# Facultative Endosymbiont Serratia symbiotica Provides Fitness Benefits for Celery Aphid Semiaphis heraclei Collected from Plant Cnidium monnieri

## TL;DR

This study shows how the endosymbiont Serratia symbiotica affects the fitness of celery aphids depending on the host plant they come from.

## Contribution

The first investigation into the infection status and role of facultative endosymbionts in Semiaphis heraclei.

## Key findings

- Aphids collected from Cnidium monnieri showed improved fitness when infected with Serratia symbiotica.
- Serratia symbiotica had negative effects on aphids from Apium graveolens, reducing their reproductive rates.
- Infection rates of Spiroplasma and Rickettsia varied depending on the host plant.

## Abstract

Semiaphis heraclei Takahashi (Hemiptera: Aphididae) serves as a vital resource for natural enemies from functional plant Cnidium monnieri (L.) Cusson (Apiaceae), playing a crucial role in ecological dynamics. Endosymbionts influence the performance of their hosts. Here, we determined the communities of facultative endosymbionts in aphids from Lonicera japonica Thunb. (Caprifoliaceae), Apium graveolens L. (Apiaceae), and C. monnieri and assessed the performance of four aphid clones. The infection rates of Serratia symbiotica Moran (Gammaproteobacteria: Enterobacteriaceae) and Regiella insecticola Moran (Enterobacteriales: Enterobacteriaceae) reached 100%. Notably, the infection rates of Spiroplasma and Rickettsia varied across host plants. Fitness assessment revealed that aphids performed better on their natal hosts, exhibiting shorter nymphal development times and higher fecundity. S. symbiotica had contrasting effects on aphids based on their origin. It prolonged the development duration and decreased the intrinsic rate of increase (rm), net reproductive rate (R0), and finite rate of increase (λ) in aphids collected from plant A. graveolens. However, for aphids collected from plant C. monnieri, it shortened the doubling time (DT) and improved rm, R0, and λ, while prolonging the mean generation time. Our studies are the first to investigate the infection status and role of facultative endosymbionts in aphid S. heraclei, extending the documented effects of plant diversity to fluctuations in the infection rate, with potentially far-reaching consequences for related endosymbionts’ ecosystem processes.