Advantages and limitations of commercially available electrocuting grids for studying mosquito behaviour

Background: Mosquito feeding behaviour plays a major role in determining malaria transmission intensity and the impact of specific prevention measures. Human Landing Catch (HLC) is currently the only method that can directly and consistently measure the biting rates of anthropophagic mosquitoes, both indoors and outdoors. However, this method exposes the participant to mosquito-borne pathogens, therefore new exposure-free methods are needed to replace it. Methods: Commercially available electrocuting grids (EGs) were evaluated as an alternative to HLC using a Latin Square experimental design in Dar es Salaam, Tanzania. Both HLC and EGs were used to estimate the proportion of human exposure to mosquitoes occurring indoors (pi(i)), as well as its two underlying parameters: the proportion of mosquitoes caught indoors (P-i) and the proportion of mosquitoes caught between the first and last hour when most people are indoors (P-fl). Results: HLC and EGs methods accounted for 69% and 31% of the total number of female mosquitoes caught respectively and both methods caught more mosquitoes outdoors than indoors. Results from the gold standard HLC suggest that An. gambiae s.s. in Dar es Salaam is neither exophagic nor endophagic (P-i approximate to 0.5), whereas An. arabiensis is exophagic (P-i < < 0.5). Both species prefer to feed after 10pm when most people are indoors (P-fl > > 0.5). EGs yielded estimates of P-i for An. gambiae s.s., An. arabiensis and An. coustani, that were approximately equivalent to those with HLC but significantly underestimated P-fl for An. gambiae s.s. and An. coustani. The relative sampling sensitivity of EGs declined over the course of the night (p <= 0.001) for all mosquito taxa except An. arabiensis. Conclusions: Commercial EGs sample human-seeking mosquitoes with high sensitivity both indoors and outdoors and accurately measure the propensity of Anopheles malaria vectors to bite indoors rather than outdoors. However, further modifications are needed to stabilize sampling sensitivity over a full nocturnal cycle so that they can be used to survey patterns of human exposure to mosquitoes.