> To clarify, Bacillus thuringiensis israelensis is used against Diptera > larvae, most commonly mosquito larvae but also fungus gnat larvae. ... > The form which kills caterpillars is different -- it's Bacillus > thruingiensis kurstaki. Jean is correct about the recommended subspecies of BT to use. I looked into what seemed to work for me. I seem to have used the "wrong" ones. I have used both: Bonide® Thuricide® Bacillus thuringiensis variety kurstaki. and Safer Brand Caterpillar Killer With BT - Active Ingredient Bacillus Thuringiensis. Var. Kurstaki > When mixed into the irrigation water for potted plants, one must > continue using it for at least 3 weeks to disrupt the fungus gnat's > life cycle. The stuff is destroyed by sunlight and the kind I used is supposed to be sprayed on the leaves. Thus, reapplication is needed above ground. My gut feeling (an inside joke for those who know how Bt works) is that this stuff lives longer than a week in the soil if watered in. I will go out on a limb with very little (or no) evidence to say I think the stuff is happier in the soil than it was in the bottle of concentrate and colonizes a never dry/frozen/extra hot/poisoned soil. Whether you reapply or not, it still takes weeks to do the job. I should try the "right" stuff sometime. I still would not trust the israelensis strains (Vectobac, Mosquito Dunks, Gnatrol, Bactimos, etc.) on my butterfly larva foliage. Kelly O'Neill http://www.bigbubblers.com/ and Big Bubble Magic(tm) at http://www.wetrock.com/ and Wet Rock Gardens Flower Farm 2877 N 19th Street - Springfield, Oregon 97477 U-Pick and more at the farm (open 9 to 6, Sun, Wed and Fri - from March thru Halloween) kellyo@wetrock.com - http://www.wetrock.com/