MOSQUITO BYTES NEWSLETTER |
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ALL MOSQUITOES ARE NOT THE SAME
How Newly Discovered Invasive Aedes aegypti Mosquitoes Differ from the West Nile virus Mosquitoes Already in Contra Costa County
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West Nile virus (WNV) first appeared in Contra Costa County in 2004. During the 18 years since then, County residents have become used to the Contra Costa Mosquito & Vector Control District's (District) message that it's important to dump out standing water to prevent mosquitoes because mosquitoes need to develop from egg to adults in water. |
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Now, the District's message is that it's important to Dump and Scrub to prevent mosquitoes. Why has the message changed? The message changed because the District has found a new species of mosquito in Contra Costa County — one that is not native to Contra Costa County or California — and it's a mosquito that we do not want to become established here because it can spread additional diseases that our existing mosquitoes do not. It has other differences as well because all mosquitoes are not the same. Let's compare Contra Costa County's WNV mosquitoes to these new Aedes aegypti mosquitoes. |
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Culex pipiens mosquitoes are found throughout Northern California. |
WNV Mosquitoes
Disease Risk
- WNV is a virus that infects certain birds, typically in the Corvid family (crows and jays.)
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Culex mosquitoes prefer biting birds and can become infected with WNV after biting an infected bird.
- An infected mosquito can then spread WNV by biting another bird, mammal, or human.
- These mosquitoes cannot transmit the virus from person to person. Humans are considered dead-end hosts for WNV.
The Eggs
WNV mosquitoes produce egg rafts which contain, on average, 100 - 300 mosquito eggs all stuck together.
- These egg rafts float on the surface of the water in natural sites like creeks and ponds, or in artificial containers such as rain barrels, neglected swimming pools, or horse troughs where the eggs can develop into adult mosquitoes within 7-14 days.
- Dumping out water can kill the egg rafts and deny mosquitoes a place to develop.
- Once the egg rafts are out of the water, they are unable to hatch and are no longer viable.
When They Bite
WNV mosquitoes are known to be most active in the hours just before and after dawn and dusk, and they will bite a person on any area of exposed skin.
What They Look Like
Culex mosquitoes that can transmit WNV are considered medium-sized mosquitoes. They can vary in color but tend to be brown with light markings.
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Aedes aegypti are not native to California but have already become widespread through Southern and Central California.
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Aedes aegypti Mosquitoes
Disease Risk
Aedes aegypti mosquitoes are not native to Contra Costa County and are capable of spreading viruses including Zika, Chikungunya, Dengue, and Yellow fever.
- This mosquito prefers biting people and becomes infected by biting infected people, so if Aedes aegypti become established in Contra Costa County, one infected person can potentially become the source of a disease outbreak.
- While these diseases are not common in California, a few travel-related cases are reported every year.
The Eggs
Aedes aegypti mosquitoes lay individual sticky eggs in small containers that can hold water including buckets, jars, birdbaths, and plant saucers.
- These eggs, which look like tiny footballs, stick to the inside of containers along the water line. When the eggs become submerged, they will hatch and develop into adult mosquitoes within about a week.
- Because they are sticky, the eggs are not removed when the water is dumped out. That is why is important to dump out the water at least weekly and scrub the eggs off of the container before reusing it. Using a toilet brush or bottle brush along with a mild bleach solution (10%) will help kill the eggs.
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Aedes aegypti eggs can remain viable for months, so, for example, if a bucket containing eggs is stored for the winter and put back outside next spring, once it fills with sprinkler or rainwater, the eggs will hatch and will develop into adults capable of spreading disease.
When They Bite
Aedes aegypti mosquitoes are known to bite people during the day and they are known as "ankle biters" that will often bite legs or feet.
What They Look Like
Aedes aegypti are very small, about a 1/4 of an inch (about the size of a pencil eraser). They have black legs and bodies with white stripes.
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What Can We All Do To Prevent These New Mosquitoes
As you can see, while these new mosquitoes also have the ability to transmit disease, they are very different in their behavior and biology. District employees are currently going door-to-door in Martinez where the Aedes aegypti were first found, to inspect front and backyards to look for and eliminate these invasive mosquitoes before they become permanently established and spread to other areas of Contra Costa County.
The best thing Contra Costa County residents can do is dump out standing water at least weekly and scrub containers to remove any Aedes aegypti eggs and contact the District to report any day-biting mosquitoes.
Together, we can stop these new mosquitoes from making Contra Costa County their new home.
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Contra Costa Mosquito & Vector Control District, an independent special district and public health agency, is located at 155 Mason Circle in Concord. Contact the District to report mosquito and vector problems online or at (925) 685-9301. |
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