In infected larvae, the peritrophic membrane helps to retain the bacterial mass in the midgut lumen although P. larvae is able to penetrate this protective layer (Davidson, 1970; Yue et al., 2008) and to attack the epithelium at a later stage of the infection when the larval gut is massively filled with these pathogenic bacteria. Breaching of the epithelium occurs via the paracellular route, i.e. the cells move through the paracellular space to enter the hemocoel where they also live (migrate and proliferate) in the paracellular space