Horizontal transfer of Wolbachia is clathrin mediated. (A) Uninfected Drosophila S2 cells were pretreated with 80 μM dynasore or DMSO (control) for 1 h prior to seeding Wolbachia-infected Drosophila JW18 cells in a transwell insert above them. After being cocultured for 1, 2, or 3 days, new Wolbachia infections in previously uninfected S2 cells were visualized by FISH in 3 to 7 fields of view for each group. Data are presented as proportion of infected cells ± SEM and were analyzed by t test to determine differences between control and dynasore-treated groups at each time point (t = 2.96, df = 6 at 1 day; t = 3.58, df = 4 at 2 days; t = 3.05, df = 6 at 3 days). Differences were deemed significant when the P value was <0.05 (indicated by an asterisk above the bracket). (B) Uninfected Drosophila S2 cells were pretreated with 10 μM chlorpromazine or DMSO (control) for 1 h prior to seeding Wolbachia-infected Drosophila JW18 cells in a transwell insert above them. After being cocultured for 1, 2, or 3 days, new Wolbachia infections in previously uninfected cells were visualized by FISH and analyzed as described for panel A (t = 5.73, df = 9 at 1 day; t = 2.44, df = 9 at 2 days; t = 2.51, df = 7 at 3 days).