A "SPARC2-I" module separates 20XUAS regulatory sequences from sequence encoding a Drosophila codon-optimized version of GtACR1 that is tagged with EYFP. The SPARC2-I module comprises: a truncated attP site, a STOP cassette, a second attP site (full-length site) 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 EYFP-tagged GtACR1, while if the attP site downstream of the STOP cassette is utilized, the STOP cassette is preserved. Recombination of the attB site with the full-length attP downstream of the STOP cassette is more likely than recombination with the shortened attP site upstream of the STOP cassette, resulting in sparse expression of EYFP-tagged GtACR1 in the presence of phiC31:int approximately 15% of the time.