Environmentally Safe, Effective Worm Control
We should be cautious when using pesticides because, obviously, they are
poisonous. If they weren't poisonous, pesticides wouldn't kill pests. There
is, however, an alternative to pesticide use.
Insect larvae, or worms and caterpillars, can cause considerable damage
to gardens. Good news! There is a pesticide which kills worms but is not
poisonous to man or beast. The worm-killer is the bacteria Bacillus thuringiensis,
or BT for short.
When ingested, BT produces a toxic substance within the cells of its victims.
Only certain species of caterpillars are affected by BT. The infection occurs
only when the caterpillars feed on plant foliage which is being protected
by BT. Adult insects which feed mainly on plant nectar are not affected.
Only the destructive caterpillars are killed; the good bugs are spared.
BT is not a merciful killer. Death is slow and painful. The first symptom
experienced by a BT victim is "gut" paralysis. This means an immediate
cessation of foliage ingestion. But BT doesn't stop there. Eventually, it
causes a breakdown in the gut wall and leakage of contamination into the
body cavity of the larvae. Since the body cavity tissues of a caterpillar
are bathed by blood in an open circulatory system, the larval blood offers
an ideal growing condition for growth of this contamination.
BT contamination produces spores which rapidly divide. In fact, a new generation
of spores is produced every 20 minutes. Therefore, after just 12 hours,
one spore can produce 6,719,476,736 new BT's. Obviously, this quantity needing
nourishment from caterpillars has a devastating effect.
BT is terminal. All infected larvae become sick and most die. This is because
insects do not have an effective immune system as humans and other mammals
do. In theory, lack of an effective immune system dictates that susceptible
species will not develop a resistance to BT.
Outward symptoms of caterpillars infected by BT are manifested as behavior,
color and morphological changes. As soon as they are infected, larvae quit
feeding. They usually move from their normal feeding sites to exposed leaf
surfaces. Before dying, they become sluggish, discolored and usually exhibit
regurgitation and diarrhea. Cadavers of large larvae become limp, but do
not "liquefy" as viral-infected larvae do. Cadavers of small larvae
are often difficult to find because they turn black and shriveled.
Usually, one taste of BT is enough to destroy susceptible larvae. However,
in some instances a larva may not die from BT, but suffer a fate worse than
death. These symptoms include:
- A predisposition to other naturally occurring pathogens, such as
other bacteria, fungi and viruses.
- Starvation due to digestive track disruption.
- Failure to pupate due to physiological malfunctions.
- An increased susceptibility to predators and parasites as a result
of sluggish movement and migration to exposed leaf surfaces.
- Increased sensitivity to harsh climatic factors, such as high or
low temperatures.
- Reduced reproductive potential. Infected larvae that do successfully
mature are abnormally small and weak adults. They are significantly less
fertile than normal adults and incapable of successful mating.
Anything which causes as many horrible symptoms as BT does should certainly
be respected. The alkaline pH gut (pH greater than 7.0) of susceptible caterpillars
activates BT. Acid-gutted or stomached creatures cannot be affected; thus,
humans and mammals are not in any way affected by BT. Only susceptible caterpillars
have the necessary combination of pH, salts and enzymes in their digestive
system to activate BT.
BT was discovered in 1915 by a German named Berliner. He isolated this unique
pathogen and named it Bacillus thuringiensis after the town of Thuringia,
Germany. BT is a naturally-occurring bacterium that causes a deadly disease
specific to certain Lepidopterous (caterpillar) insects.
BT products do not have any of the hazards sometimes associated with chemical
insecticides. BT is biodegradable in the environment, and rapidly deactivated
in soil with a pH below 5.1. Rainfall, exposure to sunlight and, in some
cases, the type of foliage on which it is sprayed may cause BT spores and
crystals to lose their viability over time. The bacteria may remain effective
for as long as 22 days, or may become ineffective after 24 hours, depending
on conditions. Under normal conditions, BT products are active for three
to seven days after spraying. In comprehensive spray programs on some crops,
repeated application is recommended at regular intervals.
BT is available in local nurseries under the names of Thuricide, Dipel,
Bactus, Biological Worm Control, Leptox, SOK, Novabac or Tribacture. Since
BT is such an effective plant-damage deterrent, it should be spread around
- especially on the surface of leaves. This can be accomplished by adding
a teaspoon of liquid soap per gallon of spray. The soap breaks the surface
tension on the leaf's surface and allows the BT product to spread evenly.
This allows more leaf area to be protected by BT.
With BT, you can rid plants of those devastating worms without endangering
yourself or the environment, a truly EARTH-KIND practice.¶