Newly hatched to one day-old flies were collected and transferred to
fresh food vials. The following day, they were starved as described
(see Starvation procedure). Four hours before the end of the
starvation period, female flies (if not stated otherwise) were
briefly immobilized by cold-anesthesia. Their head and thorax were
glued to a triangle-shaped copper hook (0.05 mm in diameter)
using a UV sensitive glue (3M ESPE, Sinfony Indirect Lab
Composite, Minneapolis, USA). Animals were then kept individually in
small chambers (14 mm in diameter x 28 mm in height,
custom-made) with ad libitum access to water until the test.