Taking a tsetse fly’s eye view of visual baits may help in the fight against sleeping sickness

Dr. Roger Santer

Dr Roger Santer, scientist and lecturer in Zoology at the Institute of Biological, Environmental and Rural Sciences (IBERS), Aberystwyth University, has taken a novel approach to understand how tsetse flies see coloured visual baits, and why they are attracted to different colours.

Santer’s findings, published this week in the journal PLOS Neglected Tropical Diseases, will help fine-tune visual baits for the more effective trapping of tsetse flies, and the control of the tropical disease that they spread.

Tsetse flies transmit human African trypanosomiasis or ‘Sleeping Sickness’ in sub-Saharan Africa. This potentially fatal disease is spread by the bite of an infected tsetse fly, eventually causing the victim to suffer a parasitic infection of the brain and the meninges (the covering of the brain and spinal cord).

Coloured baits and traps are used to kill or catch tsetse flies, and are one of the most effective ways of controlling the spread of the disease. However, further optimizing these devices is crucial in the fight against sleeping sickness.

Previous studies have tried to determine the best colour for visual baits by relating their light reflectance properties to their attractiveness to tsetse. However, as Santer explains, “the key to optimizing these visual baits may be to look at them through the eyes of a tsetse fly”.

The eyes of flies and humans have different types and numbers of photoreceptors (sensory cells that respond to different wavelengths of light reflected from an object like a visual bait), which means that they don’t perceive colours in the same way.

The novelty in Santer’s work was that he calculated the excitation of each fly photoreceptor type by the visual baits used to catch tsetse flies in three previous field studies. Effectively, he worked out the fly’s eye view of these visual baits.

Santer then used these calculated photoreceptor excitations to work out what attracted tsetse flies to visual baits. He found that tsetse fly attraction could be explained by a simple mechanism in the fly’s nervous system that compares the relative excitations of three different photoreceptor types.

Dr Santer says “By understanding the mechanism that causes tsetse flies to be attracted to visual baits, we can select colors for visual baits that cause tsetse to be even more strongly attracted. By doing that, we should be able to catch more tsetse and better control the spread of sleeping sickness”.

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