# A Hitchhiker’s Ride: The Honey Bee Louse Braula Coeca (Diptera: Braulidae) Selects its Host by Eavesdropping

## TL;DR

Braula coeca, a bee louse, chooses its host by detecting specific pheromones from honey bees, helping it find bees more likely to be fed by others.

## Contribution

This study identifies specific pheromonal cues used by Braula coeca for host selection in African honey bees.

## Key findings

- Braula coeca prefers mandibular gland pheromones from bees carrying them over those without.
- Workers with Braula coeca have higher levels of queen and worker substances in their pheromones.
- Braula coeca shows a dose response to the queen substance, indicating its role in host selection.

## Abstract

The bee louse Braula spp. had until recently a distribution coincident with its host the honey bee. The adult fly usually attaches to a worker honey bee and steals food from its mouth. However, not all worker bees carry Braula spp. and the mechanism used by Braula spp. to select hosts is not well understood. Using choice remounting bioassays and chemical analyses, we determined host selection and the cues used by B. coeca, a species associated with the African honey bee Apis mellifera scutellata. Braula coeca successfully remounted bees from which they were initially removed and preferred their mandibular gland pheromones (MDG) over those of bees not carrying them. The bee lice did not show any preference for the cuticular hydrocarbons of both types of workers. Chemical analyses of the MDG extracts, revealed quantitative differences between the two categories of workers, with workers carrying B. coeca having more of the queen substance (9-oxo-2(E)-decenoic acid) and worker substance (10-hydroxy-2(E)-decenoic). Braula coeca showed a dose response to the queen substance, indicating its ability to use host derived kairomones as cues that allowed it to benefit from trophallactic dominance by individuals that have a higher probability of being fed by other workers.

The online version contains supplementary material available at 10.1007/s10886-024-01481-2.