Mosquito Dunk Fruit Fly Fungus Gnat Update

Fruit Fly Larvae
Fruit fly larvae – up close and personal

Back in the middle of August (oh how time flies!) I wrote a post about my plans to test out ‘Mosquito Dunks’ as a means of getting rid of fruit flies and fungus gnats in a worm bin (see “Can Mosquito Dunks Kill Fungus Gnats and Fruit Flies?“). Well of course – me being me – while I DID get around to setting up some bins outside to attract some fruit flies, I failed to actually get going with the experiment until some really cold fall weather finally made me realize I needed to act fast or risk losing my outdoor fruit fly ‘culture’.

So, being the smart fellow that I am, I decided to bring a culture of fruit flies indoors where my systems were happily chugging along, fruit-fly-free! Oh well – I always enjoy ‘taking one for the team’ in order to make a learning experience out of it, so now that I am enjoying a serious infestation of fruit flies in my basement, I know it’s finally time to get started!

I’ve set up a bunch of new apple cider traps, and the other day I started brewing my mosquito dunk water. I’ve decided to proceed somewhat cautiously with this experiment – largely due to the fact that someone left a comment on the other post (mentioned above), indicating the potential for actually harming the worms. While I’m not 100% convinced that this will be the case, I also don’t feel like being so reckless with my worms’ well-being as to simply starting pouring the stuff on my indoor beds. I might as well make sure it’s even going to kill the larvae before taking the risk of inflicting harm on my dear wormies!

As such, the original fruit fly culture container brought in from outside has become ‘ground zero’ for my experimentation.

Fruit Fly Container

This container has a piece of corrugated cardboard and a virtually-liquefied cucumber in it. There are lots of fruit fly larvae visible on the cardboard (such as those ones in the first pic) and until recently there were also lots of adults. I released them all when I opened the system to apply the dunk liquid A) accidentally and B) because I am trying to see if the larvae will mature into adults once their food source has been soaked in ‘dunk juice’ (Brain wave! If all this works out for me – I should really think about marketing my new fruit fly killer as ‘Dipteran Dunk Juice’! Haha).

To apply the liquid I used a small syringe and slowly soaked all zones where the larvae were visible – I made sure to move any run-off around the entire container as well.

So far so good – all I noticed today was the presence of two tiny adults. Fruit flies develop VERY quickly, so I’m hopeful that this is a positive sign. Many of the larvae DO still seem to be moving around, but we’ll see how they are doing in another day or two. The bacterium in ‘Dipteran Dunk Juice’ (TM) causes these larvae to stop feeding – so it’s not like some sort of instant poison or anything like that.

If it looks like the larvae are dying off, and no more adults are being produced we’ll move on to ‘phase II’. I’m still not planning to put the liquid on my actual beds yet – first I will set up a small experimental system, perhaps with a chunk of rotten fruit (or fruit-juice-soaked cardboard) in it, along with some worm bin material and a small number of worms.

Stayed tuned!

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    • Cole
    • November 5, 2009


    Great website!!! I’m a vermicomposting newbie; I started with 150 worms in April 2009, and now I have a thriving herd thanks to what I’ve learned here at RWC!! I’ve read every article that you have posted, but I must say I’m REALLY looking forward to your updates on the mosquito dunk experiment. Fruit flies have taken up residence in my basement and my wife will throw a fit (along with my worm bins) if she ever finds out about it (luckily she doesn’t venture into the basement too often).

  1. I’m really interested to see how this turns out. Our local mosquito abatement program uses chunks of the mosquito dunks in local ponds to knock out the population without harming wildlife. They even put pellets in the grinding stones common around here at Native American village sites. I have a problem with them because I brew my own vinegar and kombucha as well as worm farm inside the house. Luckily we usually can keep it under control by immediately putting food away, keeping food in the bin covered and monitoring feeding levels, and taking the trash out often.

    • Bentley
    • November 7, 2009

    I am definitely interested to see how it turns out as well! If it actually works, I’ll be very excited that’s for sure!

    COLE – Are you on my newsletter email list? I just sent out a newsletter issue all about fruit flies, with a handful of suggestions for getting rid of them. Feel free to drop me a line if you didn’t get that I I’ll forward you a copy.

    • Selene in Florida
    • November 9, 2009

    Okay, if you don’t know if this is gonna be lethal to your worms you’re gonna have to try it out on a few to see, right? So tell me, fellow lover of wormies… just how are you gonna pick out the ones to be possibly sacrificed and how do you think it’ll make you feel to see that you’ve killed some of your babies, if worse comes to worse?
    I know you’re doing this for the greater good and for all of us that follow your blog with great interest, but seriously… I just couldn’t do it myself. I’m WAY too much of a wuss and WAY too attached to my squirms.
    WOW! I’m not normal, am I?

    • Bentley
    • November 9, 2009

    Hi SELENE – I was wondering if my post would end up eliciting any disapproving responses. This is an interesting issue in general – something worthy of discussion in its own right.
    I am still not 100% sure what I am going to do – I have yet to see any real indication that the dunk liquid is even harming the fruit fly larvae.

    Speaking of which, while I totally understand where you are coming from here, my question to you would be – have you ever harmed invertebrates on purpose?

    Ever smacked some mosquitos? Killed some ants? Drowned some slugs?
    Its funny how nobody is concerned about the poor gnat and fruit fly larvae here!

    OK, so I am just having some fun with you Selene. I can assure you that if I DID end up setting up a small test system with worms, there would be no specific “selection” process. I would simply grab some material (containing worms) from one of my bins.

    Anyway – let’s wait and see if my fruit-fly mass-murder experiment works first!

    • Selene in Florida
    • November 10, 2009

    Okay Bentley, you made your point, sort of. BUT…all the invertebrates that I’ve killed on purpose were NOT creatures that I’ve welcomed into my home and kept warm and well fed. They’re not ones that I’ve worried about when something went amiss with their environment. I HAVE welcomed black soldier fly larvaes in as well, so if you had been trying to kill those I would’ve balked also!

    Anyway, like you said, we’ll just wait and see how it goes. And I also agree with how you’d ultimately do it. I’d just grab a handful (while I looked the other way), and use that too.

    • Bentley
    • November 10, 2009

    Interesting way of putting it, Selene (the “warm and well-fed” part made me smile), and again I DO understand where you are coming from. I don’t want to seem like I don’t care at all about the welfare of my worms, and my intention is not to start a debate (although, as mentioned, I do find all of this very interesting).
    When it comes down to it, I find it very hard to believe that anything from a mosquito dunk could actually kill a worm – the bacteria are very specialized for a certain group of insects, and of course there can’t be any sort of toxic chemicals in the dunks since they would either kill the bacteria, and/or kill other creatures in the water (apart from insect larvae) thus not living up to the promise of being ‘harmless’ to other organisms.

    • Julie
    • November 14, 2009

    I use the dunks by just adding a portion of them to a watering can and then sprinkle the bin a little each time I mix up the bed. Works wonderful, I am told it is totally natural and…my worms are fine.

    • Bentley
    • November 20, 2009

    Hi Julie – sorry for delay responding. That is REALLY interesting. So you are saying that this has reduced a fruit fly (or gnat) population that you already had? Or do you mean that it seems to be preventing them from becoming established in the first place?

    I still don’t seem to be having much luck with dunk water myself – definitely not too optimistic at this point.

    • Sora
    • September 1, 2010

    So did you ever get it work? or find another way to kill off flies? I have a huge infestation in mine and I HATE them! But, as you said, I am worried about hurting my worms in the process… Let me know!

    • Bentley
    • September 3, 2010

    Hi Sora – my results were not promising. I saw no evidence that it was working on the fruit fly larvae in my special test system.

    My approach for fruit flies is as follows:

    1) vacuum up adults daily
    2) remove excess food and only feed with bedding
    3) fruit fly traps – small amt of cider/wine vinegar with drop of dish detergent in jar. Cover with Saran wrap and punch small holes with fork.

    • Sora
    • September 9, 2010

    Aw, bummer. Well I will try your new approach then. Thanks!

    • Dee
    • April 10, 2021

    I have poured tons of mosquitoes bites in my worm bin, because of an investation and they seem to be doing okay.
    I have also poured a lot of insect DE and that didn’t go to well. I lost a lot of my population even thou it stated it wouldn’t harm the worms.
    Just to be clear the mosquitoes bites just effect the gnat larve, they do nothing to the adult fruit flies. So if you have plants they will go seek out any other place they can. It took me months to clean house.
    start with a small amount and increase the amount as your confidence build that you worms are not being harmed. In order for the bits to work thou, the gnats can not be allowed to access any food that dosnt have the mosquitoes bites.
    Hope this helps

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