10 Neat About Bt
by Dorothy Dobbie
by Dorothy Dobbie

The Local Gardener magazines, Ontario Gardener, Manitoba Gardener and Alberta Gardener, are published by Pegasus Publications Inc.

Drawing on her 30 years' experience as a senior executive in the magazine publishing industry, Dorothy launched Manitoba Gardener in 1998, initially running the business out of her home. Two years later, Dorothy's daughter Shauna, living in Ontario, jumped into the fray with Ontario Gardener. And two years after that, they started Alberta Gardener. Visit us at and register for our "Ten Neat things" newsletter. Watch Shaw TV for garden tips and Listen to CJOB for the Gardener Sundays at 9:08

October 15, 2017

1. A better bug.

Bacillus thuringiensis is the tiniest kind of bug - it's one of those soil-borne bacteria that has a key place in the natural order of things. It can be found in the gut of all kinds of caterpillars, moths and butterflies. It has no impact on animals of the two- or four-legged kind, but certain strains are very unfriendly toward said caterpillars and moths, as well as toward flies, mosquitoes, sawflies, beetles and some nematodes.

2. Bt is not new news.

We've known about this particular bug since it was discovered in 1901 by a Japanese biologist, who found it in a dead silkworm. Everybody ignored him though, until 1911, when the bacterium was "rediscovered" by a German scientist, this time in a flour-moth larvae.

3. In your face and on your back.

Bt is the most widely used insecticide in the world and it's right in your face, as in your mouth, when you ingest corn bio-engineered to resist insect infestation, and on your back in the cotton shirts you wear. About 40 per cent of U.S.-grown corn contains Bt and about half the cotton.

4. Mosquito infanticide.

This bacterium has many specialist strains that target only certain species. One such is Bacillus thuringiensis israelensis (Bti) which attacks the larvae of pesky animals such as mosquitoes, fungus gnats and blackflies.A product that is used to stop mosquitoes from reproducing in ponds and bird feeders is called "Mosquito Dunk".

5. Killing the caterpillar kind.

The strain, Bacillus thuringiensis kurstaki, is effective against the larvae (caterpillars) of lepidopterans, such as forest tent caterpillars, gypsy moths and spruce budworms. Sprayed on trees, the leaves retain the bacteria for a week or so, and rain can wash it back into the soil. When the caterpillars eat the leaves, a crystal in the bacteria is activated in the gut of the insect and slowly destroys its digestive system.

6. Potato beetle.

A subspecies, Bacillus thuringiensis kurstaki var. tenebrionis, is effective against the larvae of the Colorado potato beetle when the larvae are still in their first two instars, but it has a tougher time with later instars and larger larvae.

7. Higher-ups from Health Canada.

As for environmental risk, Health Canada anticipates none, but there is a danger that the insects could become resistant to the bacteria. However, given the habits of bacteria as we know them, they will no doubt be able to overcome this - the types that attack humans certainly can.

8. Sunlight kills.

Using Bt against insects means several applications and a bit of patience as exposure to sunlight will reduce the life span of the bacteria.

9. NewLeaf but bad news.

When, in 1995, Monsanto introduced a potato variety containing Bt toxin-producing genes to combat the Colorado potato beetle, the hue and cry from environmentalists was fierce. The potato was withdrawn.

10. Bt good news or bad news?

Debate continues to rage about genetically engineered crops, but one effective argument is that Bt-modified crops reduce chemical pesticide use. Bt has been used as an insect control for almost 100 years with no discernible ill effects.

Dorothy Dobbie Copyright© Pegasus Publications Inc.

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