Semi-field set up
The study was carried out in Western Kenya at the Centre for Global Health Research, Kenya Medical Research Institute, Kisumu. The release and recapture studies were conducted in a MalariaSphere a closed system 20m long x 8m wide(Knols et al. , 2002)with slanted roofing (3m in the sides and 4.5m in the middle). The entire structure is covered with insect-proof netting screen that prevents mosquitoes inside the system from escaping into the environment, or vice versa (Fig. 1 A). The system is also double doored for the same reason. Inside the systema3m x 3m mud-walled hut is erected resembling a typical house in the study village in terms of size, structure and mosquito exit/entry points (eaves, window,and door) (Fig. 1B). The structure has local vegetation and grass floor to mimic the natural vegetation and provide shelter for mosquitoes in the outdoor environment (Fig. 1B). Two round clay pots are installed in the enclosure but outside the hut to act as outdoor resting sites (Fig 1F).Inside the hut either a treated LLIN inside a bed-net trap (Mbita trap)or an untreated net inside a bed-net trap as control was hanged (Mathenge et al. , 2002). Treated and untreated nets were used at different nights in the same hut. For each night, a consented and remunerated human volunteer slept under the bed-net trap in the hut. To offset any personal bias due to differential sleeping habits or relative attractiveness to mosquitoes, two sleepers were recruited for this experiment and took turns to sleep under the bed net. They were instructed not to consume alcohol or smoke and avoid deodorants during the study period. The volunteer who slept under the bed net served as a bait to attract the mosquitoes into the hut but was not bitten because of the net shield.