# Caught in the act: the invasion of a viral vector changes viral prevalence and titre in native honeybees and bumblebees

## TL;DR

A new study shows how a viral vector invasion in bees rapidly changed virus prevalence and affected both honeybees and bumblebees.

## Contribution

The study reveals how vector-mediated transmission can rapidly alter viral communities in bee populations.

## Key findings

- Deformed wing virus type B prevalence and titre increased drastically in honeybees after the varroa invasion.
- Slow bee paralysis virus appeared in both honeybees and bumblebees one year after the invasion.
- Black queen cell virus declined in honeybees following the varroa introduction.

## Abstract

Novel transmission routes change pathogen landscapes and may facilitate disease emergence. The varroa mite is a virus vector that switched to western honeybees at the beginning of the last century, leading to hive mortality, particularly in combination with RNA viruses. A recent invasion of varroa on the French island of Ushant introduced vector-mediated transmission to one of the last varroa-naive native honeybee populations and caused rapid changes in the honeybee viral community. These changes were characterized by a drastic increase in deformed wing virus type B prevalence and titre in honeybees, as well as knock-on effects in bumblebees, particularly in the year following the invasion. Slow bee paralysis virus also appeared in honeybees and bumblebees, with a 1 year delay, while black queen cell virus declined in honeybees. This study highlights the rapid and far-reaching effects of vector-borne transmission that can extend beyond the directly affected host species, and that the direction of the effect depends on the pathogen’s virulence.