One of Natures Insecticides

Bt, or Bacillus thuringeiensis, is a useful addition in the arsenal
against plant-eating insects. Bt is a naturally occurring bacteria
that is common all across the world, and early in the twentieth
century it was discovered to be an excellent form of insect control.

Bt became available to home gardeners in the 1950s but in recent
years new strains have been developed that attack an even wider
range of insects.

The kurstaki strain of Bt kills only caterpillars that feed on
leaves and needles. Bt kurstaki is especially useful for eliminating
corn earworms and those little green cabbage worms, that like to
infest broccoli, along with tent caterpillars and webworms that
damage trees and shrubs. Because Bt kurstaki will kill most any
type of caterpillar, it should be used carefully and sparingly if you have a
butterfly garden or seek to attract more butterflies to your garden.

Another type of Bt, the israelensis strain, will kill the larvae
of mosquitoes, black flies and fungus gnats. This is good news
for those of you who suffer through black fly season each summer!

The san diego strain of Bt is a good choice for controlling the
Coloradopotato beetle. Potato beetles can quickly reduce potato
plants to shreds, but Bt san diego stops the larvae in their tracks
before they can do significant damage.

Each strain of Bt is specific to certain pests. Bt israelensis and
san diego will not harm caterpillars, and likewise, Bt kurstaki will
not harm black flies or potato beetles. Bt acts by producing
proteins that react in the gut of the insect, paralyzing their
digestive system. The insects stop eating and quickly starve.

Bt is not harmful to plants, people or pets, although you should
avoid breathing the powder or spray when applying Bt to your plants.
Bt also degrades fairly quickly in sunlight, so it will not persist
in your garden. Some strains persist for less than 24 hours while
others remain viable for about a week.