Fig. 2: The contribution of orange-red wavelengths in attraction to faux human skin.

a Spectral reflectance of human skin and faux skin used in behavioral experiments. Lines are the mean and shaded area is the ±sem (n = 6). b Ultra-thin optical filters (450 nm, 600 nm, and 700 nm) attenuated discrete bands in the object’s reflected spectrum. c, d Occupancy maps of the mosquito’s distribution around the visual objects during exposure to CO₂. During CO₂, mosquitoes were significantly attracted to the faux skin color compared to the white (control) object (c). However, the optical filter attenuating the 550–630 nm band reduced the number of mosquitoes investigating the faux skin color (d). e, f Mosquitoes significantly preferred the faux human skin colors (e), although optical filters in the yellow to red wavelengths significantly decreased the attractiveness of the visual object (f). Boxplots are the mean (line) with 95% confidence interval (shaded area); letters denote statistically significant differences between groups. g Mosquito lines deficient in long-wavelength opsins (opsin1 and opsin2), or unable to detect CO₂ (Gr3 mutant), were tested in their attraction of human skin color. h Mean preference indices for the Gr3 mutants (blue) and opsin mutants (orange). All mosquito lines showed similar preferences to the white and skin color visual objects during exposure to filtered air (Kruskal–Wallis test: df = 3, Chi-sq = 1.68, P = 0.64). However, during CO₂ the lines were significantly different from one another in their visual preferences (Kruskal–Wallis test with multiple comparisons: df = 3, Chi-sq = 96.01, P < 0.001): only the heterozygote (Gr3^−/+) and wild-type (LVP) lines showed significant attraction to the skin color (one-sample t-test: P < 0.001), whereas the opsin double mutant line (op-1/op-2) and the Gr3^−/− mutants showed no attraction (one-sample two-tailed t-test: P > 0.31). Boxplots are the mean (line) with 95% confidence interval (shaded area) (n = 13,999; 15,035; 14,016; 48,624; 19,284; 20,713; 40,690; 26,135; 39,649; 16,208; 3,550; 9,277; 13,799; 10,948; and 5,679 mosquito trajectories for the Y02, Vile 45, Y10, R10, IR filter, coverslip, 450 nm filter, 600 nm filter, 700 nm filter, wt, Gr3^−/−, Gr3^−/+, op1-R, op-2G, and op1-R,op2-G treatments, respectively).