Natures wonders: how mosquitos find dinner (Introduction)

by David Turell , Saturday, August 24, 2024, 19:35 (23 days ago) @ David Turell

Infared sensing is a strong possibility:

https://www.sciencedaily.com/releases/2024/08/240822181042.htm

"A team led by researchers at UC Santa Barbara has added another sense to the mosquito's documented repertoire: infrared detection. Infrared radiation from a source roughly the temperature of human skin doubled the insects' overall host-seeking behavior when combined with CO2 and human odor. The mosquitoes overwhelmingly navigated toward this infrared source while host seeking. The researchers also discovered where this infrared detector is located and how it works on a morphological and biochemical level.

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"It is well established that mosquitoes like Aedes aegypti use multiple cues to home in on hosts from a distance. "These include CO2 from our exhaled breath, odors, vision, [convection] heat from our skin, and humidity from our bodies," explained co-lead author Avinash Chandel, a current postdoc at UCSB in Montell's group. "However, each of these cues have limitations." The insects have poor vision, and a strong wind or rapid movement of the human host can throw off their tracking of the chemical senses. So the authors wondered if mosquitoes could detect a more reliable directional cue, like infrared radiation.

"Within about 10 cm, these insects can detect the heat rising from our skin. And they can directly sense the temperature of our skin once they land. These two senses correspond to two of the three kinds of heat transfer: convection, heat carried away by a medium like air, and conduction, heat via direct touch. But energy from heat can also travel longer distances when converted into electromagnetic waves, generally in the infrared (IR) range of the spectrum. The IR can then heat whatever it hits. Animals like pit vipers can sense thermal IR from warm prey, and the team wondered whether mosquitoes, like Aedes aegypti, could as well.

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"Adding thermal IR from a 34º Celcius source (about skin temperature) doubled the insects' host-seeking activity. This makes infrared radiation a newly documented sense that mosquitoes use to locate us. And the team discovered it remains effective up to about 70 cm (2.5 feet).

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"Scientists have known that the tips of a mosquito's antennae have heat-sensing neurons. And the team discovered that removing these tips eliminated the mosquitoes' ability to detect IR.

"Indeed, another lab found the temperature-sensitive protein, TRPA1, in the end of the antenna. And the UCSB team observed that animals without a functional trpA1 gene, which codes for the protein, couldn't detect IR.

"The tip of each antenna has peg-in-pit structures that are well adapted to sensing radiation. The pit shields the peg from conductive and convective heat, enabling the highly directional IR radiation to enter and warm up the structure. The mosquito then uses TRPA1 -- essentially a temperature sensor -- to detect infrared radiation.

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"Upon further investigation, the researchers discovered that two of the 10 rhodopsins found in mosquitoes are expressed in the same antennal neurons as TRPA1.

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"Their results indicated that more intense thermal IR -- like what a mosquito would experience at closer range (for example, around 1 foot) -- directly activates TRPA1. Meanwhile, Op1 and Op2 can get activated at lower levels of thermal IR, and then indirectly trigger TRPA1. Since our skin temperature is constant, extending the sensitivity of TRPA1 effectively extends the range of the mosquito's IR sensor to around 2.5 ft.

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"'Despite their diminutive size, mosquitoes are responsible for more human deaths than any other animal," DeBeaubien said. "Our research enhances the understanding of how mosquitoes target humans and offers new possibilities for controlling the transmission of mosquito-borne diseases.'"

Comment; From research: " By comparing their genes, the researchers determined that the Aedes aegypti mosquitoes probably evolved from an ancestral species on islands in the southwest Indian Ocean about 7 million years ago. And the research indicates the mosquitoes spread from the islands to the African mainland quite recently in evolutionary time, possibly within the last 25,000 to 17,000 years,..."

Comment continues: Among the thousands of mosquito species, Aedes carries five types of Plasmodium parasites which cause malaria of varying severity. Why they learned to bite humans is thought to be drought periods forcing them to look for other liquid sources.