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New methods shed light on tsetse fly attraction to visual baits, and may help optimize tsetse traps and combat Sleeping Sickness

Dr. , 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 see colored visual baits, and why they are attracted to different colors. Santer’s findings, published 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 , eventually causing the victim to suffer a parasitic infection of the brain and the meninges (the covering of the brain and spinal cord). Colored 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 color 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 colors 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”.

Source

A Colour Opponent Model That Explains Tsetse Fly Attraction to Visual Baits and Can Be Used to Investigate More Efficacious Bait Materials, Roger D. Santer, PLOS Neglected Tropical Diseases, doi:10.1371/journal.pntd.0003360, published 4 December 2014.