Prospects for Developing Odour Baits To Control Glossina fuscipes spp., the Major Vector of Human African Trypanosomiasis

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Abstract
We are attempting to develop cost-effective control methods for the important vector of sleeping sickness, Glossina fuscipes spp. Responses of the tsetse flies Glossina fuscipes fuscipes (in Kenya) and G. f. quanzensis (in Democratic Republic of Congo) to natural host odours are reported. Arrangements of electric nets were used to assess the effect of cattle-, human- and pig-odour on (1) the numbers of tsetse attracted to the odour source and (2) the proportion of flies that landed on a black target (1×1 m). In addition responses to monitor lizard (Varanus niloticus) were assessed in Kenya. The effects of all four odours on the proportion of tsetse that entered a biconical trap were also determined. Sources of natural host odour were produced by placing live hosts in a tent or metal hut (volumes≈16 m3) from which the air was exhausted at ∼2000 L/min. Odours from cattle, pigs and humans had no significant effect on attraction of G. f. fuscipes but lizard odour doubled the catch (PG. f. quanzensis, only pig odour had a consistent effect, doubling the catch of females attracted to the source and increasing the landing response for females by ∼15%. Dispensing CO2 at doses equivalent to natural hosts suggested that the response of G. f. fuscipes to lizard odour was not due to CO2. For G. f. quanzensis, pig odour and CO2 attracted similar numbers of tsetse, but CO2 had no material effect on the landing response. The results suggest that identifying kairomones present in lizard odour for G. f. fuscipes and pig odour for G. f. quanzensis may improve the performance of targets for controlling these species. Human African Trypanosomiasis (sleeping sickness) remains a serious threat to many of the poorest people in Africa. The trypanosomes causing the disease are transmitted by tsetse flies. There are no vaccines or prophylactic drugs to prevent people from contracting the disease. So the disease is dealt with after it has been contracted using often ineffective curative drugs with unpleasant and sometimes fatal side effects. Prospects for the development of effective vaccines or prophylactic drugs are poor. One certain means of preventing disease transmission is to remove tsetse flies, either at a local level (e.g., a group of villages) or regionally (covering large parts of a country or region). However, a major problem is the cost and logistical difficulty of implementing such fly control programmes. To overcome this, we are trying to develop cost-effective insecticide-treated targets by identifying chemicals that will increase the numbers of tsetse that will be lured to a target and killed. Here we show that two major vectors, G. f. fuscipes and G. f. quanzensis, are attracted to the odour of monitor lizards and pigs, respectively. This opens the way for further work to identify the attractants present in these natural odours which can be simply and cheaply incorporated into targets to reduce the cost of control.