Mosquito Management on the St. Croix

In 1968, the St. Croix River became one of the first eight rivers protected under the Wild and Scenic Rivers Act. Under this act, rivers with "outstandingly remarkable scenic, recreational, geologic, fish and wildlife, historic, cultural, or other similar values" will be "preserved in free-flowing condition" so that humans can enjoy them in their natural state. However, humans who want to fish, camp, canoe, live near, or just enjoy the natural beauty of the St. Croix River are not so happy with the natural abundance of mosquitoes, which bite and spread disease. To get rid of mosquitoes, the MMCD, Metropolitan Mosquito Control District, puts three chemicals in the St. Croix River: methoprene, Bacillus thuingiensis (Bti), and pyrethrins. These three are toxic to mosquitoes, but are also toxic to various other aquatic life and thus can alter ecosystems.

How can humans balance their wants and needs with the ultimate goal of keeping the river wild and scenic?

Methoprene
Pyrethrins
Bti
The Problem with the treatments
Solutions
Our Beliefs

   Mosquito Lifecycle
   http://www.tetonmosquito.org/images/mosquito_life_cycle.jpg

Three Different Types of Pesticides

Methoprene: Is a general use pesticide that interferes with the maturation of mosquito larvae into adults via regulation of the insect's growth hormone. It has is in the toxicity class IV – slightly to practically nontoxic (general use pesticide) . Although it is slightly toxic to birds it is not lethal as it only causes incoordination and tiredness for a few days. Mammals experience little difficulty with Methoprene because they quickly break it down and excrete it. In the case of mosquitoes, Methoprene kills on contact.

Application of Methoprene Granules- http://pubs.caes.uga.edu/caespubs/pubcd/B1191/indiv2.jpg

Pyrethrins: Are considered restricted use pesticides. They are natural insecticides produced by chrysanthemums which are dried and powdered or the oils in the flowers are extracted with solvents. It works by affecting the nerve system of adult insects. Pyrethrins can cause breathing trouble, nausea and convulsions in humans. They are extremely toxic to aquatic life and can be broken down in sunlight and air. They are more toxic at higher water temperatures and acidity. Pyrethrins extracted from the flowers alone are not enough to kill the insects, only temporarily immobilize them. In order to ensure a lethal dose, the pyrethrin must be combined with organophosphates, carbanates, or synergists. Semisynthetic pyrethrins and pyrethroids have been found to be more effective.

Chrysanthemums used for pyrethrum production
http://www.btinternet.com/~micka.wffps/poisonous.html

Bti: Is a general use pesticide found in naturally occurring bacteria. It is a toxicity class III- slightly toxic which means it is practically nontoxic to fish but may adversely affect shrimp and mussels. Different strains are toxic to different types of insects (Bti – variety israelensis – is toxic to mosquitoes, blackflies, and some midges. Bti is ineffective against adult insects and works by inhibiting the maturation of insect larvae into pupa. It takes the form of little spores that multiply in the stomach of the larvae and stop them from feeding on host plants. They essentially starve to death and are unable to reach their adult stages as a result. Bti lasts 4 months in soil, 48 hours in water, and is destroyed by sunlight in under 4 hours. It breaks down rather easily in the environment because it is naturally occurring.

Forms of Bti
http://www.biconet.com/biocontrol/GIFs/bitsanddunks2.jpg

Here is a site for some prices on these products

The Problem with these Treatments

The Pesticides mentioned above are in fact effective at reducing mosquito populations but they bring with them a set of issues. Like bombs, these chemicals aren't entirely accurate and other members of the ecosystem shared by the mosquitoes can suffer the conequences. Everything in an ecosystem is linked to everything else in the same ecosystem and when one species is inadvertently killed or harmed in the process of removing mosquitoes, the effects can reverberate elsewhere.

Solutions

As one of the rivers classified as "wild and scenic," the St. Croix should theoretically be maintained in its natural state; we should leave the mosquitoes alone. However, the extent to which we try to maintain "wilderness" must be reconsidered when it comes to disease and comfort that play a role in life near the river. Here are three ways of approaching the situation.

Continue using pesticides to control mosquito populations
Leave mosquito control up to the people
Let mosquitoes bite and spread disease

Solutions	Positives	Negatives
Continue using pesticides to control mosquito populations	Effectively keep mosquito populations in check, thereby reducing the risk of disease and making activities near the river more pleasant	Detracts from the "wild" aspect of the St. Croix and can be detrimental to humans, animals, and the entire ecosystem
Leave mosquito control up to the people	There would be less of an impact on the ecosystem and humans would still be able to find some sort of protection from disease and discomfort	Over time there still may be an impact on the environment as different home-use pesticides begin to build up. This however would be minimal compared to current pesticide use.
Let mosquitoes bite and spread disease	This would carry out the very definition of a "wild" area. This is the way things were before human alteration to the environment	Obviously, disease is less than desirable. Taking humans out of the picture entirely could be letting mosquitoes become a dominant species

Our Beliefs

We believe in the spirit of the Wild and Scenic Rivers Act; mosquitoes should be left alone to preserve the St. Croix's natural-wild and scenic- state. Humans can deter mosquitoes on their end using inscect repellant and clothing with a lot of coverage. However, we recognize that health is a major concern. Should mosquito-spread disease become a significant problem, chemical intervention would be justified.

Compiled by: Shubha Singh, Laura Panfili, and Peter Walters

References:Metropolitan Mosquito Control District--- http://www.mmcd.org
Extension Toxicology Network---methoprene---bti---pyrethrins
EPA- Biopesticides fact sheet
Fish and Wildlife Service--Long term study on the effects of bti and methoprene