Fig. 1: Set-up for testing IR radiation as a potential host-associated cue.

a, Known host-associated sensory cues. b, Modes of thermal energy transfer: convection, conduction and IR radiation. The peak emission wavelength (λ^M) of emitting bodies at 34 °C is around 9.4 µm. c, The host-associated cues presented during the assay: human odour, 5% (v/v) CO₂ and heat in the form of IR radiation. Assay cages were 4 cm from the arena wall that housed the Peltier device to mitigate the effect of convective cues. Human odour was applied uniformly on the outside of the mesh of the assay cage from a used nitrile glove. CO₂ was delivered through perforated tubing, which formed a perimeter around both the control and IR zones. d, The Peltier device housing. An IR-transparent polyethylene (PE) film blocked convective cues from reaching the mosquitoes. e, Schematic of the behavioural assay. Mosquitoes were presented with IR and their host-seeking behaviour was video recorded for 5 min. f, Representative video frame taken from an experiment in which females were exposed to human odour and 5% CO₂. One zone was exposed to 34 °C radiant heat from a Peltier device. The Peltier device behind the other zone was off, and equilibrated to the ambient temperature (temp.) (29.5 °C). The position of each host-seeking mosquito was recorded during the experimental window. In all of the experiments in which CO₂ was provided, it was applied using the indicated time series (in seconds) unless otherwise stated. g, The PI, calculated from the indicated formula, using the total number of host-seeking observations in each zone during the 5 min experiment. PI < 0 indicates preference for zone 1; PI > 0 indicates preference for zone 2.