Do colonies of water daphnia prevent mosquito larvae ?

[SteveMid]

I have a tub outside in the garden with rain water in that originally I used to use to occasionally harvest mosquito larvae to feed my aquarium fish. A couple of years ago I put a culture of water daphnia in it and have farmed these ever since. They live through the winter and bloom to a larger population in spring and summer. However, since I added the daphnia I have not seen a single mosquito larvae. There are midge larvae in there but never a mosquito larvae. Is this a known phenomenon? Surely something is putting the mosquitos off laying their eggs?

 

[Fishfur]

It’s not something I’ve ever heard of. Daphnia are filter feeders so they shouldn’t have any effect on skeeter larvae, which breathe air rather than water & generally the insects are not fussy about water so long as it’s quiet & still.

It may be something else that’s different about the water conditions that’s making the tub unattractive to the skeeters.

 

[dw1305]

Hi all,

It may be something else that’s different about the water conditions that’s making the tub unattractive to the skeeters.

You only get Mosquito larvae as pioneer species in new "ponds" that are organically rich. I think by the time it is suitable for Daphnia it has matured past that stage.

cheers Darrel

 

[Aquahorti]

Interesting question.
My initial thought was that the Daphnia was out competing the mosquito larvae as they are more or less feeding on the same food items in the water, but I was unsure if that was the case so I thought I would look in the literature to see if anyone had look at it before.

It turns out that D. magna does indeed help reduce the number of larvae that reached maturity under lab conditions (see https://www.researchgate.net/profil...WQiLCJwcmV2aW91c1BhZ2UiOiJwdWJsaWNhdGlvbiJ9fQ) but I have not been able to find anything that supports or refutes that D. magna will prevent/deter mosquitos in laying their eggs in the water. I have found an article that states that they can ingest items up to 1400 micrometers (see https://www.sciencedirect.com/science/article/abs/pii/S0166445X24001462), but that their typical food items are far smaller (0,1 to 30 micrometers). The eggs and newly hatched larvae are typically bigger, but still within the range where D. magna can ingest them. That does not prove that they will, but it could be possible.

 

[SteveMid]

Interesting question.
My initial thought was that the Daphnia was out competing the mosquito larvae as they are more or less feeding on the same food items in the water, but I was unsure if that was the case so I thought I would look in the literature to see if anyone had look at it before.

It turns out that D. magna does indeed help reduce the number of larvae that reached maturity under lab conditions (see https://www.researchgate.net/profil...WQiLCJwcmV2aW91c1BhZ2UiOiJwdWJsaWNhdGlvbiJ9fQ) but I have not been able to find anything that supports or refutes that D. magna will prevent/deter mosquitos in laying their eggs in the water. I have found an article that states that they can ingest items up to 1400 micrometers (see https://www.sciencedirect.com/science/article/abs/pii/S0166445X24001462), but that their typical food items are far smaller (0,1 to 30 micrometers). The eggs and newly hatched larvae are typically bigger, but still within the range where D. magna can ingest them. That does not prove that they will, but it could be possible.

Thanks for your reply @Aquahorti and time to look into this - it is interesting that it has been studied in the lab. I am sorry for my late answer but I have only just seen your post.
It is very timely, however, as after I received the initial responses on 13th apr, I decided to see what would happen if I tried to increase the food source (algae) in the tub so I drained half the tub then filled it with my aquarium water from my weekly water change and then added some NPK fertiliser for good measure. Sure enough yesterday, i observed a few tiny mosquito larvae. I guess it doesn’t really show whether the adults know whether there is enough food in the water to then lay their eggs or whether relatively “clear” water prevents the larvae from developing but it’s kept me occupied for a few days 😀

 

[tiger15]

I place a window screen over my outdoor daphnia culture tub to keep out mosquito. Even a small gap or hole in the screen can invite mosquito to enter to lay eggs as they can smell water. Even if a dense culture of daphnia can outcompete with mosquito larvae to some extent, daphnia go through dormancy in hot summer months leaving opportunity for mosquito larvae to thrive.

 

[Aquahorti]

Interesting, I wonder what kind of mosquito it is you have in your garden/general area that thrives in those conditions.

A quick search and read through a few articles leads me to think that your observation might be of interest to the team behind third article I have linked to (look below).

The optimal temperature for D. magna to live at seems to be somewhere between 20˚C and 25˚C (see The temperature‐size rule in Daphnia magna across different genetic lines and ontogenetic stages: Multiple patterns and mechanisms - PMC ), so based on that you should probably try to ensure that your outdoor tube is at least partly shaded from the sun in the middle of the day (or dig a deep hole and have a container deep enough that the cold soil acts as a cold reservoir) but they will do fine up to at least 30˚C.

This study (see Larval diet and temperature alter mosquito immunity and development: using body size and developmental traits to track carry-over effects on longevity - Parasites & Vectors ) does seem to indicate that although this type of mosquito larva does well in the range up to 30˚C it is a downwards trend just as with D. magna).
The last study I link here (see Temperature during larval development and adult maintenance influences the survival of Anopheles gambiae s.s - PMC ) although that is on a different species, indicates that this type of mosquito does not fair well in water that have a temperature of 35˚C. I should mention that the species of mosquito used in the two last studies both are tropical/subtropical species so I would expect them to have a high temperature tolerance.

I should mention that I have never ‘grown’ D. magna in tubs outdoor, only in small tubs and aquariums inside, back when my wife was going through her Betta breeding phase, as they seemed to have a higher breeding frequency when D. magna was part of their diet. I did however spend most of my free time between the ages of 6 and 14 out in nature looking a fresh water systems as part of my preparations to study biology so have quite a bit of experience and observations from nature. I ended up being a Mathematician and later a Physicist, so I can not claim any formal academic authority within the realm of biology.