Visual threat avoidance while host seeking by Aedes aegypti mosquitoes.

The mosquito Aedes aegypti infects hundreds of millions of people annually with disease-causing viruses. When a mosquito approaches a host, the host often swats defensively. Here, we reveal the mosquito's escape behavior during host seeking in response to a threatening visual cue-a newly appearing shadow. We found that reactions to a shadow are far more aversive when it appears quickly versus slowly. Remarkably, mosquitoes evade shadows under very dim light conditions. Knockout of the TRP channel compromises the ability of mosquitoes to avoid threatening shadows, but only under high light conditions. Conversely, removing two of the five rhodopsins normally present in the compound eyes, Op1 and Op2, diminishes shadow aversion, but only under low light. Upon removal of a threatening visual cue, mosquitoes quickly re-initiate host seeking. Thus, female Aedes balance their need to host seek with visual threat avoidance by rapidly transitioning between these two behavioral states.