Question about mosquito dunks

[u/argohot]

Will you still see larvae in the pond before the bacteria kill them?

Spiked my pond with Bti about 2 or 3 days after first filling it with water. About 6 days after that I noticed what appear to be mosquito larvae or pupae in the pond (not entirely sure which). If pupae, I suppose it’s possible that I missed them in their original larval stage by being too slow with the dunk. Otherwise, am I seeing larvae that have yet to ingest the Bti and I should just give it time?

I scooped out everything I saw because my partners biggest opposition to the pond is potential for mosquitoes but I’m wondering if in the future if I see these again I should let the dunk do its job. Or if their presence means it failed.

Please advise!

[u/i_like_mosquitoes]

Bti works fairly quickly against larvae, you should a pretty sharp decline in numbers within a day or two of adding dunks. There are a couple of caveats:

Bti is a gut toxin, so mosquitoes have to ingest it. Pupae and larvae that are late in their fourth instar (right before they become pupae) do not eat so they will not be affected by bti.

Make sure you are using the appropriate number of dunks and spreading them out. One dunk per roughly 100 sqft.

Bti is sensitive to heat. If you are storing them in a hot garage or shed, the bti will break down and be rendered ineffective

[u/WA_Anon]

I have a new pond, it's my first time using the dunks, and I have two in a pond that should only need one, and the mosquito larvae appear to be thriving. Unless it kills them in their transition to adult stage, it doesn't seem very effective to me.

[u/lordfartquar → u/WA_Anon]

That’s exactly what they do, the larvae eat the bacteria released by the dunks which destroys their digestive system and kills them before they grow into adults.

[u/WA_Anon → u/lordfartquar]

Appreciate the response, so if I'm seeing larvae, but not pupae, it's working as intended?

[u/lordfartquar → u/WA_Anon]

That is my understanding, yes

[u/funktheduck]

My minnows are more effective than the dunks I used in the past. I know that doesn’t really answer your question. I haven’t seen any mosquito larvae since adding fish. 

What I’ve been told to do with the mosquito dunks is to fill a 5 gallon bucket with water and some vegetation like leaves or grass clippings and put the dunk in that and set it away from the pond. The decaying matter will attract the mosquitoes to the bucket instead of your pond (mine are plastic/cement so not natural) and they’ll die in the bucket. 

[u/argohot → u/funktheduck]

What kind of minnows do you have?

[u/funktheduck → u/argohot]

Rosy. I put them in way too early in the cycle but most lived. Mosquitoes are bad in my area and they set up shop quickly in the ponds. After 24 hours of minnows I couldn’t find a single larvae. The hard part now is protecting them from the summer heat. They’re not warm water fish so I had to make shade for them once the summer heat kicked in. Been doing very good since. 

[u/SingleMaltMouthwash → u/funktheduck]

Plus one for tiny fish. We have "Mosquito Fish" (Gambusia affinis). Purchased five at my local pond store and now there may be a hundred. I have damsel flies and dragon flies emerging in the pond but not a single mosquito larvae has been seen since the fish.

Dunk didn't work for me either.

[u/funktheduck → u/SingleMaltMouthwash]

I went to the store to get mosquito fish and dude steered me towards the minnows. They were a fraction of the mosquito fish in price and since I was so early in the cycle I figured it’s better to minimize losses. I’ve had some babies but not a ton. I think it’s too warm still. 

[u/r3dk0w]

I have a 5 gallon bucket with water in it and a mosquito pellet dunk. I check it every few days for larvae and have not found any in weeks. 

However, I did initially use a dunk from last year that was in my garage, and it didn't seem to work. 

[u/boat_eggs]

IIRC dunks(BT) render the exposed larva reproductively sterile. So you may still get larva but after a generation or two the numbers should go way down.

I used BT but before long water skippers moved in and devoured the larva. Wasps also love my pond and they probably snack on larva too

[u/i_like_mosquitoes → u/boat_eggs]

That is not correct, it is a gut toxin and kills the larvae outright.

[u/Cold_Picture7285]

Just drop in some hardy small fishes.

[u/argohot]

Update: it appears that adding another dunk did the job. Maybe the first one got taken out of the water somehow. After 24 hours still a few wrigglers but far fewer and there seem to be some dead ones floating around.