Esperanza Window Traps for the collection of anthropophilic blackflies (Diptera: Simuliidae) in Uganda and Tanzania

Abstract

There is an increasing need to evaluate the impact of chemotherapeutic and vector-based interventions as onchocerciasis affected countries work towards eliminating the disease. The Esperanza Window Trap (EWT) provides a possible alternative to human landing collections (HLCs) for the collection of anthropophilic blackflies, yet it is not known whether current designs will prove effective for onchocerciasis vectors throughout sub-Saharan Africa. EWTs were deployed for 41 days in northern Uganda and south eastern Tanzania where different Simulium damnosum sibling species are responsible for disease transmission. The relative efficacy of EWTs and HLCs was compared, and responses of host-seeking blackflies to odour baits, colours, and yeast-produced CO2 were investigated. Blue EWTs baited with CO2 and worn socks collected 42.3% (2,393) of the total S. damnosum s.l. catch in northern Uganda. Numbers were comparable with those collected by HLCs (32.1%, 1,817), and higher than those collected on traps baited with CO2 and BG-Lure (25.6%, 1,446), a synthetic human attractant. Traps performed less well for the collection of S. damnosum s.l. in Tanzania where HLCs (72.5%, 2,432) consistently outperformed both blue (16.8%, 563) and black (10.7%, 360) traps baited with CO2 and worn socks. HLCs (72.3%, 361) also outperformed sock-baited (6.4%, 32) and BG-Lure-baited (21.2%, 106) traps for the collection of anthropophilic Simulium bovis in northern Uganda. Contrasting blackfly distributions were observed on traps in Uganda and Tanzania, indicating differences in behaviour in each area. The success of EWT collections of S. damnosum s.l. in northern Uganda was not replicated in Tanzania, or for the collection of anthropophilic S. bovis. Further research to improve the understanding of behavioural responses of vector sibling species to traps and their attractants should be encouraged.

The Search for an Efficient Black Fly Trap for Xenomonitoring of Onchocerciasis

“…In another study by Hendy et al (2017), some further field testing of the EWTs was carried out [ 21 ] with the aim of optimizing the design for enhanced efficiency. The investigators built these traps based on previously published methods [ 19 ] to evaluate their efficacy and ease of use.…”

“…However, the traps were less effective at collecting the same species in Tanzania. They opined that black fly behaviour and response to traps will probably vary from one country to another and that though the EWTs showed promise for black fly collections, further research and development were needed to determine how broadly they can be used [ 21 ].…”

“…However, some questions still beg for answers with regard to the usage of EWTs and there is need for further research in this area. The first challenge encountered is that some authors report difficulties in the availability of the insect adhesives [ 21 ] used to trap the black flies in EWTs. Also the challenge with the cost of these adhesives even when they are available and the difficulties with application have been discussed [ 24 ].…”

“…In the face of global elimination efforts and targets, there is an urgent need to develop vector traps which can effectively replace HLCs in disease monitoring and surveillance. Several traps have been tested for their potential to capture host seeking black fly species for disease monitoring [ 10 – 14 , 19 – 21 , 23 , 24 ]; however the most promising of such traps in recent times is the EWTs. These traps have clearly demonstrated promise in their ability to replace HLCs and may provide an added advantage as a means to control black fly populations if they are deployed in large numbers in endemic communities.…”

From river blindness control to elimination: bridge over troubled water

“…In Ghana, we have tried a number of strategies, including host-dependent and host-independent catching methods [ 73 , 75 ], and others have tried to develop and optimise (e.g. Esperanza window) traps that would obviate the need for human attractants [ 76 , 77 ]. The advantage of human landing catches is their comparative value with the standardised methods used by the OCP [ 78 ].…”