Host Insects

Some of the insects that are targeted by B.t. are cabbage loppers, tent caterpillars, moths, tomatoes, hornworms, gypsy, beetles, black flies, mosquitoes, etc…

What Pests does B.t. control?

Bacillus thuringienis is most effective against the immature stages or larvae of insects but not the adult stages. There are many strains of B.t., and each is most effective against certain insect pests. Some of the strains are as follows.

• B.t. var ‘tenebrionis’ – larvae of elm leaf beetle.
• B.t. var ‘israelensis’ –  black flies, and other flies., larvae of mosquitoes.
• B.t. var ‘kurstaki’ – many species of caterpillars.
• B.t. var ‘San Diego’ – larvae of elm leaf beetle.
• B.t. var ‘aizawa’ – to control larvae of wax moths and other moth species.

How to Apply Bacillus thuringienis?

• Choose the right product, i.e. the proper strain, of B.t. for the insect to be controlled.
• Avoid water that has a high pH when mixing B.t. sprays because water with a high pH will reduce the effectiveness of B.t.
•  B.t. spray must be used within 12 hours of mixing.
• Applications should be timed to correspond with the most vulnerable life stage of insect pests.
• Applying a spreader/sticker to the tank mix improves the effectiveness. Spray application should be applied if heavy rainfall occurs within 8 hours after the spray is applied.

What are the Advantages of B.t.?

• Harmless to humans and other mammals.
• Potent effects targeted insects quickly.
• Biodegradable.

What is the Disadvantage B.t.?

• When applied in liquid or spray form B.t. degrades because of the sunlight, most formulations persist on the plant’s foliage (leaves) less than a week following application.
• Can easily be removed from the leaves’ surface by the rain and the wind.
• Needs to be reapplied to be effective.

Forms of B.t.

B.t. comes in either dust, sprays, pellets, or granules.

Where to use B.t.?

B.t. can be used on ornament plants and crops.

Additional information

•  There are many types of Bacillus thuringiense each targeting different insect groups.
• B.t. is broken down in acidic soils and the sunlight.
•  B.t. has been around from early as the 1950s.
• One report has it that “B.t. is highly toxic to the honeybee”.
•  There is no soil leaching with B.t., B.t. remains in the first top inches of the soil.

Caution

Before using this product read and follow the manufacturer’s label for the best results

10 Frequently Asked Questions (FAQs)

1. What is Bacillus thuringiensis (Bt), anyway?
Bt is a naturally occurring soil bacterium that’s used as a biological pesticide. It produces proteins that are toxic to certain insects—but safe for humans, pets, and most beneficial bugs. It’s one of nature’s own pest control tools!

2. How does Bt actually kill insects?
When susceptible insects (like caterpillars or mosquito larvae) eat Bt-treated leaves or water, the Bt proteins react with their gut lining. This disrupts digestion and causes the insect to stop eating, eventually killing it within a few days.

3. Is Bt harmful to humans or pets?
Not at all. Bt only affects certain insects with specific gut biology—it doesn’t harm humans, dogs, cats, birds, or other mammals. That’s why it’s a favorite among organic gardeners and eco-conscious homeowners.

4. What types of pests does Bt control?
Bt targets specific groups of pests, depending on the strain:

• Bt kurstaki (Btk): Kills caterpillars like cabbage loopers and tomato hornworms.

• Bt israelensis (Bti): Kills mosquito, black fly, and fungus gnat larvae.

• Bt tenebrionis (Btt): Controls beetle larvae like Colorado potato beetles.
  Choose the right strain for your pest problem!

5. Will Bt hurt bees, butterflies, or earthworms?
Nope! Bt is highly selective. For example, Btk only affects caterpillar species that eat the treated leaves—so adult butterflies and bees aren’t affected, and earthworms are totally safe.

6. How do I apply Bt in my garden?
Bt is usually sold as a liquid spray or powder. Just mix it according to the label and spray it directly on your plants’ leaves. Make sure and get complete coverage on the leaves undersides where pests hide and feed!

7. How long does Bt stay active after application?
Bt breaks down quickly in sunlight and rain—usually within 3–7 days. For ongoing protection, especially during pest season, you may need to reapply weekly or after heavy rain.

8. Can Bt be used in organic gardening?
Yes! Bt is approved for organic gardening by most standards, including OMRI. It’s biodegradable, safe for the environment, and doesn’t leave chemical residues on your crops.

9. Do insects become resistant to Bt over time?
It’s possible. Just like with chemical pesticides, overuse of Bt can lead to resistance in some insect populations. To prevent this, rotate pest control methods and only apply Bt when necessary.

10. Is Bt safe to use around edible plants like herbs and veggies?
Absolutely. Bt is safe to use on fruits, vegetables, and herbs. Just follow the label instructions and observe any pre-harvest interval if listed (usually it’s very short or zero).

Conclusion

Bacillus thuringiensis has proven that it can get the job done, this is a great product that can help to bring garden insect pests under control. It has also been reported that B.t. is used widely in the agricultural field. No human health hazard from using B.t. has been reported, B.t. has also been used near rivers and lakes and is not a threat to wildlife. I believe that a product like this is worth the investment so if you are in the market for a product of this nature then Bt is the product for you.