E X T O X N E T
Extension Toxicology Network
A Pesticide Information Project of Cooperative Extension Offices of
Cornell University, Michigan State University, Oregon State University, and
University of California at Davis. Major support and funding was provided
by the USDA/Extension Service/National Agricultural Pesticide Impact
Assessment Program.
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Pesticide
Information
Profile
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Bacillus Thuringiensis
Publication Date: 5/94
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TRADE OR OTHER NAMES
Berliner (B.t. variety kurstaki): Dipel, Thuricide, Bactospeine,
Leptox, Novabac, Victory. Certan (B.t. variety aizawa). Teknar (B.t.
variety israelensis).
REGULATORY STATUS
This microbial insecticide was originally registered in 1961 as a
general use insecticide. A registration standard, issued in 1986 by the
U.S. Environmental Protection Agency (EPA), required manufacturers to make
minor changes in label precautions and to provide additional data on the
effects of B.t. on nontarget organisms. While EPA considers the
toxicological data base for B.t. complete, the Agency is still requiring
more ecological effects data. Check with specific state regulations for
local restrictions which may apply.
INTRODUCTION
Bacillus thuringiensis (B.t.) is a naturally-occurring soil bacterium
that produces poisons which cause disease in insects. A number of
insecticides are based on these toxins (8). B.t. is considered ideal for
pest management because of its specificity to pests and because of its lack
of toxicity to humans or the natural enemies of many crop pests (14).
There are different strains of B.t., each with specific toxicity to
particular types of insects: B.t. aizawai (B.t.a.) is used against wax
moth larvae in honeycombs; B.t. israelensis (B.t.i.) is effective against
mosquitoes, blackflies and some midges; 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 development referred to as larvae. It is ineffective against adult
insects. Monitoring the target insect population before application
insures that insects are in the vulnerable larval stage (9). More than 150
insects, mostly lepidopterous larvae, are known to be susceptible in some
way to B.t. (5).
Bacteria are primitive one-celled organisms, which belong to a group
of organisms called prokaryotes. Prokaryotes are neither plants nor
animals. Like certain members of the plant kingdom, such as ferns and
mushrooms, B. t. forms asexual reproductive cells, called spores, which
enable it to survive in adverse conditions. During the process of spore
formation, B.t. also produces unique crystalline bodies as a companion
product. The spores and crystals of B.t. must be eaten before they can act
as poisons in the target insects. B.t. is therefore referred to as a
stomach poison (7). B.t. crystals dissolve in response to intestinal
conditions of susceptible insect larvae. This paralyzes the cells in the
gut, interfering with normal digestion and triggering the insect to stop
feeding on host plants. B.t. spores can then invade other insect tissue,
multiplying in the insect's blood, until the insect dies. Death can occur
within a few hours to a few weeks of B.t. application, depending on the
insect species and the amount of B.t. ingested (7, 13).
TOXICOLOGICAL EFFECTS
ACUTE TOXICITY
No complaints were made after eighteen humans ate one gram (g) of
commercial B.t. preparation daily for five days, on alternate days. Some
inhaled 100 milligrams (mg) of the powder daily, in addition to the dietary
dosage (6). Humans who ate one g/day of B.t.k. for three consecutive days
were not poisoned or infected (12).
Since it was one of the first biological control agents registered for
use against insects in the U.S., B.t. had to undergo a testing program
which was more thorough than that which the EPA currently requires for
biological pesticides. As a result, there are no data gaps in the toxicity
information required by the EPA for registration purposes. A wide range of
studies have been conducted on test animals, using several routes of
exposure. (The highest dose tested was 6.7 x 10 to the 11th spores per
animal.) The results of these tests suggest that the use of B.t. products
can cause few, if any, negative effects. B.t. did not have acute toxicity
in other tests conducted on birds, dogs, guinea pigs, mice, rats, humans,
or other animals. When rats were injected with B.t.k., no toxic or virus-
like effects were seen. No oral toxicity was found in rats, mice or
Japanese quail fed protein crystals from B.t. var. israelensis (19).
Very slight irritation was observed in test animals from inhalation
and dermal exposure. This may have been caused by the physical rather than
the biological properties of the B.t. formulation tested (14). Mice
survived one or more 1-hour periods of breathing mist that contained as
many as 6.0 x 10 to the 10th spores of B.t. per cubic meter (m3) (6). No
toxic effects were observed in rats that had a B.t. formulation put
directly into their lungs, at rates of 5 mg/kg of body weight (1).
The amount of formulated insecticide that killed 50% of the rats
experimentally fed the material ranges from 2.65 to greater than five grams
per kilogram (g/kg) (1, 12). This amount is referred to as the lethal dose
fifty (LD50) for B.t. in rats. Single oral dosages of up to 10,000
milligram per kilogram (mg/kg) of body weight did not produce toxicity in
mice, rats or dogs (1).
The dermal LD50 for a formulated B.t. product in rabbits was 6,280
mg/kg. Some reversible abnormal redness of the skin was observed when 1
mg/kg/day of formulated B.t. product was put on scratched skin for 21 days.
No general, systemic poisoning was observed. A single dermal application
of 7.2 g/kg of B.t. was not toxic to rabbits (1).
B.t. crystals have caused deaths in test animals when they were
injected directly into the abdominal cavity. This suggests that B.t. can
be toxic to mammals, but that when exposure is through normal routes of
exposure (oral, dermal or inhalation), metabolism or elimination of the
toxin prevents poisoning in mammals (19).
CHRONIC TOXICITY
No complaints were made by eight men after they were exposed for seven
months to fermentation broth, moist bacterial cakes, waste materials, and
final powder created during the commercial production of B.t. (6).
There is no evidence of chronic B.t. toxicity in dogs, guinea pigs,
rats, humans or other test animals. Thirteen-week dietary administration
of B.t. to rats at dosages of 8,400 mg/kg did not produce toxic effects
(14).
Reproductive Effects
This literature review did not produce any information on the effects
of B.t. exposure to reproductive systems.
Teratogenic Effects
There is no evidence indicating that formulated B.t. can cause birth
defects in mammals (1).
Mutagenic Effects
B. thuringiensis appears to have mutagenic potential in plant tissue.
Extensive use of B.t. on food plants might be hazardous, given its
mutagenic potential (6).
Carcinogenic Effects
Tumor-producing effects were not seen in two-year chronic studies
during which rats were given dietary doses of 8,400 mg/kg of B.t.
formulation (1).
Organ Toxicity
No additional information was found on the harmful effects of B.t. to
organs.
Fate in Humans and Animals
While B.t. interferes with insect digestion, it does not persist in
the digestive systems of mammals that ingest it. When placed in the eyes
of rabbits, Bt var. israelensis was still present after 1 week, but there
was no infection or other harmful effect to the eye. When injected into
the gut of mice, Bt var. israelensis was detected in the spleen and heart
blood for as long as 80 days, but there were no infections (16).
ECOLOGICAL EFFECTS
Effects on Birds
B.t. is not toxic to birds (2, 15). It biodegrades and does not
persist in the digestive systems of birds (9). The LD50 for bobwhite quail
was greater than 10,000 mg of B.t. per kg body weight. When autopsies
were performed on these birds, no pathology was attributed to B.t. Field
observations of 74 bird species did not reveal any population changes after
aerial spraying of the B.t. formulation (1).
Effects on Aquatic Organisms
B.t. has not been reported as having harmful effects in fish (2).
Rainbow trout and bluegills exposed for 96 hours to B.t. technical
material, at concentrations of 560 and 1,000 parts per million (ppm), did
not show adverse effects. A small marine fish (Anguilla anguilla) was not
negatively affected by exposure to 1,000-2,000 times the level of B.t.
expected during spray programs. Field observations of populations of brook
trout, common white suckers and smallmouth bass did not reveal adverse
effects one month after aerial application of the B.t. formulation (1).
Effects on Other Animals (Nontarget species)
Applications of labeled rates of formulated B.t. have not been toxic
to beneficial or predator insects (1). Treatment of honeycombs with B.t.
var. aizawai will not have a detrimental effect upon bees, nor on the honey
produced (4). Normal exposure rates do not cause harm to honey bees. Very
high concentrations (108 spores/ ml sucrose syrup) of B.t. var.
tenebrionis, which is used against beetles such as the Colorado potato
beetle, reduced longevity of honey bee adults but did not cause disease
(17).
As of 1986, EPA had not completed its assessment of the potential
impact of certain uses of B.t. on endangered and/or threatened species of
moths and butterflies. Concern was expressed regarding its potential to
kill endangered species of butterflies, along with target pests (9).
Users of B.t. are encouraged to consult local officials or the nearest
EPA regional office responsible for protecting endangered species before
using B.t. products in counties where susceptible endangered species of
Lepidoptera are known to be present. (In California: Los Angeles, Contra
Costa, Mendocino, San Francisco, San Mateo, Monterey, and Kern Counties; in
Florida: Date and Monroe Counties; in Washington: Pacific and Tillamook
Counties; and Lane County in Oregon) (12). Death occurs in some nontarget
insect species when B.t. is applied at rates used for mosquito control.
Results of other experimental testing do not suggest that B.t. adversely
affects nontarget insects or aquatic invertebrates. It did not have
negative effects on frogs and salamanders (2).
ENVIRONMENTAL FATE
B.t. is a naturally-occurring pathogen that readily breaks down in the
environment. As a biological entity, it is subject to death and
inactivation in the same fashion as all living things (1, 5). B.t. is
degraded very rapidly when exposed to UV light. Its half-life under normal
sunlit conditions is 3.8 hours. Formulations of B.t. spores and crystals
encapsulated in starch lost all spore viability and insecticidal activity
within 4 days (18). Due to its short biological half-life and its
specificity, B.t. is less likely than other chemical pesticides to cause
field resistance in target insects. In enclosed situations, however, B.t.
resistance has been reported in a stored grain pest, the Indian meal moth
(9). Because this material readily biodegrades in the environment, it
poses little or no disposal problem (11).
Breakdown of Chemical in Soil and Groundwater
Under suitable conditions, B.t. can persist for several months in
soil. Its spores are released into the soil from decomposing dead insects
after they have been killed by the bacterium. B.t. is rapidly inactivated
in soils that have a pH below 5.1 (1, 5).
Microbial pesticides such as B.t. are classified as immobile because
they do not move, or leach, with groundwater. Because of their rapid
biological breakdown and low toxicity, they pose no threat to groundwater.
Breakdown of Chemical in Water
The EPA has not issued restrictions for the use of B.t. around bodies
of water. It can be effective for up to 48 hours in water. Afterwards, it
gradually settles out or adheres to suspended organic matter (2).
Breakdown of Chemical in Vegetation
Since it does not spread, B.t. must be applied to the parts of the
plants that are normally attacked by lepidopterous larvae, or to the
particular zones of water in which dipterous larvae feed. It is relatively
short-lived on foliage because the ultraviolet (UV) light of the sun
destroys it very rapidly, and rain washes it onto the soil. The bacterium
is nonphytotoxic, or not poisonous to plants, and has not shown any adverse
effect upon seed generation or plant vigor (2).
PHYSICAL PROPERTIES AND GUIDELINES
The insecticidal action of B.t. is attributed to protein crystals
produced by the bacterium. The vegetative cells of B.t. are approximately
one micrometer (mcm) in width and 5 mcm in length, and are motile (12).
The commercial product contains about 2.5 x 10 to the 11th viable spores
per gram. Typical agricultural formulations that contain spores and
protein crystals include wettable powders, spray concentrates, liquid
concentrates, dusts, baits, and time release rings (4, 6, 14).
B.t. products should be stored in a cool, dry place. Some loss of
effectiveness can be expected in products stored for more than six months
(2). Formulated products are compatible with most insecticides,
acaricides, fungicides and plant growth regulators; they are not compatible
with captafol, dinocap, alkaline sprays or, under some conditions, leaf or
foliar nutrients (4, 14).
Physical Properties
| CAS #: | (B.t. variety kurstaki) 68038-71-1 |
| H2O solubility: | emulsifies (3); suspendable (10); -- vars. israelensis and kurstaki: insoluble in water (4) |
| Solubility in other solvents: | vars. israelensis and kurstaki: insoluble in organic solvents (4) |
| Flash point: | over 400 degrees, var. kurstaki (3) |
| Chemical Class/Use: | Biological insecticide |
| There have been reports of air emissions of 0.5 kg of particulates per
metric ton of pesticide produced (11) |
BASIC MANUFACTURERS
Sandoz Crop Protection Corp.
1300 E. Touhy Ave.
Des Plaines IL 60018
Abbott Laboratories
Chem. and Agric. Prod. Div.
1401 Sheridan Rd.
North Chicago, IL 60064
Review by Basic Manufacturer - Abbott Labs:
Comments solicited: November, 1992
Comments received:
Review by Basic Manufacturer - Sandoz:
Comments solicited: November, 1992
Comments received: December, 1993
REFERENCES
Abbott Laboratories. 1982 (Oct.). Toxicology profile: Dipel,
Bacillus thuringiensis insecticide. Chemical and Agricultural Products
Division. North Chicago, IL.
Agriculture Canada. 1982. Report of new registration: Bacillus
thuringiensis Serotype H14. Food Protection and Inspection Branch.
Ottawa, Canada: Agriculture Canada.
Agway, Inc. No date given. Material safety data sheets (on Bacillus
thuringiensis formulations). Chemical Division. Syracuse, NY.
Berg, G. L. (ed.). 1986. Farm chemicals handbook. Willoughby, OH:
Meister Publishing Company.
Harper, J. D. 1974 (Dec.). Forest insect control with Bacillus
thuringiensis. Survey of current knowledge. Agricultural Experimental
Station. Auburn University. Auburn, AL: University Printing Services.
Hayes, W. J. 1982. Pesticides studied in man. Baltimore, MD:
Williams and Wilkins.
International Minerals and Chemical Corporation. (No date given)
Thuricide technical bulletin. Bioferm Division, Microbial Insecticide
Department. Wasco, CA.
McEwen, F. L. and G. R. Stephenson. 1979. The use and significance
of pesticides in the environment. NY: John Wiley and Sons, Inc.
National Coalition Against the Misuse of Pesticides. 1986 (Dec.)
Pesticides and you. Washington, DC.
Nor-Am Chemical Company. 1985. Material safety data sheet:
Bacillus thuringiensis. Wilmington, DE.
Sittig, M. 1980. Pesticide manufacturing and toxic materials
control encyclopedia. Parkridge, NJ: Noyes Data Corporation.
U.S. Environmental Protection Agency. 1986. Pesticide fact sheet
for Bacillus thuringiensis. Fact sheet no. 93. Office of Pesticide
Programs. Washington, DC.
Ware, G. W. 1982. Fundamentals of pesticides. A self-instruction
guide. Fresno, CA: Thomas Publications.
Worthing, C. R. (ed.). 1983. The pesticide manual: A world
compendium. Croydon, England: The British Crop Protection Council.
Meister, R.T. (ed.). 1992. Farm Chemicals Handbook '92. Meister
Publishing Company, Willoughby, OH.
Spiegel, J.P. and J.A. Shadduck. 1990. Clearance of Bacillus
sphaericus and Bacillus thuringiensis ssp. israelensis from mammals. J. of
Economic Entomology 83 (2): 347-355.
Vandenberg, J.D. 1990. Safety of four entomopathogens for caged
adult honeybees (Hymenoptera: Apidae). J. of Economic Entomology 83 (3):
756-759.
Dunkle, R.L. and B.S. Shasha. 1989. Response of starch-encapsulated
Bacillus thuringiensis containing ultraviolet screens to sunlight.
Environmental Entomology 18 (6): 1035-41.
Roe, R.M. et. al. 1991. Vertebrate toxicology of the solubilized
parasporal crystalline proteins of Bacillus thuringiensis susp.
israelensis in Hodgson, E., R.M. Roe and N. Motoyama (eds.). Reviews in
Pesticide Toxicology 1: Pesticides and the Future: Toxicological Studies of
Risks and Benefits. North Carolina State Univ., Raleigh, NC.
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are for convenience only; no endorsement of products is intended, nor is
criticism of unnamed products implied. Most of this information is historical
in nature and may no longer be applicable.
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