Mosquito Surveillance
Surveillance is a key component of an integrated mosquito management program. It is used to measure adult and larval mosquito populations, trigger control methods, determine the efficacy of control methods, and gather adult mosquitoes for arbovirus testing.
Adult mosquitoes are collected using CDC traps with three D-cell batteries that power a small fan and dim light bulb. Baited with dry ice, the traps release a carbon dioxide scent, which along with the dim light bulb attracts female mosquitoes. Once the mosquitoes are attracted to the trap, the small fan pulls them into the net and keeps them there until a technician retrieves the trap the following day. The traps are then taken back to the lab and trapped mosquitoes are counted and identified by species. Once collection data is tallied, appropriate action is taken based on the results. Mosquito traps are used only to monitor mosquito populations and are not known to be an effective tool for controlling mosquitoes.
Collecting adult mosquitoes can provide several important pieces of information. When traps are set at specific locations over a period of time, or in response to a service request, increases in mosquito populations can be detected. Once these mosquitoes are identified, control measures can then be more easily directed. Knowing what species of mosquito are present in a particular area can help vector control technicians find the larval production site and take the appropriate control measures. After identification by district employees, vector species of mosquitoes can also be tested for the presence of disease. The detection of virus in a mosquito, which may have come into contact with a human, horse, or bird, indicates a true potential for concern, and immediate control measures may be implemented. Trap collections not only determine where control measures are needed, but also determine the effectiveness of the control measures that are in place.
Larval Mosquito Control
Larviciding is the process of controlling mosquitoes when they are in the larval or pupal form. Although this is not the most visible part of the program, the majority of insecticide treatments performed by the WUMCD each year are larvacide treatments. Controlling mosquitoes when they are isolated in known breeding sites is often times the most effective approach to controlling populations of mosquitoes. The WUMCD uses several active ingredients in various formulations including: Bacillus thuringiensis israelensis (Bti), Bacillus sphaericus, Methoprene, Spinosad, and Larvicide Oil. All of these insecticides are approved for use by the EPA, Oregon Health Authority and the Oregon Department of Fish and Wildlife.
The district maintains a database that catalogs known larval sites. There are anywhere from 1,000 to 1,200 active sites at any time within the district boundaries. WUMCD has a crew of 4-6 people responsible for inspecting aquatic mosquito habitats and treating larvae and pupae when present using motorized backpack sprayers hand sprayers, and a drone. Inspection and treatment information is recorded in a computerized database. When large areas need larval treatment, the district utilizes an unmanned aerial vehicle (drone) for hard-to-reach areas and subcontracts with a local flying service to make large aerial treatments by helicopter.
Biological Controls
Biological Controls are the implementation of natural predators of mosquitoes to help reduce overall populations. Unfortunately, there are not many natural predators available that appear to work in mosquito control. Animals such as bats and small birds, like Purple Martins, are believed to eat large amounts of mosquitoes, but studies indicate that mosquitoes make up a very small portion, or even no portion, of their diets. Dragonflies appear to help in reducing numbers, but problems exist with using dragonflies as a control measure; their effectiveness has not been thoroughly studied, they have limited environments where they can survive, and rearing and distributing dragonfly populations is difficult and expensive.
Mosquitofish, or Gambusia, are small, darkly colored, guppy-looking fish that have voracious appetites for the larvae of mosquitoes. In certain areas they seem to be quite effective, but they are not 100% reliable and water sites where introduction is allowed are limited. Gambusia have shown to be quite effective for watering troughs and decorative ponds. West Umatilla has a permission to transport the fish (for the purpose of larval mosquito control) by the Oregon Department of Fish and Wildlife. Gambusia cannot be placed into or in any water connected natural waterways.
Adult Mosquito Control
Adult mosquito control or “fogging” is the most visible activity within the WUMCD’s IMM program but is often the last resort for the control of mosquito populations. The WUMCD’s primary method of adulticiding is four truck-based Ultra Low Volume (ULV) spray units applying either natural pyrethrins, or resmethrin. Aircraft is used as a secondary method of control generally only during large outbreaks of mosquitoes. As mosquito numbers reach a treatment threshold, the district will consider ULV applications to reduce adult mosquito populations. By reducing the numbers of mosquitoes, the likelihood of encountering adult mosquitoes diminish. More importantly, when disease is present, the likelihood for transmission is lowered.
Adulticiding must be done during a temperature inversion. During the mosquito season, temperature inversions typically occur at dawn and dusk. Therefore, applications are made early in the morning or in the evening while most people and non-target organisms are less active in treatment areas. Special considerations are taken when an adulticide application is to be made in highly populated areas. These considerations include product selection and application time. We choose the most effective and least offensive products available for these applications. Often times, highly reflective signs are placed at busy intersections to alert the public before an application, especially in areas that are not routinely treated. WUMCD annually contracts with a company specializing in aerial spraying.
Public Education
The West Umatilla Mosquito Control District recognizes the importance of Public Education in a modern mosquito control program. The district has made some improvements to its existing public education program over the past few mosquito seasons, the highlights being the addition of a public education trailer and a district mascot. These additions were funded, in large part with grant money secured from the Wildhorse Foundation, and the Echo Community Benefit Fund. The following are examples of the district’s public education efforts each year:
- The District’s web site – www.wumcd.org
- Public service announcements on all Umatilla County radio stations.
- The district has articles appear in the East Oregonian, Tri-City Herald, and the Hermiston Herald. These articles focused on mosquito control and district operations.
- District employees attend many health fairs, conventions, church functions, and the county fair. At these events, pamphlets and other educational and promotional items are given out to increase awareness about mosquitoes, the diseases that can be transmitted by mosquitoes, and how the district is working to control mosquitoes. Examples of events that you will find us attending are:Umatilla Landing Days, block parties, Stanfield 4th of July Parade, Umatilla County Fair Parade, Umatilla County Fair, Family Care Health Fair, Oregon State Fair, and Family Health & Fitness Day.
The WUMCD Staff are always willing to come and speak to service groups, chambers of commerce, church groups, and at school functions. Contact us at info@wumcd.org to schedule a presentation.
