Thursday, July 1, 2021
UNT System HR is brings you UNT World experts with this periodic and always timely installation called "Ask An Expert." So, let's ask...
There's mosquitoes on the river, as the song goes, but there's also mosquitoes in my backyard, my front yard, in fact, everywhere I go -- mosquitoes! Is there anything to do during these hot and humid months to mitigate those little bloodsuckers? Glad you asked. Dr. James Kennedy of UNT's Department of Biological Sciences is here to help us make it through summertime without Texas' most annoying pest driving us insane. Read on for an education in mosquitoes.
Let's start with some background:
There are over 3,000 species (different types of mosquitoes in the world. Only a small percentage of the mosquito species carry diseases. In the United States, mosquito-borne diseases like Malaria and Yellow fever, once widespread, have been controlled. Dengue, breakbone fever, is present in Texas but is not a threat at this time to North Texas. West Nile Virus (WNV) was first reported in north central Texas in 2002 (more info below). Other mosquito-carried viruses such as chikungunya and Zika have emerged only very recently. Approximately 100 species of mosquitoes have been documented from Texas; 50 species of mosquitoes have been identified from Denton.
The lifecycle of a mosquito includes an egg – larva, pupa and adult stage. The egg, larvae and pupa are aquatic. The larvae of mosquitoes breath atmospheric air (just like humans). The pupa is also aquatic and breaths atmospheric air.
Mosquitoes larvae and pupae require still, stagnant water to complete their metamorphosis. Larval and pupa habitats range from wetlands, drainage ditches to tree holes. They are especially abundant when they are isolated from fish or other animals that may feed on the larva or pupa. Many mosquitoes have adapted to habitats created by man, i.e., rain gutters, pet dishes and discarded tires. The behaviors and habitats differ for different types of mosquitoes -- they are micro-habitat specialists. For example, there are mosquitoes categorized as floodwater species that occur after rain events. Floodwater mosquitoes have dormant eggs under dry conditions and hatch when there is sufficient rainfall to produce pools. Another group of mosquitoes is categorized as container-breeding mosquitoes. Container mosquitoes tend to lay their eggs in container-type habitats, i.e., pet dishes left outside, discarded drink cans that fill with irrigation or rainwater, saucers underneath flower pots and birdbaths.
It's interesting to note that most female mosquitoes have feeding preferences. There are mosquito species that adapted their behavior to feed on everything from amphibians, reptiles to mammals. However, most will not pass up the opportunity to take a blood meal from other animals. The most medically important mosquito in our area is Culex quinquefasciatus (southern house mosquito), which is discussed more below.
OK, on to the questions:
Let's start with the basics: What are the conditions that make mosquitoes so prevalent
in North Texas, and how did the weeks of rain we experienced in May, then immediately
followed by high temperatures and humidity, affect the mosquito population?
Any precipitation during the warm weather months can create standing/stagnant water and produce habitats for mosquitoes to lay their eggs. Warmer temperatures and high humidities will enable the mosquito to complete their lifecycle faster, allowing them to lay more eggs and increase their populations more quickly. In the spring or periods of heavy rain, mosquitoes known as floodwater mosquitoes will dominate. As the summer progresses, standing water usually becomes scarcer, and container breeding mosquitoes will become more common. However, heavy rains in the summer can and do change the mosquito species present.
Why do mosquitoes feast on blood, and are all mosquitoes blood suckers?
Both male and female mosquitoes have a long snout or proboscis that they use for feeding. Both sexes of adult mosquitoes feed on nectar, plant sap or honeydew for nourishment. Only adult female mosquitoes feed on blood. A blood meal provides the protein required for egg development. Except for blood meals, males and females have the same diet.
It can seem as though the moment you step outside that mosquitoes have a radar that
detects a food source is in its vicinity. How do they find us so quickly?
How mosquitoes find you is an active area of research and there is much to learn. It is not fully understood why some people are mosquito magnets while others are not. It is known that sights and odors attract mosquitoes. Mosquitoes are experts at detecting smells. A mosquito's antennae is covered with structures that can detect odors. The mosquito uses scents to find animals to feed on, nectar and places to lay their eggs. Carbon Dioxide is a universal attractant used to find a blood meal because all vertebrates emit it. Other body scents like a chemical called Octenol associated with large plant-eating animals, including humans, are also important. An interesting fact for those that like to barbeque and drink adult beverages is that scientific studies have shown that as the body breaks down the ingested beverages, chemicals released through perspiration attract mosquitoes.
Is there anything organic we can do to help reduce the amount of mosquitoes, say,
in our backyard where we might want to have friends over to grill burgers without
getting swarmed? What steps, such as eliminating standing water, can we take to reduce
mosquitoes breeding around our homes?
Mosquitoes breed in standing water. To reduce the number of mosquitoes in your yard, carefully check the property for any standing water and dump it. Pet dishes and birdbaths should be discarded every few days. If the water is permanent and can't be dumped or drained, use BTi (Bacillus thuringiensis israelensisto) to treat the water. This naturally occurring bacteria is available in a solid form, usually a ring or tablet. To treat a water body, BTi is simply tossed in the water. The City of Denton provides BTi to residents or can be purchased at retailers like Lowe's. BTi is a safe insecticide that only affects the larvae of mosquitoes. There is no toxicity to people.
is there a particular ingredient or anything specific we should look for in a product
when buying yard spray or skin spray/cream that works better than others?
I put the following information together for a group at Robson Ranch in response to questions they asked after a presentation I gave. A few questions came up about mosquito repellents during our discussion. I thought I would provide the following information based on reliable sources -- American Mosquito Control Association, the Centers for Disease Control and Consumer Reports. I want to emphasize I am not promoting or recommending any product, only presenting the information for people to consider. When purchasing an insect repellent, read the label for ingredients. Other chemicals in the repellents besides the active ingredient might cause an allergic reaction in some individuals.
- DEET is considered by many to be the "gold standard" in insect repellents. Products with 25 to 30 percent DEET provide long-lasting protection against mosquitoes and ticks. Higher concentrations of DEET are not necessary and may have effects on health.
- Picaridin is an effective alternative to DEET. This product is widely used in Europe but has only been available in the U.S. since around 2005.
- Oil of lemon eucalyptus (OLE), a natural product, has been recognized by the Centers for Disease Control as an effective insect repellent. Care should be taken to not confuse OLE with the similarly named Lemon Eucalyptus Oil. While both products are extracted from Eucalyptus trees, the extraction methods differ and Lemon Eucalyptus Oil is reported not to be an effective repellent.
Several comments were made about Vitamin B as a repellent. However, research has not shown any reduction in mosquito attraction.
If going to an outdoor event, what precautions should we take to minimize the risk of becoming dinner for mosquitoes? For instance, do Citronella candles or burners really work? Do you recommend backyard bug zappers? Are mosquito control companies worth the cost?
A common recommendation for personal protection from mosquitoes is to follow the 4Ds:
- Dusk – Dawn, are prime feeding times. Reduce time outdoors during these times
- Dress - Long pants and sleeves – light-colored is less attractive to mosquitoes.
- DEET - Use mosquito repellent – DEET is one, but there are others, see note below. Do not use DEET on animals
- Drain – eliminate standing water.
Bug zappers, sonic devices, CO2 devices (mosquito magnet) have no proven efficacy. It should also be noted that Bug Zappers also kill many beneficial insects.
West Nile Virus is always in the news during mosquito season. What is it, what is
the likelihood of contracting it and are there symptoms we should be aware of that
signal a doctor visit is necessary?
West Nile Virus (WNV) is a mosquito-borne disease caused by the bite of an infected mosquito. The WNV cycles between mosquitoes and birds. The virus replicates inside of infected birds and can develop high levels of the virus. Ornithophilous (bird-loving) mosquitoes are infected when they feed on those birds infected with the virus. The virus replicates in the mosquito and is passed off to more birds through their saliva when they bite. Mosquitoes infected with WNV will also bite humans and other mammals if given the opportunity. However, these are dead-end hosts because they do not develop high levels of the WNV sufficient to pass it off to other biting mosquitoes. There are other potential ways of transmitting WNV, such as blood transfusions, but this is rare. I believe donated blood is tested with WNV before being used.
WNV was first detected in Denton County in 2002 by my laboratory. In the nearly 20 years, my laboratory has been partnering with the City of Denton to monitor mosquito populations; 99% of the mosquitoes that tested positive for WNV have been the southern house mosquito Culex quinquefasciatus. This mosquito has a preference for feeding on birds, but will readily bite humans given the opportunity. This mosquito prefers to lay its eggs in containers holding water and readily adapts to habitats around homes.
The chances of getting WNV are minimal. Even if you are bitten and infected with the WNV, less than 80% will have symptoms. Those that do develop flu-like symptoms within a week or two after being bitten. Less than 1% of those that contact WNV will be infected with the neuroinvasive form that infects the brain and spinal cord. The neuroinvasive form of WNV is a severe illness and can cause paralysis and death. The symptoms of the neuroinvasive condition include severe headaches, neck pain, sensitivity to light and confusion. Older adults and people with immune-compromised systems are more susceptible to the neuroinvasive WNV.