“We show that it is important to consider the fly’s-eye-view when designing tsetse targets, and our results challenge the traditional view that ‘blue’ and ‘black’ are the best colors for tsetse targets. In fact, because flies and humans have different photoreceptor machinery, human color descriptions are largely irrelevant to fly behavior”Roger Santer
A team of researchers has pioneered a new approach to designing colored fabrics for the devices used to attract and kill tsetse flies, and thus control sleeping sickness spread by their bites in sub-Saharan Africa. The team’s approach is based on an understanding of how flies see color, and its effectiveness was shown in field tests of fabrics in Zimbabwe.
The targets for controlling tsetse flies are traditionally large panels of black or blue cotton coated in insecticide, but there is a great need for such control devices to be as inexpensive and effective as possible. Modern polyesters are cheaper, lighter, more durable and retain insecticide better, but are sometimes not as effective in attracting tsetse as traditional cottons. As reported in the journal PLOS Neglected Tropical Diseases [Santer et al. PLoS Negl. Trop. Dis. (2019) DOI: 10.1371/journal.pntd.0007905], this new approach allowed them to design a prototype violet polyester fabric that attracted savannah tsetse flies more effectively than a standard cotton target.
Roger Santer, of Aberystwyth University, worked with a team of experts in tsetse ecology, behaviour and control. The researchers first calculated the response of a fly's photoreceptors to a range of previously tested fabrics to identify the attractive color properties from a fly’s point of view. Working with a textile company, they then designed and produced a fabric that displayed those attractive properties. In field tests they found that a commercial blue polyester target was just as effective as a traditional black cotton one, but that their violet polyester attracted approximately 50% more female tsetse than either the traditional black cotton or a more typical blue polyester.
The findings demonstrate that fly photoreceptor-based approaches can help to engineer fabrics with greater attractiveness to tsetse and demonstrate that their violet fabric is robust and effective. As Santer told Materials Today, “We show that it is important to consider the fly’s-eye-view when designing tsetse targets, and our results challenge the traditional view that ‘blue’ and ‘black’ are the best colors for tsetse targets. In fact, because flies and humans have different photoreceptor machinery, human color descriptions are largely irrelevant to fly behavior”. The researchers hope the fabrics can be implemented in tsetse control devices to enhance the effectiveness of vector control, and as their method is transferable to other species and contexts that it can be applied in the control of others insect pests and disease vectors.
The violet prototype and a typical blue polyester, with a reflectance probe and a white reflectance standard, part of the kit used for measuring color properties