Bt, or Bacillus thuringiensis, has been used in some form or another for almost half a century as a specific pesticide against various insects. For some years, it has been one of the most effective pesticides organic growers can use. Bt is a natural organism found at low levels in soils throughout the world. It works by secreting one or more toxins after being ingested by an insect. The toxins are often specific to a family of insects. It appears not to harm humans or other life forms except for the intended targets.
It’s natural, it’s selective. So, what’s the problem?
Increasingly, the types of Bt being used are rare strains that are performance-enhanced or sometimes genetically engineered. The use of Bt pesticides has spread from farms and occasional homeowner use to the spraying of millions of acres every year around the world, often over large tracts of forest land or areas with large urban populations.
The Bt strains being used are applied at rates up to one billion times the natural levels. Often, they wipe out entire families of insects in the sprayed areas. For instance, Btk, a strain used to control moth pests such as tussock and gypsy moth, kills all insects in the Lepidoptera family (moths and butterflies). Soil biota is also affected – there is evidence to show that nematodes and predator insects (that would naturally control the pest population) are depressed also.
Despite Bt’s purported safety for humans, no long term testing has ever been done to assure its safety. Why should you worry?
- Bt is extremely similar (so much so it is difficult to distinguish without sophisticated testing) to two other bacteria, B. cereus, which causes food poisoning, and B. anthracis, which causes anthrax.
- Bt secretes many of the same toxins B. cereus does when it is growing. There is mounting evidence that spores germinate in humans and can live for extended periods of time in the respiratory and gastrointestinal tract. The effect of these low level infections is unknown, but there have been isolated reports of disease caused by Bt. One of the reasons Bt may not be seen as a common cause of sickness is that it is very hard to test for its presence – many cases diagnosed as B. cereus gastroenteritis (a fairly common form of food poisoning) may in fact be caused by Bt.
- People with sensitive immune systems could be affected in ways we do not yet know, but immune responses are seen when humans come into contact with Bt.
- DDT was used for thirty years and was claimed to be extremely safe for humans. The same sort of testing done to arrive at that conclusion has been done with Bt.
- Unfortunately, when Bt pesticides are formulated, a number of “inert” ingredients are added as preservatives, enhancers, and flow and wetting agents. These inerts are never revealed by manufacturers or tested for safety, and some may be toxic. For instance, Foray 48B, a common moth insecticide, probably contains the chemical BIT (1,2-benzisothiazolin-3-one) that was recently prohibited for environmental releases in the EU.
Like it or not, we are all part of a big experiment now, as the world’s agricultural and timber industries increasingly rely on applications of different Bt strains to more and more land and estuarine areas. Attempts to moderate the amount of spraying by activist groups throughout the world are met with the unified opposition of drug and pesticide companies and agribusiness.
In the US alone, well in excess of one million acres per year are treated with Btk and Bti pesticides to control gypsy moth, tussock moth, and mosquitoes. Often these applications are in cities or suburban areas. Aerial and ground applications supply more Bt spores in a single breath to inhabitants than they would get by eating a year’s worth of unwashed organic produce. Bt spores infiltrate effectively into closed homes and remain at high concentrations in the air for days after a single spraying.
The wholesale use of Bt pesticides and Bt toxin GM crops (a whole other topic) will also endanger Bt’s use in organic farming, because insects may eventually develop resistance to the natural Bt toxins. This will force growers to use genetically modified and untested (and more expensive) Bt’s.