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.
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
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
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
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.
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, 18.104.22.168 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.