In a pioneering study, researchers at the University of California, Santa Barbara, harnessed CRISPR-Cas9 gene-editing for the first time to impair Aedes aegypti mosquitoes' ability to detect dark silhouettes—the visual cues they use to identify potential hosts.
Mosquitoes' attraction to dark colors has been documented since the late 1930s, yet the molecular basis of their visual host-seeking remained elusive—until now. A team led by UC Santa Barbara experts has decoded key aspects of how Aedes aegypti uses vision to locate bite targets, as detailed in Current Biology.
"The better we understand how they perceive humans, the better we can control mosquitoes ecologically," says lead author Yinpeng Zhan.
These daytime hunters, active mainly at dawn and dusk, rely on multiple cues like CO2 plumes, skin heat, and humidity. "But absent a suitable host, they zero in on the nearest dark spot in their visual field," explains co-author Craig Montell, a renowned entomologist.
Focusing on Aedes aegypti—the primary vector for dengue, Zika, chikungunya, and yellow fever, infecting tens of millions annually—researchers zeroed in on five photosensitive proteins in their eyes. Females require blood meals for egg development.
Using CRISPR-Cas9, the team knocked out Op1, the most abundant rhodopsin in photoreceptor cells. In cage tests with black and white circles, about ten adult females showed no change, still preferring black.
Targeting Op2, closely related to Op1, yielded similar results. Only when both opsins were eliminated did mutants lose preference for dark targets, even after CO2 exposure—abolishing their visual host-targeting.
Further tests revealed no: All groups showed phototaxis toward light post-CO2, distinguished shadows and motion, had intact eye morphology, no retinal degeneration, and normal light responses. They were not blind, just unable to detect dark colors.
While engineered mosquitoes haven't yet faced live hosts, this visual deficit could hinder blood-feeding. "Vision is crucial for blood-feeding insects like mosquitoes, all disease vectors. This is the first molecular insight into this behavior," notes Montell.
These findings could shape innovative mosquito control strategies, potentially reducing populations by starving females of blood needed for reproduction.
