# Non‐Canonical, Somatic‐Dependent Vertical Transmission of Wolbachia in an Aphid

## TL;DR

This study reveals a new way Wolbachia bacteria are passed from mother to offspring in cedar bark aphids, using a 'piggybacking' strategy on other symbionts.

## Contribution

The paper identifies a novel somatic-dependent vertical transmission mechanism of Wolbachia in viviparous aphids.

## Key findings

- Wolbachia in Cinara cedri is primarily found in maternal and embryonic bacteriocytes, not germline cells.
- Wolbachia transmission occurs via a 'piggybacking' strategy on obligate symbiont transfer pathways.
- This transmission mode contrasts with the typical germline-based vertical transmission in other species.

## Abstract

Wolbachia, a widespread endosymbiotic bacterium that infects a broad range of arthropods and nematodes, relies on vertical transmission from mother to offspring. This process often involves colonisation of the host germline, subsequent transfer to developing oocytes, and utilisation of host yolk protein transport mechanisms such as vitellogenin uptake. However, the transmission strategies employed by Wolbachia in viviparous insects such as aphids are poorly understood. Here, we demonstrate a non‐canonical Wolbachia transmission mode in the cedar bark aphid Cinara cedri: the somatic‐dependent vertical transmission. After confirming consistent Wolbachia infection in C. cedri, we visualised the localization of Wolbachia, along with the obligate symbionts
Buchnera aphidicola
and
Serratia symbiotica
. Consistent with previous reports, Wolbachia in C. cedri were predominantly observed within maternal and embryonic bacteriocytes, the specialised cells housing obligate symbionts. Notably, Wolbachia cells were rarely detected in germline cells or early‐stage embryos and were directly transmitted from maternal bacteriocytes to developing embryos, coinciding with obligate symbiont transfer. These results suggest that Wolbachia in C. cedri has evolved a unique “piggybacking” strategy, utilising the obligate symbiont transmission system. Our study highlights the diversity of endosymbiont maternal transmission strategies and provides new insights into the underlying molecular mechanisms of action.

We discovered a novel somatic‐associated Wolbachia transmission strategy in cedar bark aphids (Cinara cedri), contrasting with its typical maternal vertical transmission. This unique maternally retained somatic re‐acquisition strategy—a “piggybacking” on the highly efficient obligate symbiont transmission pathway—reveals diverse endosymbiont strategies and offers insights into underlying mechanisms.