Novel approaches to repel insect vectors

Abstract text

Introduction

The use of repellents can reduce the number of insect bites and thereby the risk of pathogen transmission. However, current repellents lack effectiveness as they only work for a limited time and must be applied directly on the skin. Biting midges (Culicoides spp.) are of major significance as vectors of veterinary pathogens. Like mosquitoes, they are attracted to their hosts by carbon dioxide in exhaled air and by their body odours, which are mainly produced by skin bacteria. This opens the possibility to protect animals from biting midges by supplementing the skin microbiome with probiotics that reduce their attractiveness. As another option to this probiotics approach, spatial repellents may be convenient as they eliminate the need to apply repellents directly onto the skin.

Objectives

Identify skin bacteria from sheep and spatial repellents that reduce biting by midges.

Materials & Methods

The skin bacterial composition of 89 adult female sheep from different breeds was determined by metabarcoding. Skin bacteria were cultivated on artificial media, and the attractiveness of selected isolates to biting midges determined in laboratory settings using a Y-tube olfactometer and membrane feeding assays. In addition, spatial repellency of different compounds was determined in a high-throughput tube setup and in a cage setup with automated tracking of the biting midges.

Results

We were able to detect repellent effects and a significant reduction in feeding rate of some of the skin bacteria tested. Next, a repellent bacterial strain will be applied on sheep in an exploratory study. Some of the tested spatial repellents were as effective as the golden standard DEET in the high-throughput tube setup. In addition, spatial repellency was observed in the cage setup and visualized by tracking and heatmaps. These spatial repellents will be tested in large scale semi-field experiments.

Conclusion

Applying skin probiotics could be a novel solution for long-lasting protection against biting insects, in contrast to the topical application of repellents that evaporate within hours, and spatial repellents could protect from a distance. These studies show that novel approaches to repel insect vectors may help to protect animals and humans against insect bites and thereby reduce pathogen transmission.

Funding: Gebert Rüf Stiftung (GRS-089/20); FAN UZH & Gebauer Stiftung; Federal Food Safety and Veterinary Office.