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Looking to control bagworms (Thridoptery ephemeraeformis) with Bt #679213 - Ask Extension


Looking to control bagworms (Thridoptery ephemeraeformis) with Bt #679213

Asked January 20, 2021, 8:48 PM EST

We get Bagworms on our arborvitae and they have done some serious damage. Because we are beekeepers we try to find a Bt solution. Thanks, Joe Hahn

Warren County Ohio

Expert Response

Good morning Joe,

Bt is a great choice for you as a beekeeper for controlling bagworm.  Timing is everything with using this product for these tricky caterpillars, so read your label very carefully.  I am attaching a great factsheet to help you understand the lifecycle and hope it is helpful to you. I don't see a particular question so I am not sure what exactly you need help with.  Are you looking for product?  Have you used it an had poor control?  Double clicking on the link below should lead you to the factsheet.

Bagworm and Its Control | Ohioline (

Make sure to store where there are no wild temperature extremes.  I made that mistake and pretty sure killed off the live bacteria in the product.

If your concerns haven't been addressed, feel free to write again with more detail :-)

Thank you for using the Ask Extension online service!

Kathryn McConkey-MGV Replied January 21, 2021, 9:39 AM EST
It is my very limited understanding there are numerous types of Bt. For example I use Xantari to attempt to control wax worm larvae on some of my bee equipment. I use a different Bt when throwing mosquito control granules into my water barrels. Or at least I think they are different. Please feel free to correct me.

Which ever Bt you suggest, if there are differences, do you have a brand to recommend? A supplier?

Thank you so very much,


On Jan 21, 2021, at 9:39 AM, Ask Extension wrote:

Joe Hahn Replied January 21, 2021, 2:20 PM EST

Hi Again

Yes, there are different strains of Bt that control different pests.  Btk (kurstaki) is what is used for control of caterpillars.  I have attached a couple more links that should help you understand a little better.  Brands names include but are not limited to, Thuricide, Caterpillar Killer, Dipel.  These can be found at garden centers and on Amazon.

The following link is from Buckeye Yard and Garden aka BYGL and you can scroll to the end for details on how this product works.  Again, timing is everything, so pay special attention to that part and also note that the caterpillar has to feed for awhile before they die, so this is not a contact spray-no instant gratification here.

Bagworm "Season" Begins | BYGL (    

This is a quote from another BYGL article (late summer)that you may find interesting, emphasizing the timing aspect again.  These are truly interesting critters: 

"The clock is also rapidly ticking down for standard insecticides to remain effective. Late instar bagworms can detect insecticide toxicants causing them to hasten pupation, but they do not die. However, they do stop feeding which leads to the perception they were killed. Early-pupating females produce fewer eggs, but they still produce enough to continue the infestation next season.

It's important to remember that bagworms may remain attached even if the caterpillars were successfully killed with an insecticide. They look just like bags with live caterpillars. The deception may lead to needless repeat applications, but they can only die once."

I hope this information covers your questions.  Thanks for your follow up quesiton!

Kathryn McConkey-MGV Replied January 21, 2021, 4:36 PM EST
Thank you for your help. I feel much better equipped for the upcoming season.

Take care and stay healthy,


On Jan 21, 2021, at 4:36 PM, Ask Extension wrote:

Joe Hahn Replied January 21, 2021, 7:30 PM EST
You are most welcome!

On Thu, Jan 21, 2021 at 7:30 PM Ask Extension> wrote:
Kathryn McConkey-MGV Replied January 22, 2021, 10:55 AM EST

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