Flies were raised on cornmeal-yeast-glucose-agar medium under a 12/12 h light/dark cycle (lights on at 06:00 hrs) at 25°C. Newly hatched to one day old flies were collected and transferred into a vial containing Kimwipe paper soaked with 100 mM glucose for one to two days as previously described Zhang 2010. Starved flies were kept in a vial containing Kimwipe paper soaked with Evian® water for 20 h before testing.