7898

• UCREFRP Catalog Number: 7898
• Author: Swadener, C.
• Title: Insecticide Fact Sheet,
• USFW Year: 1994
• Copyright Material: YES

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.JOURNAL OF PESTICIDE REFORM/ FALL 1994. VOL.14, NO.3

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. INSECTICIDE FACT SHEET

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BACILLUS 1HURINGIENSIS (B.T.)

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Bacillus thuringiens;s (B.t.) Is a live microOrganism that kills certain insects and is used to kill,
unwanted insects in forests, agriculture, and'urban areas. ' ,

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In a pwlfiedfonn, some of the proteins produced by B.t. are acutely toxic to mammals. However, in
their natural fonn, acute toxicity of commonly-used B.t. varieties is limited to caterpillars, mosquito
larvae, and Iieetle larvae. B.t. is closely related to B. cereus, a bacteria that causes food poisoning and
to B. anfhracis, 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 comeal ulcer has occurred after direct contact with a B.t.
fonnulation. People also suffer from allergies to the "inert" (Secret) ingredients. People with
compromi~ immunesysterns may be particularly susceptible to B.ti}~,:;: '
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Viable B.t. spores are known to exist for up to one ye';r follo~i~g 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.i r, , . "
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Large-scale applications of B~t. can have faf,;,reaching ecological impacts. B.t. can reduce dramatically
the number and variety of moth and butterfly species, which in tum impacts birds and mammals that
feed on caterpillars. II' addition, ~ number of b8nefic~al insects are adverSely impacted by B.t.
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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 altemativesmust 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. ' .'

BY CAluuE SWADEl'.'ER

A hazards of conventional, broad
acting pesticides are documented, research-.
ers look for pesticides t.h.at are are toxic only ,
to the target pest, have less impact on other
species, and have fewer environmental haz-
ards. BaciOus thuringiensis(B.t.) insecticides
result from this research. However, there is
evidence suggesting that B.t. is not as be-
nign as the manufacturers would like us to
believe, and that care is warranted in its
use.
B.t. is a species of bacteria that has in-
secticidal properties affecting a selective
range of insect orders. There are at least 34
subspecies of B.t. I (also called serotypes or

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C.rrle Sw.dener is NeAP's information services
coordinator.

vari~ti~) ~d probably over 800 strai~iso-
lares.2 B.t. was first isolated in 1901 in Ja-
pan from diseased silkworm larvae. It was
later isolated from Mediterranean flour
moths and named Bacillus thuringiensis in
1911.3 It was not until 1958 that B.t. was
used commercially in the United States.4
By 1989, B.t. products had captured 90-95
per cent of the biopesticide market.5
Bacillus thuringiensis products available in
the United States are comprised of one of
five varierl~ of B.t.: B.t. var. kurstaki and
var. morrison~ which cause disease' in moth
and butterfly caterpillars; B.t. var. israelensis
which causes disease in mosquito and
blackfly larvae; B.t. var. aizawai which
causes disease in wax moth caterpillars); and
B.t. var. tenebrionis, also called var. san diego,
which causes disease in beetle larvae.6,7
Other strains of B.t. have been discovered
that exhibit pesticidal activity against nema-
todes, mites, flatworms, and protozoa.5

B.t. produces aCe used to control moth
pests in fruits, vegetables, and beehives;
blackfly and mosquito pests in ponds and
lakes; and several beetle pests in vegetables
and shade rrees.6 (See Fig. 1,2, and 3 for
more details.) Common brand names in-
clude Dipel, Foray, Thuricide (all B.t.
kurstak,) , Veaobac, Mosquito Attack (all
B.t. israelensis), and M-Trak (B.t.
tenebrionis).6

Mode of Action

When conditions for bacterial growth
are not optimal B.t., like many bacteria,
forms spores. Spores are the dormant stage
of the bacterial life cycle, when the organ-
ism waits for better growing condinons.
Unlike many other bacteria, when B.t. cre-
ares spores it also' creates a protein c:rysral
This crystal is the toxic component ofB.t..
After the insect ingests B.t., the crystal is
dissolved in the insect's alkaline gut. Then

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