Tsetse fly control — DTM&H MCQ

Correct answer: D — Blue-black cloth targets with insecticide

The correct answer is D, blue-black cloth targets with insecticide. Tsetse flies (Glossina spp) locate hosts using a combination of olfactory cues (CO2, host odours) and strong visual attraction to specific colours, particularly blue and black, which mimic the shade and contrast of large mammalian hosts and resting sites. Field studies from tsetse-endemic Africa (including Chad and neighbouring countries under the PATTEC/PAAT tsetse control programmes) have shown that phthalogen blue or black cloth panels, impregnated with a pyrethroid insecticide such as deltamethrin, exploit this innate colour preference: flies land on the target and pick up a lethal insecticide dose. This visual-lure-and-kill strategy is now the mainstay of large-scale, low-cost riverine tsetse control across the Glossina belt. Why the other options are wrong: A. CDC light traps with UV: UV light traps exploit phototaxis in mosquitoes and other nocturnal Diptera; Glossina are day-active and are not preferentially attracted to UV light, so these traps are not used for tsetse. C. Pyrethrum spray catch indoors: this is a technique for sampling indoor-resting malaria mosquitoes to assess indoor vector density, exploiting resting behaviour rather than visual attraction, and is irrelevant to exophilic tsetse. E. Oviposition traps near water: tsetse are larviparous, depositing a single mature larva directly into soil rather than laying eggs in water, so oviposition traps (used for culicine mosquitoes) have no application. B. Sugar-baited toxic traps: these exploit sugar-feeding behaviour seen in many mosquito species; tsetse are obligate blood feeders in both sexes and do not respond to sugar baits. Key point: Tsetse control targets exploit innate visual attraction to blue and black colours, distinguishing them from mosquito control tools that rely on light, resting behaviour, oviposition sites, or sugar feeding.

Reference: WHO/FAO, Vector control and the elimination of gambiense human African trypanosomiasis (HAT), Joint FAO/WHO Virtual Expert Meeting report, 2021, https://www.who.int/publications/i/item/9789240051867