Most traps are black and blue. Is the particular shade of blue important?
Yes! For the targets made from cotton, the dye on the blue cloth components of all types of trap and target should be Phthalogen Blue. It is highly resistant to fading by sunlight and it has the reflectance that is most effective for producing the required type of responses from tsetse.
Beware of other blue dyes that look much like Phthalogen Blue to the human eye -- tsetse see quite differently from humans, and they are especially good at distinguishing between colours that we see as virtually identical.
Pthalogen blue cannot be used with polyester and synthetic fabrics but reputable manufacturers of targets have identified dyes that produce highly attractive targets that are colour-fast and long-lasting.
Black is black, isn’t it?
The black must be intensely black, and must remain so after prolonged exposure to sunlight. The specification found most satisfactory in Zimbabwe for cotton fabric is double-dying with acid sulphur dyes -- double dying means dying the cloth once and then putting it through the dye again.
Of course, it is very easy to make the above specification to the supplier, but impossible to check instantly that the cloth delivered is dyed as required. The only sure test is to leave the cloth exposed for several months.
Beware of suppliers who dye the cloth just once, with a cheap ULV-sensitive dye. Other tricks include taking cloth originally dyed, say, green, dying it just once again with black, and then claiming that the double-dying requirements are met. In both cases the black will become a light grey – or green – after being exposed to the sun.
The manufacturer of traps or targets can also be fooled by the cloth supplier in this way. However, reputable manufactures will usually supply replacements. The moral: choose a reputable supplier that is likely to be still be in business if you come to complain.
Green, C.H. (1986). Effects of colours and synthetic odours on the attraction of Glossina pallidipes and Glossina morsitans morsitans to traps and screens. Physiological Entomology 11, 411-421.
Green, C.H. (1988). The effect of colour on trap- and screen-orientated responses in Glossina palpalis palpalis Robineau-Desvoidy (Diptera: Glossinidae). Bulletin of Entomological Research 78, 591-604.
Lindh, J.M., Goswami, P., Blackburn, R.S., Arnold, S.E.J., Vale, G.A., Lehane, M.J., Torr, S.J. (2012). Optimizing the colour and fabric of targets for the control of the tsetse fly Glossina fuscipes fuscipes. PLoS Neglected Tropical Diseases 6.
Santer, R.D., Vale, G.A., Tsikire, D., Torr, S.J. (2019). Optimising targets for tsetse control: taking a fly's-eye-view to improve the colour of synthetic fabrics. PLoS Neglected Tropical Diseases 13.