RECOMMENDATIONS FOR MOSQUITO CONTROL PROGRAMS. Kristy Gottfried, Medical Entomologist

To view the entire article:  http://www.beyondpesticides.org/mosquito/documents/Nashville%20advice%20TNDOHCountyDirsMtngGottfriedvm.pdf

Adulticiding as the only control source is ineffective for the following reasons:

1. There are approximately 170 different mosquito species found in the US and approximately 50 mosquito species found in Tennessee. All mosquito species found in Tennessee are not pests nor do they feed on humans nor are they WNV vectors. Even though there is a list of mosquito species that have been found with evidence of WNV contact in the US, very few of those species are biologically capable of serving as effective WNV vector species.

There are three primary mosquito species in Tennessee that are involved in WNV transmission to humans and are all in one genus: Culex. If a program is designed specifically to reduce the mosquitoes that are involved in WNV transmission, then the program must be specific and targeted for the mosquitoes in the genus Culex. I say this to convey the critical point that an effective program must specifically target the species present in the area. Since, eradicating mosquitoes is not possible, an acceptable level of mosquitoes must be determined. Once the mosquito species are identified, the knowledge of flight, biting and breeding behavior will allow the program to apply adulticides effectively. The bottom line is that the application of adulticides without regular mosquito surveillance (knowledge of the target species) may look pleasing to the average citizen, however, it is ineffective and can potentially lead to serious consequences.

2. Adulticides are designed to break down fast in the environment; there are NO residual effects of the product. Product droplets that land and dry on surfaces will not kill mosquitoes landing on that surface. Adulticides must come in direct contact with a flying mosquito to kill; mosquitoes that are in inaccessible habitats will not be affected. The appropriate timing of the adulticidal application is based on knowing the mosquito species present in the area as well as the behavioral (feeding, breeding) characteristics.

3. Adulticides will only kill flying adult mosquitoes that are in the area at the time of application and may supply short-term relief (3-4 days). The immature stage (larvae) found in water sources will NOT be affected. When the next generation of mosquitoes emerges from the water surfaces, there is an entire new population that will need to be treated. In addition, some mosquito species are capable of flying long distances in search of a blood meal; treatment in one area will not prevent searching mosquitoes from another area entering the treatment area after application.

4. Overuse and non-regulated use of chemical products used for adulticiding or larviciding have the potential to increase the resistant individuals in a population. Once resistant individuals increase in a resident mosquito population, killing the adults becomes increasingly difficult. Resistance occurs when a mosquito population is treated with a chemical product and although a substantial proportion may die, there will be a few that have the capability of reducing the chemical to inert compounds with no biological effects. Survivors will be capable of passing on these favorable genetic characteristics to their progeny and essentially an artificial selection process will produce a resistant population.

Since adulticidal products are expensive, the natural thought would be to most operators to decrease the concentration for the purpose of reducing cost. This is a great mistake and actually results in encouraging the development of a resistance mosquito population. The application of less concentrated products will not provide a lethal dose and will result in a mosquito population with resistant individuals. Resistant individuals will build up in a population with each additional application of decreased concentration. There are very few EPA registered adulticidal products on the commercial market. Promoting resistant populations in a region will only decrease the effectiveness of these few products. Then during an unfortunate time if/when a critical public health situation arises, the products of choice will be limited and success questionable.

5. There are non-chemical strategies available for use in many situations and the EPA recommends considering using these methods as part of an overall pest management strategy, IPM. Therefore, adulticides should play only a small roll in the overall mosquito control program.

IF A REGION IS GOING TO INVEST LOCAL FUNDS INTO A MOSQUITO ABATEMENT PROGRAM-THEN THE PROGRAM SHOULD BE FUNDED SUFFICIENTLY TO ENSURE COMPLIANCE WITH PROFFESSIONALLY ACCEPTED MOSQUITO CONTOL STANDARDS.