About the Btk Spray

Btk (Bacillus thuringiensis var. kurstaki) is an
organic insecticide that contains a naturally-occurring bacterium
found in soil.

Btk, when applied at recommended rates, does not harm people,
plants, animals or any insects - except for caterpillars. This is
because the bacteria only become active in the caterpillar’s
uniquely alkaline gut.

Btk is mist sprayed in small amounts - only 5 litres of product per
hectare (an area slightly bigger than a rugby field).

The spray has a long history of safe use. Btk has been used in many
countries to protect agricultural crops, fruit trees and forests for
more than 30 years. New Zealand organic growers have been using Btk
spray since 1984.

It has been successfully used for control and eradication of gypsy
moth in a number of cities and towns in North America with no or just
a few adverse effects on urban populations.

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Btk Facts

What is Btk?

Bacillus thuringiensis var. kurstaki (Btk) is a
bacterium that occurs naturally in soil, foliage, water and air in
most countries in the world, including New Zealand. Btk is used to
control moth and butterfly pests around the world.

Commercial formulations of Btk are produced by a number of American
and European companies. Large quantities have been used over the past
30 years in North America, particularly to control gypsy moth and
tussock moth populations.

Btk has been chosen as a preferred spray for aerial application
against painted apple moth because it specifically targets
caterpillars, does not grow in warm-blooded organisms (animals or
humans), is not infectious, is readily available commercially and is
one of the safest insecticides known.

In 1996-97 Btk was used successfully during Operation Evergreen to
eradicate white-spotted tussock moth from the eastern suburbs of
Auckland. An independent health study was done to assess the health
risks of the spray. It found no evidence of adverse health concerns,
although there were instances of minor respiratory irritations at the
time of spraying.

An independent health monitoring programme will be undertaken in
conjunction with painted apple moth spraying in west Auckland.

What else is in the spray?

The spray contains mostly water, traces of essential elements,
minerals or salts, and "inert" ingredients such as
thickening, sticking and wetting agents. All the ingredients (as
assessed by New Zealand medical experts) are of extremely low
toxicity.

Every batch is thoroughly tested - during the years that it has
been produced, no batch has caused any negative effect or been
rejected.

How does Btk work?

Btk is sprayed on to foliage. The foliage must be eaten by
caterpillars before it can take effect. Once it has been eaten, the
toxin in Btk is activated by the alkaline gut contents of the
caterpillar, causing gut paralysis. Minutes after eating, the
caterpillar will stop feeding, and will die about two to three days
later (depending on conditions such as the age and size of the
caterpillar, and air temperature).

How is Btk different from other insecticides?

Btk is a biological insecticide and not a chemical. It acts
specifically on caterpillars and does not harm other insects, animals
or plants. It breaks down relatively quickly in the environment
through exposure to UV light and other microorganisms.

Where else has it been used against caterpillars?

Btk is used world-wide to protect vegetable and horticultural crops
and forests. More than 500, 000 kilograms of Btk are applied annually
in the United States alone. Foray 48B ( one particular Btk
formulation) has been widely used in Canada against gypsy moth. This
has included programmes in large urban areas - for example, 19, 000
hectares in Vancouver in 1992.

Many countries, including New Zealand, routinely use Btk as an
agricultural spray. However, these may be different formulations from
Foray 48B. The main brands used in New Zealand are Dipel, Delfin and
Agree - these are registered for use on horticultural crops.

Does Btk affect people or animals?

The Pesticides Board has approved foray 48B for aerial spraying in
New Zealand. The Ministry of Health also assessed the product to
ensure its safety in 1996/97 when Operation Ever Green took place to
eradicate the white-spotted tussock moth.

Btk has been used in commercial pest management for over 30 years
in Canada and the United States. Extensive studies have been carried
out during that time, as required by the United States Environmental
Protection Agency and Health and Welfare Canada and no significant
adverse effects on animal or human health were recorded.

People - in New Zealand in 1996, Auckland Healthcare
Services (A+) commissioned a study into the health risks of spraying
with Btk during Operation EverGreen. The study found Btk is not a
recognised cause of human infections and is highly unlikely to cause
illness through contamination of food. While the spray also contains
food residues, preservatives, an acidity regulator, an alcohol and a
sugar-like substance as a stabiliser, these ingredients are approved
food additives.

However, people who had concerns could reduce exposure to the spray
by leaving the area during the spray operation. A further health risk
assessment is being carried out prior to any aerial spraying to
eradicate painted apple moth.

The most likely ways for people to be exposed to Btk as a direct
result of aerial spraying are through direct contact with the
formulation on skin or eyes (for workers using the spray), or direct
contact with the spray on the skin, in the mouth or eyes, or through
inhalation.

All North American studies to date show no public health concerns,
despite long-term, large-scale use of Btk in aerial pest management
programmes. This is because Btk is activated only by specific
conditions that exist in the gut of the caterpillar. The studies found
no evidence of any poisonous, infectious or disease-causing
effects.

In extremely rare cases people spraying Btk may develop minor,
transient irritations such as dry skin, chapped lips, itchy, red and
burning eyes, runny noses and nasal stuffiness. However, spray workers
studied in Vancouver who reported such problems had been exposed to up
to 500 times more Btk than a member of the public outdoors during the
spray operation.

Animals - Btk is specific to the caterpillars of moths and
butterflies, so it is likely to kill all exposed young caterpillars.
However, native caterpillar populations are expected to quickly
recolonise the sprayed zone from the surrounding areas. Adult moths
and butterflies are not affected.

Btk is not toxic to bees and does not affect spiders, beetles,
snails, shellfish and worms or most other insects and
invertebrates.

Animals may be exposed through eating plants or insects sprayed
with Btk, inhaling or absorbing Btk through the skin. However, Btk is
only activated by specific conditions in caterpillar’s alkaline
guts and does not grow in warm-blooded animals.

The only potential effect on birds is a temporary decrease in food
supply in those that rely heavily on caterpillars for food. These
species may have to spend more time foraging for food.

The greatest impact of the Btk spray programme on animals in New
Zealand appeared to be through the effects of noise from low flying
aircraft on domesticated animals.

Fish - field studies and ongoing monitoring of
fish populations have found no effects on fish behaviour, feeding
patterns or reproduction resulting from spray programmes in Canada and
the US in the last 20 years.

Does Btk affect soil, water, plants or food?

Soil - Btk occurs naturally in soils throughout the world,
including New Zealand. Tests have shown that it does not change the
soils’ productivity or fertility.

Water - Btk may enter water through direct application,
run-off or through the faeces from animals that have eaten it. Tests
have shown it may persist for several months in fresh water (and for a
much shorter time in seawater). However, it does not leach out of the
soil into groundwater and does not affect aquatic organisms.

Plants - if anything, Btk should help plants by reducing the
populations of leaf-feeding caterpillars. It has no direct toxic
effects on New Zealand plants.

Food - Btk is often used by the food industry (on kiwifruit,
citrus trees, grape vines and berry fruit) to control pest
caterpillars. It is also widely used on organic crops, with no holding
period required before sale or consumption. As Btk does not grow in
warm-blooded organisms, it passes through the digestive system without
producing any toxic effect.

What precautions are being taken to ensure no mistakes are
made?

The Ministry of Agriculture and Forestry, which is the agency
managing the Government’s response to painted apple moth, will
ensure:

• people working with Btk follow the manufacturer’s
  instructions regarding safe use;
• all workers are fully trained;
• all equipment is properly maintained and calibrated;
• all workers are supplied with, and wear, appropriate protective
  equipment;
• the spray application is at the right level to kill the insects,
  precisely timed, done with well maintained equipment and trained
  people, and only during favourable weather conditions;
• areas are targeted specifically by spraying only when
  meteorological conditions were favourable, and using the right
  equipment;
• noise effects are minimised with standard flying
  precautions;
• any remaining Btk is disposed of according to the
  manufacturer’s instructions;
• a public information programme will inform people about the
  precautions they could take if they were concerned about possible
  exposure;
• appropriate liaison with the Department of Conservation,
  scientific community and local environmental groups to identify and
  protect any biologically sensitive areas;
• the programme is continually monitored.

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Further Reading

Recently published book by well known New Zealand scientists, Dr
Travis Glare and Dr Maureen O’Callaghan, Bacillus
thuringiensis: Biology, Ecology and Safety , published by John
Wiley & Sons in 2000, provides an objective and scientifically
credible reading on the subject of Btk.

This summary of Btk was drawn from a variety of sources. For those
who want more information, there are additional references listed
below. Please note that some are not readily available in published
form.

Agriculture Canada, CRD Health, c1992. Health Concerns
Associated with Aerial Spraying of Btk for Gypsy Moth Control. In
Information Submitted to BC Environmental Appeal Board March 1993 by
Agriculture Canada. pp 441-442.

Agriculture Canada, 1993. Information Submitted to BC
Environmental Appeal Board. 603p.

Anonymous, 1980. Operational field trials against the
Douglas-fir tussock moth with chemical and biological insecticides. An
international research and control programme conducted in British
Columbia, 1975-1976. SO: Information-Report, Canadian Forestry
Service. 1980 No BC-X-201, 19p.

BC MOH, 1992 (Ministry of Health, Vancouver, British
Columbia, Canada). Bacillus thuringiensis. In Information Submitted to
BC Environmental Appeal Board by Agriculture Canada 1993. pp
443-454.

California Department of Food and Agriculture, 1992. Final
Environmental Impact Report; Gypsy moth, Lymantria dispar (L.),
Eradication Program in California. State Clearinghouse Number
90021090.

Cowley, JM; Bain, J; Walsh, PJ; Harte, DS; Baker, RT; Hill, CF;
Whyte, CF; Barber, CJ, 1993. Pest Risk Assessment for Asian Gypsy
moth, Lymantria dispar L. (Lepidoptera: Lymantriidae). Lynfield Plant
Protection Centre, MAF, Auckland, New Zealand.

Ellis, Roy, 1991. BTK. In Information Submitted to the BC
Environmental Appeal Board March 1993 by Agriculture Canada. pp
193-236.

Faulds, W, 1994. Indigenous Lepidoptera Susceptible to
Control Measures Taken Against Asian Gypsy Moth. (Unpublished). New
Zealand Forest Research Institute, Rotorua, New Zealand.

Hayes, WJ; Laws, RE, 1991. Handbook of Pesticide Toxicology,
Volume 2, Classes of Pesticides, 13.12.1.2 Bacillus thuringiensis -
Toxicity to Laboratory Animals. Academic Press, Inc. Harcourt Bruce
Jovanovich, Publishers.

Lehnert, Thor; Cantwell, George, 1978. The effects of
microbial pesticides on the honeybee - a review. American Bee Journal
vol 118 (10) p 674-675. In Information Submitted to BC Environmental
Appeal Board March 1993 by Agriculture Canada. pp 164-165

Mastro, V, 1994. Proceedings Gypsy Moth Review 30 October -
2 November, Portland US, Unpublished. Update on Mating Disruption as a
Control Strategy. USDA, APHIS, PPQ, Otis MDC, Massachusetts, US.

Menon, AS; De Mestral, J, 1984. Survival of Bacillus
thuringiensis var. kurstaki in waters. In Information Submitted to BC
Environmental Appeal Board March 1993 by Agriculture Canada. pp
91-97.

Miller, Jeffrey C, 1990. Field Assessment of the Effects of
a Microbial Pest Control Agent on Non-target Lepidoptera. American
Entomologist. Summer 1990. In Information Submitted to BC
Environmental Appeal Board March 1993 by Agriculture Canada. pp
116-120.

Ministry for the Environment, 1987. Environmental Protection
and Enhancement Procedures 1987 Revision. MFE, Wellington.

Nowak, Ronald, 1995. Walkers Bats of the World. John Hopkins
University Press, London.

Noble, MA; Riben, PD; Cook, GJ, 1992. Microbiological and
Epidemiological Survey Programme to Monitor the Health Effects of
Foray 48B Btk Spray. Departments of Pathology and Health Care and
Epidemiology, University of BC, and University Hospital, Vancouver, BC
Canada.

Novo Nordisk, no date. Foray 48B Inert Ingredients In
Information Submitted to BC Environmental Appeal Board March 1993 by
Agriculture Canada. pp 390-392.

Ontario Ministry for the Environment Water Resources Branch,
Aquatic Criteria Development Committee, June 1989. Review of Btk
for use in forest pest management programmes in Ontario with special
emphasis on the aquatic environment. In Information Submitted to BC
Environmental Appeal Board March 1993 by Agriculture Canada. pp
121-139.

Perrin, CJ; Richardson, JS, 1993. Effects of the bacterial
insecticide Bacillus thuringiensis var. kurstaki (Btk) on an aquatic
insect community. Report prepared by Limnotek Research and Development
Inc. Vancouver BC for BC Ministry of Forestry, Silviculture Branch,
Victoria. In Information Submitted to BC Environmental Appeal Board
March 1993 by Agriculture Canada. pp 98-100.

Rossiter, Marycarol; Yendol, William; Dubois, Normand R,
1990. Resistance to Bacillus thuringiensis in Gypsy Moth
(Lepidoptera: Lymantriidae). Genetic and Environmental Causes. Journal
of Economic Entomology Vol 83 No 6.

Samples, JR; Buettner, H, 1983. Ocular Infection Caused by a
Biological Insecticide. The Journal of Infectious Diseases; Vol. 148
No. 3. The University of Chicago.

Sato, T, 1977. Life history and diapause of the
White-spotted tussock moth Orgyia thyellina Butler (Lepidoptera:
Lymantriidae). Japanese Journal of Applied Entomology 21(1): 6-14.

Schaffer, Cindy, 1992. Memorandum on SACB review of adverse
effects data to Foray 48B, a Bacillus thuringiensis based microbial
pest control agent. US EPA Office of Pesticides and Toxic
Substances.

USDA, 1995 (United States Department of Agriculture, Forest
Service, Animal and Plant Health Inspection Service). Gypsy Moth
Management in the United States: a Co-operative Approach. Final
Environmental Impact Statement (5 vols).

Watts, R, 1992. Conduct of Fish Toxicity Tests on Foray 48B
(Unpublished Laboratory Report). Conservation and Protection, Aquatic
Toxicity Laboratory, Vancouver, BC, Canada. In Information Submitted
to BC Environmental Appeal Board March 1993 by Agriculture Canada.

Weber, Wayne C, 1993. Potential effects of gypsy moth
spraying on songbirds in south coastal British Columbia. BC Ministry
of Agriculture, Fisheries and Food. In Information Submitted to BC
Environmental Appeal Board March 1993 by Agriculture Canada. pp
238-246.

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