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S

everal of our town councils are talking about a programme to spray a biodegradable, non-toxic organic substance which could eliminate 90% of the mosquitoes and black flies. Even though we are heading towards winter, it is probably the time to learn more about it, since decisions will be taken soon to start spraying in the spring. We contacted both the company, GDG Environnement Ltée and the Ministry of the Environment and we learned the following:

The insecticide used in the spraying is a biological pesticide called Bacillus Thuringiensis. It has been used in many forms in agriculture and tree farming and one variety (Kurstaki) was used on the spruce budworm a number of years ago. The variety used against mosquitoes and black flies is called Israelensis, or BT 14. It has been in use for years in other parts of the world, including Western Canada and the Adirondacks. In a copy of one study sent to us by the Ministry, 12 product names and 128 studies are listed. Repeatedly the research says that the pesticide is harmful only to the larval stage of the target species. It says that there is no effect on the food chain, since the creatures that feed on these larvae are not dependant on them as their sole food. No reduction is detected among their predators where the pesticide has been used, and the dead larvae are just as nutritious and non-toxic as the live ones. The pesticide, being a bacterium, is biodegradable and has no side effects on other species. While there is some evidence that the larvae develop a resistance to BT 14 over time, this resistance seems to disappear when the BT 14 is discontinued and the larvae intermix with unaffected larvae. Further, it is believed to be unlikely that resistance will develop if the pesticide is used in a controlled manner.

It sounds like a wonderful solution to our annual bug problem. It doesn't disrupt the food chain, it doesn't have toxic by-products, it only attacks the target species and it eliminates up to 90% of them. A welcome find, it would seem, for an area whose economy depends on recreational activity, but is there a downside?

Exposure to it does generate antibodies and it is recommended that exposure should be avoided if you have an autoimmune deficiency. While there is no evidence that it contaminates groundwater or waterways, both the Canadian and United States governments forbid its usage around drinking water. It is even recommended that no water be drawn from a reservoir during a spraying programme.

There is a warning in the notice prepared for Health and Social Services and for the Public Health offices, dated June 1995, that despite the large numbers of studies done, there is still not enough known about the consequences of playing around in our environment. It says that, while mosquitoes do pose a mild risk to our health, it is minor and does not justify intervention. It goes on to say that viral encephalitis is an example of a disease carried by mosquitoes that can be very easily controlled with BT 14, should the need arise, and that it would be tragic if misuse or overuse were to render this substance ineffective by the time we really need it.

It would appear that there is little risk to our environment in using this wonderful stuff. Then again, there is none involved in not using it. Of course our track record in estimating environmental risks isn't very good. It will be interesting to see what decision we make in our area. Each of us has a say. We only have to contact our municipal council and express our opinions.

References: Le bacillus thuringiensis israelensis et le contrôle des insectes piqueurs au Québec, mars 1994
Avis de santé publique sur l'utilisation du pesticide biologique bacillus thuringiensis en milieu forestier, agricole et urbain, juin 1995
L'insecticide bacillus thuringiensis et la santé publique, avril 1996

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