Can Mosquito Dunks Kill Fungus Gnats and Fruit Flies?

Mosquito Dunks

This is a question I am hoping to answer via some experimentation in the near future.

Some may recall that I tested out the nematode, Steinernema feltiae, as a fungus gnat killer last year and found that it was reasonably effective. The problem was that it was a fairly expensive solution, and generally would require ongoing applications in order to keep the gnats at bay over the long haul. Incidentally, I also tested Steinernema against fruit fly larvae, but I discovered one of the other limitations of this biocontrol organism – that being heat intolerance (at least I am pretty sure that’s what the main issue was).

And if those limitations aren’t enough – perhaps I should remind you of the fact that Red Worms have been shown to kill these nematodes as well!

I have read that some people have used ‘mosquito dunks’ successfully to control fungus gnats, so I’ve decided to try them out myself. The advantage of this approach (assuming it works) is that the dunks are a lot less expensive (especially when you consider how long a package will last in comparison to nematodes), and just generally less of a hassle to deal with.

I’m thinking that if I simply immerse a small chunk o’ dunk in a container of water (a full dunk is apparently enough to treat 100 sq ft of water area, so using a full one might be a bit of overkill – haha), then use that water to moisten an infested habitat, it should (hopefully) work.

I’m definitely not as optimistic about the effectiveness against fruit fly larvae, but you never know. Fruit flies are in the same Order (Diptera) as gnats and mosquitoes, but I don’t know if there is enough similarity. The particular strain of bacteria, Bacillus thuringiensis israelensis (say that three times fast!) is specific to dipteran pests, while other strains are used against beetle larvae, caterpillars etc – so that gives me some hope.

The key will me to make sure there is enough of this bacteria in the test systems that it ends up being ingested.

Anyway – I will be getting some experiments up and running in the next week or so, and will write a post once I am ready to roll.

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    • Barry Kopel
    • August 20, 2009

    DIY pop bottle trap

    Find a narrow-necked 2 or 3 liter soda bottle and fill the bottom inch or so with fruit juice, beer, soda, V8, apple cider, or vinegar along with a few drops of cooking oil or dish soap to break the liquid’s surface tension so any bugs that attempt to land will get caught in the liquid. Place the bottle in the area of infestation and watch all of the little fruit flies get trapped in the bottle or trapped in the liquid inside.

    DIY Bowl trap

    Don’t have any bottles? That’s ok, make this trap instead. Take any size bowl and cover the bottom with fruit juice, beer, soda, V8, apple cider, or vinegar (For other uses of vinegar, read how to make household uses for vinegar) along with a few drops of cooking oil or dish soap and then cover the top with plastic wrap. Poke several small holes in the wrap with a fork or thin knife and set it out in the area of infestation. The fruit flies will smell their way into the bowl and will be unable to escape

    • Bentley
    • August 21, 2009

    Hey Barry,
    I’ve had good success with bottle and jar traps containing apple cider vinegar, but I find that as a stand-alone solution they tend to fall short of the mark. The best solution would get rid of them at their ‘source’ (i.e. the food materials where the larvae are feeding). Not sure I’ll be able to do this using dunk liquid – but it’s worth a shot!

    • Rich
    • September 6, 2009

    Did it work?

    • Bentley
    • September 10, 2009

    Hey Rich,
    Unfortunately I still have not had a chance to do the experiment. Well actually, that’s not entirely true. I DID set something up, but it didn’t work very well as far as getting a thriving population of fruit flies goes, so I need to start over again.
    Will provide updates hopefully fairly soon.

    • Ann
    • September 27, 2009

    Bentley, I’d be oh-so-happy to send you some of my fruit fly population!

    • Scott Bryce
    • September 29, 2009

    I tried mosquito dunks to control fungus gnats, but it looks like I killed a bunch of worms in the process. No more mosquito dunk experiments for me. Beneficial nematodes are next on the list.

    • Bentley
    • October 8, 2009

    Thanks for sharing that, Scott – and sorry to hear about your worms. I have yet to run my own experiment (surprise surprise) but still plan to do so. If it turns out the mosquito dunk liquid does indeed kill off worms that will obviously not be good!

  1. I’d love to try the nematodes, but I live in a condo so I have no need for the huge amount of left over nematodes that I’d have.

    • brian
    • April 15, 2020

    can mosquito dunks and bits be added to compost bin and do they need water what type of water so they can kill the pests whilst composting. how often do i need to add them, b water i mean distilled or mineral or just normal type cool or warm water. i am trying to compost indoors and need to remove all pests and do they multiply and if so do i need to keep compost moist or allow to dry, how often to water,

    can i use them when sowing seeds or will they harm seedlings as the pest nibble the roots and all it keep getting is the two leaves and that is as far as it goes all the time and yes the seeds bolt and never get that far.

    i live in a block and have no garden.

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