# Bee swimming is adaptive but disrupted by insecticide

## TL;DR

Honey bees can swim on water surfaces, a behavior that helps them escape, but this is disrupted by insecticides and may have evolved before social living.

## Contribution

The study reveals that skototaxis in bees is adaptive and evolutionarily ancient, but is impaired by neonicotinoid insecticides.

## Key findings

- Honey bees exhibit skototaxis while swimming, aiding in reaching land.
- Thiamethoxam insecticide disrupts skototaxis by impairing motor control.
- Mason bees show stronger skototaxis than honey bees, with females swimming more efficiently.

## Abstract

A unique type of locomotion was recently discovered that honey bees (Apis mellifera L.) could propel their own body on water surface by keeping their upper wing surface dry while moving their wings. However, it was not clear whether such locomotive behavior was ecologically meaningful. Here we show that honey bees preferred a dark region (skototaxis) while hydrofoiling on the water surface in trying to reach the edge. However, this skototaxis was disrupted by a neonicotinoid insecticide thiamethoxam, via reducing the honey bees’ motor control. Finally, we show that mason bees (Osmia excavata) also displayed skototaxis, showing a significantly stronger preference for dark than honey bees. The female mason bees exhibited higher efficiency than males in swimming, as indicated by their shorter durations and distances. These findings suggest that swimming behavior in bees evolved before sociality and serves important adaptive and ecological functions. However, environmental pollution from excessive pesticide use may negatively impact this behavior.

Honey bees showed skototaxis while swimming to land quickly, thus it is most likely an adaptive trait. However, this behavior was shown to be disrupted by an insecticide. Skototaxis may have evolved before eusociality because a solitary bee species showed a stronger strength of this trait.