Bacillus thuringiensis is a miraculous biological weapon against mosquitoes, boxwood borers, and potato beetles. Let us enlighten you on how to use this bacterium to combat garden pests.
Bacillus thuringiensis is a much-helpful bacteria in organic farming as well as among home gardeners, as it is a key element in many eco-friendly insecticide formulations. Bacteria have a bad reputation due to their common name, but bacillus is a good bacteria and therefore we’ll clear things up for you in this post.
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What exactly is Bacillus thuringiensis?
Bacillus thuringiensis (Bt) is an air-breathing soil bacterium that is widely spread, i.e. found all over the world. A Japanese scientist named Bacillus sotto named it after the bacterium he found inside a silkworm in 1901. A similar bacterium was discovered in a damaged flour moth caterpillar in 1911 by a German scientist.
Bacillus thuringiensis was the term given to the bacteria because it was discovered in a mill in Thuringia. This name has lasted to this day. Since then, scientists have discovered and studied numerous subspecies and strains around the world. Insect larvae are a valuable food source for some subspecies, as they are parasitized and killed by them.
Biological Pest Control using Bacillus thuringiensis
Here are some of the important aspects to understand before using Bio Bt based pest control methods.
How does Bacillus thuringiensis work?
A feeding insect’s larva ingests the bacterium by swallowing it. For the purpose of reproduction, this bacterium creates spores in the larva’s intestine. Crystalline toxins, on the other hand, are created, but they have no effect when they are formed.
Toxins are dissolved in the insect larva’s intestine if the pH is appropriate. Digestive enzymes in the larva then cleave them, making them active. The poison is now bound to the intestinal wall of the larva via appropriate receptors. The gut wall is breached and destroyed as a result.
Toxic metabolic poisons in the body cavity of germinating bacterial spores kill both the larva and its intestinal tract at the same time. Bacillus thuringiensis can therefore easily be envisioned as a component of insecticides and biocides.
Note on Bt corn and Bt soy: A change in the plant’s genes is what’s behind the “Bt” moniker. These corn and soybean types have a bacterial gene inserted, which the plant uses to generate and store the crystalline toxin. A pest caterpillar that feeds on the Bt plants will be killed by that toxin. It is completely safe for humans and other untargeted organisms to consume Bt corn or Bt soy.
Bacillus thuringiensis Preparations Based on the Pests
Four subspecies of Bacillus thuringiensis have been approved for use in crop protection products in many of the western nations.
| Bacterium Subspecies | Affected Pests |
| B.t. kurstaki | Certain butterflies (order Lepidoptera, excluding Noctuidae) |
| B.t. aizawai | Certain butterflies (orders Lepidoptera, including Noctuidae) |
| B.t. israelensis | Two-winged moths, including mosquitoes and midges |
| B.t. tenebionis | Garden leaf beetles, e.g. potato beetles |
Advantages of Bt preparations
It is common in organic farming to employ crop protection products that contain Bacillus thuringiensis as the active ingredient. The use of several preparations in hobby gardens has been permitted as well. The following are some of the benefits of Bt preparations:
- They may be employed on a regular basis (unlike synthetic pesticides).
- These products provide almost no danger to the end user, since just a few sporadic occurrences of allergic reaction to the skin or eyes have been reported.
- Even with frequent application, there is little or no resistance on the part of the target species.
- Organisms that aren’t part of the target pest population are completely unaffected.
#Note: UV radiation as well as rainfall reduce the effectiveness of Bt compounds over time, necessitating more frequent application. Reapplication is also necessary when a new pest generation emerges.
How to Apply or Use Bacillus thuringiensis for Controlling Pests
There are dry powders on the market that contain the inactive survival forms of Bacillus thuringiensis. The bacteria come back to life when reconstituted with water. In order to combat mosquitoes, B.t. israelensis is sprayed directly into rain barrels or fish ponds, and then applied with a conventional garden sprayer.
Refer to the product’s package insert in each case for specific instructions on how to use the product in an effective, safe, and environmentally sound manner. Please be aware that Bt preparations are only effective at temperatures greater than 15°C.
Insect infestations, such as those caused by beetles and mosquitoes, can be avoided only then. These insects, as well as butterfly and mosquito larval stages are required for the bacterium to be sufficiently active and absorbable by feeding.
Keep in mind that Bt preparations have a shelf life of two to three years while storing them. Because opened packets expire after a few months, opting for items in sachets saves you money in the long run.
Bacillus thuringiensis against the Boxwood Borer
This bacterium (specifically the Bacillus thuringiensis aizawai strain) is powerful against free-feeding butterfly caterpillars such as the boxwood borer (Cydalima perspectalis), winter moth (Operophtera brumata), cabbage white butterfly (Pieris brassicae and Pieris rapae), and oak processionary moth (Thaumetopoea processionea) and the Garden pebble moth (Evergestis forficalis). The boxwood borer can be controlled organically, without the use of chemical pesticides, therefore avoiding damage to other insects in our environment from non-specific pesticides.
Bacillus thuringiensis: Effects on other Organisms
Humans have developed highly specialised subspecies of the Bt bacterium, which is why they can be employed to combat pest problems without having any negative impacts on other organisms. There are specific digestion enzymes and receptors that are activated only when an infective insect larva consumes the bacterium.
Toxins from Bacillus thuringiensis have little or no effect on other creatures that consume it. As a result, bees and other pollinating insects are unaffected. Bt preparations must be treated with the same care as any other crop protection product, regardless of the specifics.
Can Bacillus thuringiensis harm humans?
Humans and pests (insect larvae) are two biologically and genetically different species. Bacillus thuringiensis has been developed to ONLY target the intended pests. Extensive studies have been conducted in the past to see if it has any negative impacts on humans, animals or other organisms. Bacillus thuringiensis was shown to have no effect on the great majority of people who were exposed to it in large doses.