a–c, Stage-6 cellular blastoderm C. floridanus embryos with DAPI in white from wild-type colonies (n ≥ 30 embryos) (a), colonies treated with ampicillin (n ≥ 15 embryos) (b) or colonies treated with rifampicin (n ≥ 15 embryos) (c). d–o, C. floridanus embryos stained for nos mRNA (d–f, j–o) and osk mRNA (g–i) in blue collected from wild-type colonies (n ≥ 30 embryos each) (d, g, j, m), colonies treated with ampicillin (n ≥ 15 embryos each) (e, h, k, n) or colonies treated with rifampicin (n ≥ 15 embryos each) (f, i, l, o). p, q, Stage-12 mild-phenotype embryos collected from rifampicin-treated C.-floridanus colonies, showing expression of the segment polarity gene en in blue (n ≥ 15 embryos) (p) or abdA mRNA in blue (n ≥ 15 embryos) (q). r, s, Lasius niger embryos collected from rifampicin-treated colonies showing nos mRNA in blue in stage-6 embryos with normal primordial germ cells (pgc) (n ≥ 5 embryos) (r) and stage-12 embryos with normal germ cells (gc) (n ≥ 5 embryos) (s). Segments marked are as following: maxillary (mx), thoracic segments 1–3 (t1–t3) and abdominal segments 1–10 (a1–a10). White arrowheads indicate presence of Blochmannia (bl). White and black asterisks in embryos from rifampicin-treated colonies indicate loss of Blochmannia or loss of germline gene expression. d–i, Black arrowheads indicate zones. j–l, Black arrowheads indicate germline capsule(s) (cp). m–o, Black arrows indicate normal bacteriocyte (bc) and gonads (gc), development. Anterior is to the left, dorsal is to the top (a–f, p-r); dorsal is towards the reader in g–i, m–o, s; and ventral is towards the reader in j–l. In situ hybridization experiments were repeated at least 8 times (C. floridanus) or 4 times (L. niger) independently.