Co-culturing S2 or C6/36 cells with PIP producing BHK cells increases infection efficiency. 1 × 106 S2 or C6/36 cells were added to BHK cells co-transfected with pBG78 and pBG44 24 hrs post-transfection. Co-cultures were incubated for 24 hrs and the S2 or C6/36 cells were removed by gentle washing and transferred to new plates. GFP fluorescence was detected 24 hrs later (Panels A2 and A4) and 10 ug/ml added. B. Cells were incubated for 5 days in the presence of blasticidin and phase contrast micrographs obtained to assess cell viability.