Greetings,

I don't think you should be considering an insecticide to solve your problem. I would suggest learning to accept the gnats - they are basically ubiquitous and you were strangely lucky not to have them already.

You can also try creating new, clean cultures for your isos.

Insecticides are not fine instruments - they take down an entire spectrum of organisms the vast majority of which are not your intended target. They are not a proper tool for vivarium husbandry.

 

Thank you for your comment - I should perhaps clarify a couple things:

Though the preponderance of evidence I have read would suggest Bt (a bacteria not a traditional pesticide) has minimal to no impact on non-target species, I still do not intend to directly apply it directly to vivariums. I do intend to use it in my isopod cultures as an alternative to discarding them. Bt degrades below effective concentrations fairly quickly, so I am not particularly concerned about a hypothetical cross contamination if I add isopods to a new vivarium eventually. I also should mention I keep mostly reptiles in my bioactive enclosures, so the one or two studies that mention possible toxicity to developing tadpoles at concentrations much higher than would be possible in the conditions I am describing don't spook me.

We could get into a debate about the use of Bt in a vivarium setting, but that's sort of outside of the scope of what I'm looking for here, which is application instructions from someone who has used it before (there are several accounts on this forum of successful use, just light on the actual information of how they mixed it up).

 

Bacillus thuringiensis is some amazing stuff. I haven't used it yet, but studied up on it last year. Last year I was too late, but this year I have no worries about the cabbage worms. There are at least several different strains. The ‘isrealensis’ type targets immature flies and mosquitoes. I will be using the ‘kurstaki’ strain shortly on my brassica crops. The kurstaki strain targets caterpillars. The cabbage worm is brutal in my area.

Are you aware that bt can establish a live culture within the soil? In addition, it does not readily rinse away. Even after a heavy rain, it is still found concentrated in the top several inches of soil.

As far as mixing and application, there are different types, and different brands. I would follow the mixing directions that come with the brand you may select. Application is all on you. You want to use it in a way it is not designed for. I'm not saying there's anything wrong with that, just that it's not very likely that anyone has used it that way. Generally, it would be sprayed directly on the plants you are trying to protect. The bugs take a few bites, and very quickly stop feeding. Death can take hours to days. In my veggie garden, I anticipate having to re-apply weekly, and after heavy rains. The rain will wash it off the plants, where it may or may not take up "permanent" residence in my soil. That won't benefit me, as cabbage worm lay their eggs directly on the plant.

I think bt is amazing stuff for how it targets the problem, and lets everybody else live through the attack. It doesn't harm desirable bugs, like earthworms, pollinating honey bees and butterflies, or even the desirables like springtails and isopods are supposed to be entirely unaffected by it.

That said, I would still worry about using it around frogs. I would also be nervous that it could very well establish a "permanent" residence in your culture's substrate. Cross contamination would worry me. A mistake could plausibly wipe out your fruit fly cultures.