HOUSTON (CW39) – This week we are working in the weather to find out weather’s impact on mosquito populations in Southeastern Texas. There are some colder months where mosquito populations start to decrease, but the Harris County Public Health Mosquito Vector is trapping and testing mosquitoes year-round.
“Any time the temperatures start to warm up the mosquito populations start to increase. Especially if you combine that warming with the recent rain like we had this past week. We expect to start to see some nuisance mosquito populations start to increase, and the overall mosquito population to increase. This will cause for viral activity to rise.”, says Chris Fredregill with Harris County Public Health.
Mosquitoes are small so a lot of them quite literally freeze if the temperatures drop.
“They also get their energy from the environment, so they go to areas that are warm so that they don’t freeze. They go into storm sewers, or up against houses, so that way that can hide and get through the freeze. They lay low until it warms back up and they are ready to come back out. Other species go through the entire winter as eggs.”, says Chris.
It is only the ladies that we need to watch out for.
Chris states, “Only the female mosquito feeds on blood. She uses it to mature the eggs so that they can hatch. They will however, feed on all types of blood, but they do have their preferences. Some species prefer large mammals some prefer people, the Asian tiger mosquito being one of those, and some species prefer birds. As for day-to-day energy, they rely on nectar that they get from plants.”
Some mosquitoes do preferer different individuals over others.
Chris adds, “It depends on who you read… some folks say it is due to blood type. Some say that it is due to different chemicals in the skin. It is more than likely a number of factors that result in that attraction.”
Can the food you eat, or things you do, cause mosquitoes to prefer you over other people?
“It can…”, he replies.
“Anytime you are doing something that causes you to release a lot of CO2, which is primarily what they key in on, will bring them in closer. At a distance they kind of see large objects, then they sense the CO2. As they get closer, they land on you, sense the body heat and chemicals and that is when they decide if they want to feed on you or not.”, Chris adds
There are multiple active ingredients in repellants. There is deet, which is the one that most people know of. There is picaridin, IR3535, and oil of lemon eucalyptus. They all act in a variety of different ways.
“Some of them have a strict repellency. The mosquitoes just don’t like that. Others just mask the scent so that the mosquitoes don’t think you are a food source.”, says Chris.
Harris county is approximately 18,000 square miles and we cover the entirety of it. We set out about 300-400 trap a week and bring those mosquitoes back into the laboratory and test them for all of the mosquito borne diseases.
“We are out collecting and testing mosquitoes every single week. It is a robust network so that we can monitor these populations and keep everyone safe. We do find West Nile on an annual basis. It is an endemic disease in Harris County. With the rest of the mosquito borne diseases… zika, dengue, and chikungunya… our populations have never tested positive.”, he adds.
How can residents do their part in mitigating mosquitos in their yard, thus mitigating mosquitos throughout the city, and lowering the threat for disease?
Chris states, “There are several things that Harris County residents can do to help us out. Thay can take care of a lot of mosquito issues that are occurring on their property. One of the common areas that we find mosquitoes and mosquito larvae is in bird baths! This is very easily fixed. A resident can simply pour the water out, rub it with a brush, and refill it with fresh water. The key for residents to remember is to eliminate any water that stands for more than 5 days. Tires are also very good at collecting water. Mosquitoes will breed inside of the tires, broken playground equipment, and kiddie pools. If you eliminate areas where mosquitoes can breed in your yard, not only are you limiting the frequency that you’ll be bitten, but also you will be doing your part in lowering the potential for mosquito borne disease. You will not only be helping yourself, but your neighbors as well.”
Most residents have probably seen one of the spraying trucks or at least heard them in the middle of the night.
“Harris County Public Health will treat for adult mosquitoes under two conditions. That if we have confirmed mosquito borne diseases in an area. Or if we have a declared disaster and the mosquito populations are interfering with the response and recovery efforts. We use two materials to treat adult mosquito populations. We use an organophosphate and a Pyrethrin based product which is a synthetic pyrethroid. These have been vetted by the EPA and we keep very strict records on the amount and the times of where we apply. We want to apply the exact amount necessary to kill the mosquitoes and not harm anything else.”, says Chris.
In a CDC miniature light trap, there is a cooler to keep dry ice in. This is carbon dioxide which attracts mosquitoes. Down here is a trap body which is basically a tube with a fan in it and a small light. The mosquitoes get sucked into it, and the fan is strong enough to keep them down here. These are the taps we hang down in storm sewer systems. To trap a specific mosquito in the storm sewer.
This one here is a trap that people will normally see. This is a gravid trap. We take that water that has been soaked in hay for two weeks and put it in the bottom. The mosquitoes wanting to lay eggs will fly in here and get pulled up and get captured in this net where they can’t get pulled out.
After mosquitoes are collected they are taken into the virology lab for the testing of mosquito borne diseases.