised on 5% yeast food retain residual IIS activity (blue: DAPI; green: GFP; yellow arrows depict tGPH staining in the plasma membrane, yellow triangles depict weak plasma membrane staining).