Bacillus thuringiensis as a miracle weapon against mosquitoes, box tree moths and potato beetles - and that organically? We'll enlighten you.
The bacterium Bacillus thuringiensis is popular both in organic farming and among hobby gardeners because it forms the active ingredient in very environmentally friendly insecticides. Because his name doesn't inspire much confidence and you'd rather stay away from germs, we'll provide you with comprehensive information in this article.
Bacillus thuringiensis
We explain exactly what Bacillus thuringiensis is, how it works and which preparations contain it. Then we go into the use against the box tree moth, which is important for many hobby gardeners, and clarify whether the bacterium can also damage other organisms or even humans.
What exactly is Bacillus thuringiensis?
The bacterium with the name Bacillus thuringiensis (Bt) is an air-breathing soil bacterium that is ubiquitous, i.e. omnipresent worldwide. When it was discovered inside a silkworm by a Japanese scientist in 1901, he named it Bacillus sotto. In 1911, a German scientist also isolated such a bacterium from a diseased flour moth caterpillar. Because this caterpillar came from a mill in Thuringia, he named his discovery Bacillus thuringiensis - a name that has endured to this day. Since then, various subspecies and strains have been described and researched around the world. Some subspecies possess a property that is very useful to humans: they parasitize and kill insect larvae.
How does Bacillus thuringiensis work?
- The bacterium is ingested by a feeding insect larva through the mouth.
- It forms spores in the intestines of the larva in order to reproduce. At the same time, crystalline toxins are formed which have no effect in their initial form.
- If there is a suitable pH value in the intestine of the insect larva, the toxins are dissolved. They are then split by the larvae's digestive enzymes and thus activated.
- The toxin now binds to appropriate receptors on the intestinal wall of theLarva. This will be opened and destroyed.
- The larva dies at the same time from the destruction of its intestinal tract and from blood poisoning, which is caused by metabolic toxins from the germinating bacterial spores in the body cavity.
So it's easy to imagine that Bacillus thuringiensis can be used in insecticides and biocides.
Note on Bt maize and Bt soya: Behind the designation as Bt maize or Bt soya there is a modification of the plant genes. A bacterial gene was added to these corn and soybean varieties, with the help of which the plant itself produces the crystalline toxin and stores it in its leaves. If a suitable caterpillar eats on the Bt plants, it will be killed.
Bacillus thuringiensis preparations
Four subspecies of Bacillus thuringiensis have so far been approved in plant protection products in Germany.
| Bacteria Subspecies | Affected insects |
|---|---|
| B.t. kurstaki (B.t.k.) | Specific Lepidoptera (Order Lepidoptera, excluding Noctuidae) |
| B.t. aizawai (B.t.a.) | Certain butterflies (orders Lepidoptera, also Noctuidae) |
| B.t. israelensis (B.t.i.) | Birds, including midges and mosquitoes |
| B.t. tenebionis (B.t.t.) | Leaf beetle, e.g. potato beetle |
Bt Supplement Benefits
Pesticides that use Bacillus thuringiensis as an active ingredient are particularly popular in organic farming and can be used in many ways there. Some preparations are also approved for use in the hobby garden, such as our Plantura Zünslerfrei XenTari®. The benefits of Bt supplements are as follows:
- They may (unlike synthetic pesticides) be used frequently
- They hardly pose any danger for the user - allergic reactions of the skin and/or eyes only occur in isolated cases
- On the side of the target organisms, hardly any resistances are observed even with frequent use
- Non-target organisms are unaffected or only marginally affected
Note: Bt products tend to need to be applied more often as UV exposure and precipitation reduce their effectiveness over time. Even if a new generation of pestsgrowing, reapplication is necessary.
Application of Bacillus thuringiensis
Bacillus thuringiensis is sold as a dry powder containing inactive perennial forms. When mixed with water, the bacteria come back to life. They can then be applied with a conventional sprayer or - in the case of B.t. israelensis against mosquitoes - poured into rain barrels or ponds. The effective, safe and environmentally friendly application and dosage can be found in the package insert of the product in each individual case. It is important that Bt preparations are only effective at temperatures above 15 °C. Only then are beetle, butterfly and mosquito larvae sufficiently active and ingest the bacterium in sufficient quantities through food. When it comes to storage, it is important to note that Bt preparations only have a shelf life of two to three years. Opened packs can only be used for a few months, so it is worth buying products with sachets.
Bacillus thuringiensis against the box tree moth
Bacillus thuringiensis aizawai is effective against free-eating caterpillars such as the box tree moth (Cydalima perspectalis ), Winter Moth (Operophtera brumata), Cabbage White (Pieris brassicae; P. rapae), Cabbage Borer (Evergestis forficalis) and the oak processionary moth (Thaumetopoea processionea). The subspecies of the bacterium is the basis of our Plantura Zünslerfrei XenTari®. With this you can fight the box tree moth biologically - without any chemicals - and do not have to resort to means that can harm various insects in our environment in an unspecified way. You can find out how the application works, when and how often our Plantura Zünslerfrei XenTari® can and may be sprayed in our associated special article. You can also find general information on combating the box tree moth here.
Tip: If you are not sure whether your box tree (Buxus) is infested with the box tree moth, you can find out here how to recognize the borer.
Bacillus thuringiensis: effects on other organisms
The subspecies used by humans are highly specialized organisms that can therefore be used specifically to combat pests. Only if the bacterium from theWhen ingested by a suitable insect larva, the crystalline toxins match up with the host's digestive enzymes and receptors. On all other organisms that ingest Bacillus thuringiensis, its toxins have little or no effect. For this reason, there is no threat to bees or other pollinating insects. In general, however, all Bt preparations should of course be handled with the same care as any other pesticide.
Can Bacillus thuringiensis harm humans?
Even if humans and insect larvae don't have much in common, Bacillus thuringiensis is found everywhere in our environment anyway and the subspecies used as pesticides can only do something with the larvae of very specific groups of insects , the effect of Bt preparations on humans was examined in studies. The result was that the vast majority of subjects showed no reaction when exposed to Bacillus thuringiensis on a massive scale.
If you have now decided to use a preparation with Bacillus thuringiensis against pests such as the box tree moth, you will find all information about our Plantura Zünslerfrei XenTari®. here