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Mosquito Dunks For Gnats and Fruit Flies – Revisited

Back in August of 2009 I decided to test out “Mosquito Dunks” as a potential way to get rid of fruit flies and fungus gnats.

My (somewhat vague) memory of the experiment(s) was that there wasn’t an obvious reduction in abundance of gnats and/or fruit flies as a result. BUT, I have recently come across at least a couple of mentions of success with this method from others, so I’m eager to test it out again (and compare to my parasitic nematode experimentation).

Here’s what I really like about Mosquito Dunks (in comparison to nematodes):

Dunks release the bacterium, Bacillus thuringiensis israelensis (no wonder they call it “Bti”?? lol) gradually over time. Bti produces a toxin that kills various dipteran (“true fly”) larvae, while not causing any harm to various other life forms, including worms, humans, and pets!

My innner “biology geek” is still a little uncertain about my chances of success with fruit flies, to be honest. Gnats and mosquitos are in the same broad grouping (sub order) within the order Diptera – called Nematocera – while fruit flies (along with house flies, soldier flies etc) are in the sub order Brachycera. I’m still not 100% sure that Bti targets brachyceran larvae.

Only one way to find out, I guess! 😉
(And like I said, others have reported success so I’m still somewhat optimistic)

My first test method is pretty basic. I simply broke off a small chunk-o-dunk (I had way too much fun writing that! lol) and dropped it in a small container of water.

Now I’m letting it sit for 2-3 days before I add the liquid to a test system containing loads of gnat and/or fruit fly larvae. I’ll then fill the container up with more water and repeat the process a few days later. Naturally, it will be important to balance all this liquid with some dry bedding (in my ziploc test systems) as well.

I may also just try crumbling up a dunk and sprinkling it into one or more systems. The obvious advantage of that approach is that I won’t need to keep adding more liquid to the systems – but the potential downside is that I may use up my remaining dunks more quickly.

As always, I will keep you posted on my progress, so do stay tuned!

Written by Bentley on February 24th, 2017 with 5 comments.
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Get your own gravatar by visiting Paul from Winnipeg
#1. February 27th, 2017, at 5:28 PM.

Watching with interest Bentley. I’ve tried this before with mixed results, but I didn’t wait as long as you before using the water. Maybe that will make a difference.

Hope I didn’t send 2 comments by accident. Haven’t seen my last one for a few days.

Get your own gravatar by visiting Bentley
#2. February 27th, 2017, at 10:14 PM.

Hey Paul – good to hear from you. Apologies for the issue with the last comment. I didn’t notice it come through and for some reason it was held for moderation.

When you say “mixed results” does that mean you did see SOME indication of it working?

Get your own gravatar by visiting Bobbi
#3. July 4th, 2017, at 11:24 PM.

I’m curious about the results of this experiment. 🙂

Get your own gravatar by visiting Gary Scott
#4. February 4th, 2018, at 9:00 AM.

I grow using Aquaponics. I use Red Worms in the grow beds to eliminate fish solid waste which works great BUT the fact that this is a wet enviroment Fungus gnats are an issue. My question is will Bti (Bacillus thuringiensis israelensis) kill my worms or the benificial bacteria from the fish waste?

Get your own gravatar by visiting Bentley
#5. February 8th, 2018, at 3:04 PM.

Hey Gary
I know of NO evidence to suggest that Bti will harm worms. I have played around with the dunks (adding water the dunks have soaked in or even crumbling the dunks and adding them directly, with no issues). I doubt it will harm beneficial bacteria (who are likely better adapted for that environment) either. Just my 2 cents worth!

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