20XUAS regulatory sequences are separated from sequence encoding lexA::p65 by a "SPARC-D" module that comprises: a full-length attP site of 60bp, a STOP cassette, a second attP site (60bp, full-length site), a spacer and an attB site. phiC31:int catalyzes irreversible recombination between the attB site and one of the two attP sites; if the attP site upstream of the STOP cassette is utilized, the STOP cassette is excised, permitting expression of lexA::p65, while if the attP site downstream of the STOP cassette is utilized, only the spacer is removed, and the STOP cassette is preserved. The "SPARC-D" module typically results in expression of the effector (in this case lexA::p65) in approximately 45% of cells.