Female mosquitoes depend on each other to choose the best breeding grounds – and with the arrival of spring, they are already on the hunt

By | March 19, 2024

Aedes aegypti Mosquitoes, one of the most common species in the US, love everything about people. They like our body heat and scents, which helps them find us. They love to feed on our blood to mature their eggs. In fact, they love all the standing water we create. Uncovered containers, old tires and junk piles collect water and are perfect for breeding.

And with the arrival of warm weather in the southern US, mosquito breeding season has already begun.

Considering all the options out there Aedes How do these cosmopolitan mosquitoes find the perfect place to lay their eggs in urban areas? Scientists previously thought this was a solitary act, but now research shows this is female Aedes aegypti Mosquitoes – the leading vector in the US for diseases like Zika, dengue, chikungunya and other viruses – can rely on each other for good assessments of breeding sites.

Our Laboratory of Tropical Genetics at Florida International University discovered a new behavior in which these mosquitoes work together to find suitable egg-laying sites. These findings, recently published in Communications Biology, show that mosquitoes regulate their own population density at breeding sites – an insight that could inform future mosquito control efforts.

About half a dozen mosquitoes spread along the inside of a container.About half a dozen mosquitoes spread along the inside of a container.
Aedes aegypti female mosquitoes lay their eggs in a laboratory breeding container. Kaylee Marrero, CC BY-ND

Where and why female mosquitoes cluster

Scientists know that female mosquitoes can be picky about where they lay their eggs. Aedes aegypti look for man-made nesting sites with relatively clean water, such as birdbaths, tires, or even water-filled trash. But given two equal choices, you would expect them to be evenly distributed between the two.

On the contrary, when we released females in a two-choice test where both breeding site options were equivalent, we repeatedly found more mosquitoes in one chamber than in the other. Furthermore, this happened regardless of where the preferred chamber was placed, whether the mosquitoes could touch water or whether mosquito eggs were already present at the breeding sites.

Female mosquitoes clearly followed each other in small groups to one breeding site rather than another – a newly discovered behavior Aedes aegypti we call that aggregation.

Two bowls, one with a few black spots in it, the other with many spots.Two bowls, one with a few black spots in it, the other with many spots.

Apparently the insects preferred not to lay their eggs alone. When we tested 30 mosquitoes in our trials, they chose one spot over the others by a margin of 2 to 1. However, this changed when the test population grew beyond 30 mosquitoes. When we tested 60 or 90 females, the aggregation disappeared.

This tells us that females can regulate their own density at breeding sites – a response that is likely a mechanism to limit larval competition.

Mosquitoes smell each other

Mosquitoes sense the world largely through smell, using three families of olfactory receptors. These receptors detect odors when females choose where to lay eggs. But how do females sense each other to regulate their density at breeding sites?

We investigated this question by first placing 15 mosquitoes at one of our two test breeding sites. Other females looking for a place to lie preferred an uninhabited spot to one that was already occupied, even though we had already seen that the mosquitoes preferred not to lay their eggs alone. Something led them away from the occupied breeding ground; we speculated that it could be carbon dioxide, which is an important signal for mosquitoes at all stages of their life cycle.

When female mosquitoes are looking for a blood meal, they fly toward the odor of CO₂, which all vertebrates exhale and release through their skin. After feeding they fly away, probably to avoid the risk of being killed by the host.

Mosquitoes also emit CO₂, and other mosquitoes can normally smell it, thanks to a receptor component called Gr3 in their olfactory organs. But when we released mutant females without a functional Gr3 receptor to find a place to lay eggs in our two-site test, we found that these insects, which couldn’t detect CO₂, were willing to lay their eggs in busy breeding grounds . This suggested that normal mosquitoes might avoid the preoccupied laying site because they smelled CO₂ emitted by mosquitoes already there.

To confirm this, we offered two unoccupied nesting sites to females looking for a place to lay. However, we have increased the CO₂ level around one of the sites to between 600 and 750 parts per million, compared to the normal level of approximately 450 to 500 ppm at the other site. We found that Aedes aegypti females avoided the unoccupied sites with elevated CO₂. This behavior appears intended to prevent occupied breeding grounds from becoming too crowded.

Overall, we found that two families of receptors play a role in the interactions between them Aedes aegypti females when looking for breeding grounds. Odor receptors detect an unfamiliar scent, which attracts females to a spot; Taste receptors detect CO₂, which discourages females from visiting breeding grounds when carbon dioxide levels are high. The balance between these attractive and repulsive scents will ultimately determine whether a female chooses or avoids a particular spot.

Image showing common mosquito breeding areas in and around the home, including gutters and pet bowls.Image showing common mosquito breeding areas in and around the home, including gutters and pet bowls.

Implications for mosquito control

Suppressing mosquito populations in urban areas using biolarvicides – pesticides made from live bacteria that are toxic to mosquito larvae – is a primary control strategy to limit the spread of deadly diseases such as West Nile virus and Zika virus. This is especially true for Aedes aegypti, the most common urban mosquito species that breeds in artificial breeding grounds that humans create. Other control tactics, such as spraying pesticides over large areas, target beneficial insects as well as mosquitoes and can be controversial.

Know that woman Aedes aegypti using social cues to choose the best nesting sites for their young and abandoning a nesting site when it becomes too crowded could lead to new control measures. Interrupting the reproductive cycle of female mosquitoes would reduce the spread of mosquitoes and the spread of diseases these insects carry.

This article is republished from The Conversation, an independent nonprofit organization providing facts and trusted analysis to help you understand our complex world. It was written by: Kaylee Marrero, Florida International University; André Luis da Costa da Silva, Florida International Universityand Matthew DeGennaro, Florida International University

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Kaylee Marrero receives funding from the National Institutes of Health.

Andre Luis Costa-da-Silva receives funding from the Centers for Disease Control and Prevention, the Southeastern Center of Excellence in Vector-borne Disease, and the National Institutes of Health. The opinions expressed in this article are his own.

Matthew DeGennaro receives funding from the Centers for Disease Control and Prevention (CDC), the Southeastern Center of Excellence in Vector-borne Disease, and the National Institutes of Health. The opinions expressed in this article are his own.

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