In this study, we describe a novel bacterial endosymbiont that uses a peculiar route of transmission in the scale insect Insignorthezia insignis. The bacteria accumulate outside developing oocytes, after which, the epithelial cells surrounding the oocyte undergo bizarre transformations. The cells typically have a cuboid or columnar morphology. However, upon contact with the bacteria, they lose their shape and instead transform into tubular elongations. Further examination revealed that these tubular protrusions are densely packed with the bacterial endosymbiont, which then detach from their cells to be incorporated inside the developing embryo. The cells thus functions as a transitory vehicle, transporting the bacteria from the exterior of the oocyte to its interior. Here, they synthesize essential nutrients such as amino acids and vitamins, which are required for optimal embryonic growth. Elimination of the bacteria from the embryos led to high insect mortality and severe developmental defects. The endosymbiont has a highly eroded genome – only 0.86 Mb. The bacterium has lost several of its genes while adapting to its endosymbiotic lifestyle. However, some genes encoding for nutrient-biosynthesis, which were missing from the endosymbiont’s genome were found to be present in the host genome, acquired horizontally from bacteria other than the endosymbiont. Thus, the study reports co-evolution between the genomes of the host and the symbiont.

Original publication: Ojaswini, Pal, S., Dhibar, A., Chandra, K., Rangarajan, A. and Shukla, S.P., 2026. Cellular remodeling of ovarian follicular epithelial cells transmits an obligate nutritional endosymbiont in a scale insect. Proceedings of the National Academy of Sciences, 123(16), p.e2532091123. https://doi.org/10.1073/pnas.2532091123

Photographs by Sourajyoti and Ojaswini