| Identification | Back Directory | [Name]
Bacillus thuringiensis | [CAS]
68038-71-1 | [Synonyms]
DIPEL
bactur
btb 202
agritol
Bacilex
bakthane
berliner
BIOTROL4K
bactospein
THURICIDE-HP
bitoksybacillin
thuringiensis sp.
BACILLUS THURINGENSIS
BACILLUS THURINGIENSIS
Bacillusdede thuringiensis
bacillus thuringiensis berliner
Bacillus thuringiensis suspension
Condor,Cutlass(Roussel-Uclaf Group)
Bactospeine(distributor,Biochem Products Ltd) | [EINECS(EC#)]
1806241-263-5 | [Molecular Formula]
C22H32N5O16P | [MDL Number]
MFCD01769457 |
| Hazard Information | Back Directory | [Chemical Properties]
Bacillus thuringiensis is commonly known as B.t. It is a microorganism that produces chem-
icals toxic to insects. B.t. was registered in the United States for use as a pesticide in 1961
and re-registered in 1998. B.t. occurs naturally in the environment and has been isolated
from soil, insects, and plant surfaces. B.t. pesticides are used for food and non-food crops, greenhouses, forests, and outdoor home use. B.t. pesticides exist in granular, powder, dust,
suspension, and l owable forms.
A number of insecticides are based on these toxins. B.t. is considered ideal for pest man-
agement because of its specii city to pests and because of its lack of toxicity to humans
as well as natural enemies of many crop pests. There are different strains of B.t., each
with specii c toxicity to particular types of insects. For instance, B.t. aizawai (B.t.a.) is used
against wax moth larvae in honeycombs, B.t. israelensis (B.t.i.) is effective against mos-
quitoes, blackl ies and some midges, and B.t. kurstaki (B.t.k.) controls various types of
lepidopterous insects, including the gypsy moth and cabbage looper. A new strain, B.t.
san diego, has been found to be effective against certain beetle species and the boll weevil.
In order to be effective, B.t. must be eaten by insects in the immature, feeding stage of
larvae development. B.t. is ineffective against adult insects. Regular monitoring of the
target insect population before application of B.t. ensures good control of the vulnerable
larval stage. More than 150 insects, mostly lepidopterous larvae, are known to be suscep-
tible in some way to B.t. Death of target larvae is known to occur within a few hours to a
few weeks of B.t. application, depending on the species of insect and the amount of B.t.
ingested by the insect.
B.t. is moderately persistent in soil and its toxins degrade rapidly. The movement of B.t.
is limited following pesticide application and it is unlikely to contaminate groundwater.
B.t. is not native to water and is not likely to multiply in water. | [Health Hazard]
The insecticidal action of B.t. is attributed to protein crystals produced by the bacte-
rium. Exposures of test animals to B.t. using several routes did not produce any acute
toxicity in birds, dogs, guinea pigs, mice, or rats. Also laboratory rats when injected
with B.t.k., showed no toxic or virus-like effects. No oral toxicity was found in rats,
mice, or Japanese quail fed protein crystals from B.t. var. israelensis. Studies indicated
that after rats ate B.t., the microorganism remained in the digestive system until it was
eliminated from the body. Rabbits exposed to B.t. showed mild skin irritation and rats
showed low inhalation toxicity to B.t. In fact, chronic toxicity studies in dogs, guinea
pigs, rats, and other species of test animals showed no evidence of adverse health
effects.
The toxicity of B.t. is insect specii c. Researches have provided valuable data and
identii ed B.t. subspecies that differ in toxicity to different insects. Examples of B.t.
subspecies and the insects they affect are aizawai (moths), kurstaki (moths), israelen-
sis (mosquitoes and l ies), and tenebrionis (beetles). Also, phytotoxicity studies (plant
researches) showed B.t. genes in some crops (B.t. crops) to combat insects of corn crops,
cotton, and potatoes. B.t. must be eaten by insects to be effective and works by interfer-
ing with digestion. Insects are most sensitive to B.t. when they are larvae, an immature
life stage. Insects that eat B.t., die from hunger or infection. It does not cause disease
outbreaks in insect populations. B.t. may produce toxic chemicals that are released from
the organism | [Description]
Bacillus thuringiensis is the most widely known
and researched bacterium within this group and is
differentiated from other spore-forming bacilli by the
presence of a parasporal body that is formed within
the sporangium during sporogenesis. The parasporal
body is a high-molecular-mass protein crystal that is
referred to as crystalline protein, δ-endotoxin, as well as
a parasporal body. This protein moiety possesses some of
the insecticidal properties of the bacterium (26). | [History]
Bacillus thuringiensis subspecies israelensis was isolated
from a mosquito breeding site in Israel (33). The
discovery of this subspecies provided researchers with an
isolate with consistently high toxicity against larvae of
mosquitoes and blackflies (order Diptera). All other subspecies
are predominantly toxic for larvae of Lepidoptera.
This subspecies also contains a parasporal crystal protein.
However, this crystal is irregular in size and instead of
a single crystal, there are 3–5 crystals. The pathology
caused by subspecies israelensis is similar to that of other
subspecies of B. thuringiensis in susceptible Lepidoptera.
The pathology in black flies is most likely very similar.
Bacillus thuringiensis subspecies israelensis is also
produced by submerged culture. | [Uses]
Bt has been used in spray formulations for more than 40 years,
and more recently its insecticidal protein genes have been
incorporated into several major crops. Due to their insecticidal
activity, Cry toxins are used worldwide as bioinsecticides to
control disease-vector insect and crop pest populations.
One of the most successful applications of Bt has been the
control of lepidopteran defoliators, which are pests of coniferous
forests mainly in Canada and the United States. Bt subsp.
israelensis (Bti) is highly active against larvae of disease-vector
mosquitoes like Aedes aegypti (vector of dengue fever), Aedes
albopictus (vector of chikungunya), Simulium damnosum (vector
of onchocerciasis), and certain Anopheles species (vectors of
malaria). Bti formulations (WG, water-dispersible granule;
DT, ready-to-use tablet) have been evaluated by the World
Health Organization Pesticide Evaluation Scheme (WHOPES)
and recommended as mosquito larvicides, including their
use against mosquito larvae that develop in drinking-water
containers. Successful application of Bt is highly dependent
on proper timing, weather conditions, and dosage of spray
applications. These factors combine to determine the probability
of larvae ingesting a lethal dose.
Recently, the use of Cry toxins has increased dramatically
following the introduction of cry genes into plants. These
‘Bt crops’ have thus far proved to be an effective control
strategy, and in 2004 Bt-maize and Bt-cotton were grown on
22.4 million hectares worldwide. Such widespread use,
however, has led to concerns about the effect Bt crops may have
on the environment and on human health. | [Biological Functions]
These early experiments showed that Bt toxins needed to be activated in the gut, and it was soon discovered that the critical factors were an alkaline environment and the presence of specific proteases, which cleaved the innocuous protoxin into its active form. Once activated by proteolysis, each toxin binds to receptors in the brush border membrane and causes pores to open, disrupting them ovement of solutes across the gut epithelium and causing the influx of water. The toxins were shown to be orally lethal to caterpillars in pure form, and the pro-toxins could be converted into active toxinsin vitro, using specific pro-teases under alkaline conditions. The requirement for alkaline conditions, specific proteases and specific receptors explains why Bt is harmless to mammals (which have anacidic gut and lack the corresponding receptors) and why each toxin has a narrow host range.
Nine common pests of rice, cotton and maize that are controlled by Bt crops | [Agricultural Uses]
Bacillus thuringiensis (Bt) is an important insect
pathogenic bacterium commercially known as
'Thuricide' It releases toxic polypeptide crystals which
are degradable by the enzyme, protease. The bacterium is
pathogenic to the following insects: Lepidoptera, Diptera
and Coleoptera.
Bacillus thuringiensis has been exploited
commercially and its sprays have been used in the USA
since the 1930s. It is the only commercialized transgene.
The Bt toxin provides resistance against insects by
binding to specific sites in the insect gut. However, insect
resistance to Bt is also known. | [Safety Profile]
Low toxicity by ingestion and skincontact. When heated to decomposition it emits acridsmoke and irritating vapors. | [Environmental Fate]
Bt Cry and Cyt toxins belong to a class of bacterial toxins
known as pore-forming toxins (PFT) that are secreted as watersoluble
proteins undergoing conformational changes in order
to insert into, or to translocate across, cell membranes of their
host. The primary action of Cry toxins is to lyse midgut
epithelial cells in the target insect by forming pores in the apical
microvilli membrane of the cells.
Bt is ineffective against adult insects and must be eaten by
feeding larvae in order to be toxic. When ingested by insect
larvae, sporulated-Bt crystalline inclusions dissolve in the
alkaline environment of insect gut, and the solubilized inactive
protoxins are converted into protease resistant active Cry
and Cyt toxins. Toxin activation involves N-terminal, Cterminal,
and intra-molecular cleavage. The activated Cry
toxins are composed of three functional domains, a seven ahelices
bundle that is involved in membrane insertion
(domain I), and two b-sheet domains (domains II and III)
involved in receptor interactions. Once activated,
Cry toxins bind to specific receptors on the brush border
membrane of the midgut epithelium columnar cells before inserting into the membrane. Toxin insertion leads to the
formation of lytic pores in microvilli of apical membranes.
Subsequently cell lysis and disruption of the midgut epithelium
release the cell content providing the spores with
a germinating medium leading to a severe septicemia and
insect death. | [Toxicity evaluation]
Bt is moderately persistent in soil with a half-life of ca. 4 months.
Bt subsp. israelensis is often applied directly to water for the
control of mosquitoes and blackflies. It has been demonstrated
that the sedimentation of Bti is facilitated by adsorption onto
particulate material. Bti can persist as long as 5 months in cold
water, and adsorption to particulate matter in water facilitates
persistence.
Bt is relatively short-lived on foliage due to rapid photodegradation.
Its half-life under normal sunlight conditions is
3.8 h. In general, Bt loses 50% of its insecticide activity in 1-3
days after spraying. However, high toxicity toward mosquito
larvae has been found in decaying leaf litter collected in several
natural mosquito breeding sites in forested areas. From the
toxic fraction of the leaf litter, B. cereus-like bacteria were isolated
and further characterized as Bt subsp. israelensis using PCR
(polymerase chain reaction) amplification of specific toxin
genes. The anthropogenic origin of Bti was demonstrated by amplified fragment length polymorphism (AFLP) profile
comparisons. Nevertheless, persistence of acute toxicity several
months after Bti spraying remains exceptional, as this was only
observed once in only one out of eight sampling sites. In this
particular site, Bti spores and toxins may be protected from
degradation by the vegetal matrix. |
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