One Big Summer Fling

Saturday June 19, 2010


Mr Pest Control


I have a question about mosquitoes. The town I live in is considering having the entire town sprayed at once. Can you tell me the pros and cons of this, such as health issues, etc.? I am also looking for an alternative treatment to accomplish their goal. Any help would be greatly appreciated.

Mr Pest Control


Well, this gives me a chance to discuss mosquito management a bit. Let's begin with some of the positives about reducing populations of mosquitoes. These blood feeding insects are serious public health threats, and until West Nile Virus came along in the U.S. most people in this country couldn't tell you the names of any of the diseases mosquitoes vector, even though around the world today Malaria alone kills 2 to 3 million people each year. It's amazing how attitudes change when it's your own family getting sick from a mosquito-borne disease, and suddenly aerial spraying and street fogging were acceptable. WNV occurs throughout the U.S., so no region can say it could not possibly happen, and with our lawsuit-happy society in the U.S. the inevitable has already happened. People have sued public agencies because they contracted WNV, and blamed that agency for NOT having prevented it from happening by eliminating the mosquitoes. And, of course, those same public agencies get sued by people who claim health effects due to the pesticides being used for the mosquito control - you just can't please them all.

The active ingredient most often used for fogging for adult mosquitoes is pyrethrum - good old natural pyrethrum found in plants. Is it toxic? Well, certainly it is, but the relative toxicity to mammals is extremely low and the residual once applied is extremely short. However, it very effectively knocks down and kills any adult mosquitoes that it contacts in that short interval after being applied. But, it leaves no residual effect, so if breeding sources for the mosquitoes are not also being dealt with you will have another full crop of adult mosquitoes available again within a week or two. Fogging for adult mosquitoes gives wonderful temporary relief, but no lasting effect unless it is done regularly. A bit longer residual might be gained from another fogging ingredient, and that is permethrin, but again, this does not affect the larvae breeding in aquatic habitats. In your region of the Upper Midwest you could expect the mosquitoes to be breeding throughout the summer, so this current fogging would not give lasting results.

Could pyrethrum harm someone? While the reality is that it is highly unlikely anyone would suffer serious health consequences from exposure to pyrethrum, it also is the reality that many people will believe it is harming them, and they can make trouble. It also is very possible that some people would be hyper-sensitive to pyrethrum, and have allergic reactions to it just as they might to any plant oil. It would be unrealistic to expect EVERYONE in town to buy into the idea that this fogging is benign with respect to their health. We also have to recognize that pyrethrum is not going to kill ONLY mosquitoes, but will also kill a great many beneficial insects that are contacted by it. This kind of collateral damage is unfortunate, but sometimes may need to happen in a public health emergency. However, expect that criticism to occur.

As with so many pest management programs, ideally you control the source. In the case of mosquitoes this is standing water - ponds, marshes, swampy areas, backyard ponds and bird baths, slow flowing creeks, abandoned tires, buckets, bottles, plugged rain gutters, tarps on boats, abandoned pools, etc. A major effort at educating the residents should take place to enlighten them on how to eliminate all breeding sites on their own properties. You won't get them all, but if you get a lot of them it certainly reduces the overall problem. Then, for those sites that cannot be drained in some manner you should emphasize larval control, using one of the two main ingredients for mosquito larvae - the bacteria B.T.I. or the growth regulator Methoprene. These are essentially harmless to anything but mosquito larvae, and prevent them from developing to the biting adult stage. This kind of mosquito work is undoubtedly more expensive than just driving the fogging truck through town, but ultimately it actually gives mosquito control for a longer period of time.

Larval management is one alternative to fogging, although it does not kill biting adults, and so relief takes longer if only habitat applications are done. For killing large numbers of adult mosquitoes there are really no comparable alternatives to fogging. People are going to tell you to let the birds, bats, and dragonflies handle the job, but the fact is that Purple Martins and Bats have little impact on populations of mosquitoes, and any self respecting bat would rather eat one large flying moth than try to catch 500 tiny mosquitoes. Sometimes humans need to step in. Fogging is a very effective method for instantly giving relief from biting mosquitoes, and may be needed. But, hopefully the city also is well aware of the need to address the larval control, whether by eliminating breeding sites or treating those that must remain. This is where you can help to educate them.

Mr. Pest Control

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Please note, Mr. Pest Control is answering questions supplied by PMP customers across North America. His answers are generated from industry and manufacturer-provided information. The answer may not be specific to the laws and regulations for your State, Province, Territory or Country. In addition, products mentioned may not be registered and or available in all areas. Always check with your local Univar office for specific information to your area. Always read and follow label directions.