The countercurrent flow was monitored using the amaranth injection assay in wild-type flies and aquaporin knockdown flies (c724-Gal4>uas-Prip IRandc724-Gal4>uas-Drip IR) either unchallenged or collected 2 hpi. UC, unchallenged. An asterisk (*) indicates midgut-hindgut junction where the MpT are connected. Red arrow indicates accumulation of amaranth dye.
