The Srr coding region ( 3R:9365491..9367646 , FB2018_02) has been deleted and replaced by a "T2A-Flp-STOP" cassette containing the FLP coding sequence and a 3P3-RFP marker flanked by loxP sites. This results in FLP being expressed under the control of Srr regulatory sequences, with the Srr coding region knocked-out.