Does anyone know if trichogramma wasps establish themselves in a particular area or must they be introduced to that area each year?

Thanks

My understanding is that trichogrammas eat bag worms and other caterpillar and worm-type pests.

I think you only need to release trichogrammas if you have one of those pests already.

So, if you don't have the pests, the trichogrammas don't stick around. (Same as ladybugs: no aphids, the ladybugs move on to where there is a food source.

I'm remembering this from reading one of Howard's books so maybe somebody who has first-hand experience will post.

Hope you get rid of whatever pest is interfering in your garden!
-Cara