a Inhibition of actin polymerization with Latrunculin B did not affect expulsion of M. gaditana from infected larvae during 12 hours of live imaging, as would be expected from constitutive exocytosis. (n=3) b ERK5 inhibition with XMD17-109 significantly (p = 0.000013) reduced the fraction of symbiotic larvae when pre-treated for 1 hour and treated during a 24-hour infection (n=6) and c increased (p = 0.013) the percentage of symbionts expelled during 12 hours of live imaging (n=5). d Larvae with normal ERK5 activity were able to form a LAMP1-positive symbiosome, while larvae treated with the ERK5 inhibitor XMD17-109 showed massively reduced accumulation of LAMP1 when pre-treated for 1 hour and treated during a 5-hour infection. LAMP1 (magenta); nuclei (cyan); symbiont (white). Scale bar represents 10 μm. e ERK5 inhibition significantly (p = 0.0000027) reduced the fraction of symbionts with LAMP1 accumulation (n=3). In all graphs, error bars represent mean ± 95 % CI. Statistics are based on a two-sided generalized linear mixed model accounting for repeated measurements. Bars above graphs represent duration of infection (black dots), treatment (grey fill) and live imaging (where applicable). Bars above graphs represent duration of infection (black dots), treatment (grey fill) and live imaging (where applicable). *P < 0.05, **P < 0.01, ***P < 0.001.