Bacillus thuringiensis (B.t.).
Carrie Swadener. Journal of Pesticide Reform, Volume 14, Number 3,
Northwest Coalition for Alternatives to Pesticides, Eugene, OR.
Bacillus thuringiensis (B.t.)
by Carrie Swadener
Bacillus thuringiensis (B.t.) is a live microorganism that kills
certain insects and is used to kill unwanted insects in forests,
agriculture, and urban areas.
In a purified form, some of the proteins produced by B.t. are acutely
toxic to mammals. However, in their natural form, acute toxicity of
commonly-used B.t. varieties is limited to caterpillars, mosquito
larvae, and beetle larvae. B.t. is closely related to B. cereus, a
bacteria that causes food poisoning and to B. anthracis, the agent of
the disease anthrax. Few studies have been conducted on the chronic
health effects, carcinogenicity, or mutagenicity of B.t. People
exposed to B.t. have complained of respiratory, eye, and skin
irritation, and one corneal ulcer has occurred after direct contact
with a B.t. formulation. People also suffer from allergies to the
"inert" (secret) ingredients. People with compromised immune systems
may be particularly susceptible to B.t.
Viable B.t. spores are known to exist for up to one year following
application. Insect resistance to B.t. has been well documented.
Genetic engineering may greatly expand use of B.t., speeding up the
development of more resistance.
Large-scale applications of B.t. can have far-reaching ecological
impacts. B.t. can reduce dramatically the number and variety of moth
and butterfly species, which in turn impacts birds and mammals that
feed on caterpillars. In addition, a number of beneficial insects are
adversely impacted by B.t.
B.t. is less toxic to mammals and shows fewer environmental effects
than many synthetic insecticides. However, this is no reason to use
it indiscriminately. Its environmental and health effects as well as
those of all other alternatives must be thoroughly considered before
use. B.t. should be used only when necessary, and in the smallest
quantities possible. It should always be used as part of a
sustainable management program.
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