How Bacillus thuringiensis Works: A Bug-Based Pesticide"

                                                 Fig: Bacillus thuringiensis 

Bacillus thuringiensis, or Bt for short, is a gram-positive, spore-forming bacteria that shows up on about 96% of mulberry trees. Gardeners and farmers love it because it’s a powerful bio-insecticide—it wipes out pests like webworms, caterpillars, mosquito larvae, black flies, beetle larvae, and fungus gnats. What’s really impressive about Bt is this: it contains a crystalline protein called Beta exotoxin, which has completely changed the game for organic farming and pest control. Think of Bt as a smart biological weapon. It goes after the bad bugs but leaves the good guys, like bees and ladybugs, totally unharmed.

 So, how does Bt pull this off? It doesn’t kill pests on contact. The bugs actually have to eat it. Here’s what happens:

 A caterpillar (or another hungry larva) munches on a leaf treated with Bt spores and proteins. Once inside the insect’s gut, the alkaline environment dissolves those protein crystals, turning them into active toxins. Beta exotoxin works by acting as an ATP analog, blocking the insect’s DNA-dependent RNA polymerase by competing for ATP binding sites. This basically shuts down RNA production, which leads to death or serious developmental issues for the pest. On top of that, the toxin breaks through the gut wall and makes the insect stop eating within half an hour. The pest starves or gets infected and dies within a few days .

            

                                                             Fig: Spraying Pesticide                            

     

Fig: Killed larvae

Bt isn’t one-size-fits-all. There are different strains, each targeting specific pests:

 1.      Bt subsp. kurstaki (Btk): This one knocks out lepidopteran larvae—so caterpillars of moths and butterflies. 

1.      2..Bt subsp. israelensis (Bti): This strain takes care of dipteran larvae, like mosquitoes, black flies, and fungus gnats.

  

Fig:Mosquito

                                                         Fig:Fungus Gnats                                     

1.     3. Bt subsp. aizawai (Bta): This one’s great against lepidopteran larvae, especially when pests start ignoring Btk.

                                                    Fig: Lepidopteran larvae

1.      4.Bt subsp. tenebrionis / japonensis: Works well on beetle larvae (coleopteran insects).

Why Farmers Use Bt Pesticides

1. Organic Certified: Farmers can use Bt in organic farming since it comes from a natural source.

2. Eco-Friendly: It targets only the bad bugs, so helpful insects like bees, butterflies, and ladybugs stay safe—good news for pollination.

3. Good for the Soil: Bt doesn’t mess up soil health the way synthetic chemicals do. It helps keep the soil fertile and its structure intact.

4. Fights Pollution: It breaks down quickly, so there’s less risk of polluting air or water. That’s a win for aquatic life.

5. Safer for People: Bt isn’t toxic to humans, so it’s safer for farm workers.

6. Better Harvests: Protecting crops from pests means less damage and more reliable yields

Tips for Getting the Best Results

 • Hit Young Larvae: Bt works best on young, hungry larvae (under 5 mm long). Spray early.

• Cover Everything: Make sure to spray all over the plants, including under the leaves, so larvae can’t avoid the toxin.

• Pick the Right Time: Spray in the late afternoon or on cloudy days. Sun and heat can kill Bt spores fast.

• Watch the Weather: If it rains hard within two days, spray again so it keeps working.

 Storage

Keep unopened Bt in a cool, dry spot away from sunlight. That way, it lasts longer.

 

                                                   Fig: Storage of Pesticides