Figure 4. Fast light-to-dark shadows trigger an escape response.
(A–D) (Left) Cartoons of setups for the control experiments. (Right) Distributions of spontaneous takeoffs from 20,000 random samples in each videos set (see STAR Methods). The mean spontaneous takeoff rate ( TO; red) was determined via random sampling. The observed takeoff rate (obs. TO; purple) is the takeoff rate in response to the stimulus. Normalized takeoffs represent the difference between TO and obs. TO. (A) Shadow-movement experiment. (B) Flash light off.
(C) No light block (LB). (D) LB apparatus moved but positioned so that no shadow is cast.
(E) Normalized takeoffs from protocols depicted in (A–D). One-way ANOVA (p< 0.001) followed by Tukey’s honestly significant difference (HSD) test.
(F) Effects of shadow speed and polarity on takeoffs. ON-edge shadows (blue dots), and OFF-edge shadows (orange dots). Speeds tested for ON- and OFF-edge shadows: 60, 31, and 15 cm/s. Additional speeds for OFF-edge shadows: 8 and 4 cm/s. One-way ANOVA (p < 0.001) followed by Tukey’s HSD test. (E–F) n = six cages with 30 mosquitoes/condition, each recorded three times.
(G) Polar histogram displaying probability of mosquito orientation on the back cage wall. Orientations subdivided into four groups each spanning 60° to specify mosquitoes facing up, down, left, or right. Probabilities from 29,312 landing events from 36 cages of 30 mosquitoes.
(H) Normalized takeoffs by mosquitoes facing up vs. down.
(I) Normalized takeoffs by mosquitoes facing left versus right. (H and I), Two-tailed unpaired Student’s t tests. p > 0.05. (G–I), n = 6, each consisting of six cages of 30 mosquitoes measured three times each.
(J) Heatmap displaying effects of shadow speed and light intensity on normalized takeoffs (Norm. takeoffs) for OFF-edge shadows. Columns, light intensity. Rows, shadow speed. n = 6 cages of 30 mosquitoes per condition, each recorded three times. ***p < 0.001. Means ± SEMs. See also Figure S2.