Activation (A) and taxis movement (B) of A. gambiae s.s. towards stimuli in the semi-field tunnel. Model-estimated proportion of A. arabiensis mosquitoes A) moving out of the middle chamber either towards or away from the point of stimulation (= activation) or B) moving towards the point of stimulation (= taxis) by distance for control nights, i.e. no stimulus (filled circle), 500 ml min-1 CO2 (open circle), synthetic odour blend + 500 ml min-1 CO2 (open square) and a human volunteer (open diamond) in the open field environment (Experiment 2). Each point represents the model –estimated proportion from the best-fitting model, with the associated 95% confidence intervals  indicated by vertical bars. NB. At each distance, the data points for the four treatments are slightly offset from one another to improve clarity.