Merely mention mosquito control to most people and you will soon hear talk of West Nile Virus, low-flying helicopters at dawn, or possibly even how their dog was never seen again after it was carried away by two hungry "biting flies."
When the West Nile Virus first exploded on the scene way back in 1999, people immediately began to take a greater interest in mosquitoes and the places where they live and breed.
Since, by their very nature, water and wastewater systems seem to abound with water (a necessary element for the miracle of birth in mosquitoes), it's important that systems take the time to prepare a plan for controlling mosquitoes in and around their system.
For the sake of argument, let's call your system's mosquito control policy an Integrated Pest Management Plan. Even if it only consists of nothing more invasive than a quick slap of the hand or good fly swatter, it is important that system employees know what is permissible when it comes to getting rid of pesky mosquitoes and how to reduce potential breeding grounds. After all, the most common method of controlling mosquitoes generally involves the use of poisonous pesticides, a practice that can have dire effects on the safety of the water you are treating and your customer's health.
In this issue of the Safe Drinking Water Trust eBulletin we'll take a look at why it's important to keep mosquitoes under control and out of your system. Through a few simple "best practices," every system can play a role in reducing the mosquito population and keeping their customers healthy so that they continue drinking water for a long time to come.
Additional Resources
American Mosquito Control Association
www.mosquito.org [1]
Some Like it Hot
In the U.S. there are more than 200 species of mosquitoes, each requiring a source of water to reproduce. Since some mosquitoes are capable of transmitting diseases such as malaria, yellow fever, dengue, filariasis, and several types of encephalitis including West Nile Virus, keeping their populations down should be a priority of every red-blooded American.
In order to better understand how to control the mosquito population, it is important to recognize that a mosquito goes through four separate and distinct stages in its life cycle: egg, larva, pupa, and adult.
Eggs can be laid one-at-a-time or in large groups called "rafts" depending on the species. These "rafts" can often included up to 200 eggs. While clearly too small to make a good omelet, most mosquito eggs will hatch into larvae within 48 hours. Solid proof of the durability of the mosquito is that their eggs have been know to withstand subzero winters before then hatching in the spring.
Once the eggs have hatched, the larvae live out their short existence in water and generally must come to the surface to breathe. The larvae of many mosquito species have a siphon tube for breathing (kind of like a tiny snorkel), while other species must lie parallel to the surface or attach to plants to get their air. The larvae feed on microorganisms and other organic matter found in the water. Depending on the temperature of the water, mosquito larvae generally live from four to 14 days.
After a few days of happy snorkeling, the larva transform into the pupae state which is a time of resting where the organism does not eat. After a couple of days spent leisurely relaxing in a water-filled tire, the pupae then transform into adult mosquitoes in a process that is similar to the metamorphosis a butterfly goes through when changing from a cocoon into an adult butterfly.
Once the transformation process is complete, the newly emerged adult mosquito rests on the surface of the water for a short time to dry itself and allow its body parts to harden. Then the debauchery begins. Adult mosquitoes like to live out their short lives in the fast lane, spending their time drinking and mating.
The actual length of the egg, larva, and pupa states depend on temperatures and the specific species' characteristics. Some go through a life cycle in 14 days at a temperature of 70 degrees Fahrenheit that would take only 10 days at 80 degrees.
Recognizing the role that temperature plays in mosquito breeding helps us anticipate how frequently treatment is needed for adequate mosquito control. While swimming larva may slowly develop into pupa and adults during the fall months…..in mid-summer a complete generation of adults may populate the environment much more rapidly.
Factoid: Only female mosquitoes require blood for protein. This "bloodmeal" commonly known as the "mosquito bite," can be served-up by a number of mammals or birds. When a mosquito bites a host it mixes some of its saliva with the host's blood to prevent clotting. It is this action that transmits diseases from host to mosquito and mosquito to host. Male mosquitoes do not bite as they feed on the nectar of flowers and other sugar sources.
Additional Resources
The Mosquito Circle of Life
www.dep.state.pa.us/dep/deputate/waterops/Redesign/WestNile/WastewaterControl.htm [2]
Water is Thicker Than Blood
It is a known fact that mosquitoes generally lay their eggs on fresh or stagnant water. A good mosquito nursery can consist of just about anything that will hold water for a short period of time including old cans, bird baths, ponds, and reservoirs. This is precisely the type of environment that can be found in and around just about every water and wastewater treatment facility.
Now for the good news, it is possible for systems to create an implement effective control strategies. Armed with a basic understanding of habitat and biology (what you have just finished reading) and under the direction of the EPA and your state primacy agency, every system can develop a sound plan by following a few simple steps.
Step 1: Planning: Begin by devising a plan that considers the extent of your problems and the resources needed to carry out the solution. As with any other good plan, you must combine education, monitoring, and inspection. You begin this process by identifying breeding sites, eliminating unnecessary standing water, and exploring any potential treatment options. Fortunately, there are several ways to potentially exploit the mosquitoes' own biology and behavior to help eliminate the problem without the use of pesticides or larvicides. Techniques such as agitation, aeration, and the elimination of unnecessary vegetation around ponds and reservoirs have been found to be effective. A good example of this is the use of a common garden sprinkler to disrupt surface water tension in stagnant areas.
Step 2: Organize: Every good program begins with a little bit of organization. People, funding, equipment, and planning are essential (However, giving your brother-in-law a fly-swatter and a couple of bucks to walk around your groundwater source and swat the little critters hardly qualifies). Once a plan has been established, the next logical step is to monitor populations and identify prime breeding sites. Monitoring larval and adult populations is essential to accurately estimate the need for, and the effectiveness of, control measures and to determine where you should concentrate your efforts.
Monitoring methods can include:
• Landing counts which record the number of adults that land on an unprotected arm over a certain period of time.
• Light traps that catch adult mosquitoes.
• Dip counts which record the average number of larvae and pupae located on the surface of a body of water.
Step 3: Reducing the breeding sites or larval habitats: Because water is the key element in mosquito development, managing standing water sites is essential. Reducing potential breeding sites can be as simple as clearing a blocked rain gutter, removing old tires, or as major as reworking landscaping and drainage in swampy areas.
Common sense is always the best practice when establishing an Integrated Pest Management Plan. Be sure to check with your local EPA office or state primacy agency before starting any treatment plan to ensure that you remain in compliance with all state and federal regulations. Remember, every state requires that larvicides, pesticides, and other chemical treatment options be approved and administered by a licensed applicator.
Additional Resources
EPA's Mosquito Control Page
www.epa.gov/pesticides/health/mosquitoes [3]
Swat 'Em If You Got 'Em
Large scale control of these annoying and sometimes dangerous insects has been the focus of extensive research resulting in three widely accepted approaches:
1. Eliminate breeding areas by various environmental modifications,
2. Application of chemicals to water surfaces to kill larvae or pupae,
3. The use of insecticides to kill adult mosquitoes.
A less common approach is to use natural predators of mosquitoes, either by adding a predator like the Mosquitofish to a water body or by modifying a habitat to enhance native predators like birds, bats, or other insects.
Since health and safety are critical elements of any water or wastewater system's plan, chemical applications should clearly be the method of last resort. Chemical treatment can be very costly, generally does not provide long term protection, and can be hazardous to both your customers and the environment.
While the use of any chemical means of controlling mosquito populations at or around drinking water treatment plants is generally prohibited, one of the primary larvicides used by wastewater treatment facilities is Bacillus thuriengiensis israelensis (BTI). Bti is a naturally occurring bacteria that does not interfere with the existing bacterial process occurring at a wastewater treatment plant. As with any treatment, larvicide should only be applied by a certified pesticide applicator.
Remember, while controlling mosquitoes may not be the most pressing item on your list of "things to do," it is an important part of being a good neighbor and protecting your customers. By taking a few precautionary steps now, you might just help prevent your neighbors from being infected by a disease carrying mosquito or from having any more pets carried off by hungry herds of "biting flies."