Backyard Biology

Nature stories from my backyard and beyond

Nature Activities

Fun with Mosquitoes

Friday, November 4, 2011

For all the misery that mosquitoes cause us, it is only fitting that we occasionally have fun with them. At their expense.
Mosquitoes are a perfect subject for some backyard experiments. They are easy to find, they don’t take up much room, their requirements are minimal, and nobody much cares what you do to them.

For this activity, we will be using larval mosquitoes. Many people could not identify a young mosquito if their life depended on it. However, once you know what to look for and where to look, they are very easy to find. larvaeAll mosquito larvae live in water, mostly quiet, standing water. So any place you find standing water is a good place to look for the larvae. For my experiment, I collected more larvae than I will ever need by emptying the water from my bird bath into an aquarium. A quick look showed hundres of wrigglers squirming around in the aquarium. Mosquito larvae are called wrigglers because of their wriggling motion when they swim.
Some mosquitoes lay their eggs directly in water. The mosquito larvae that I collected from my bird bath were of this type. Others lay their eggs just above the water line on moist soil or vegetation. These eggs will lay dormant until a good rain or snow melt causes the water to rise and submerge the eggs, at which time the eggs hatch into the larvae. So another source of mosquitoes for your experiment is the soil or vegetation in these moist areas. Just place the vegetation in water and look for hatching mosquitoes. Sometimes these eggs will hatch in as little as 15 minutes of being placed in the water.

Since mosquitoes are at the least very annoying and at the worst the transmitters of some very deadly diseases, it is not surprising that much time and money has been spent on finding better methods of eliminating them. Naturally, some of these methods are more successful than others. I decided for this activity to test out a couple of the methods for eliminating the larval mosquitoes.
When I was a child, a common summertime sight was the mosquito control truck. The truck wold drive slowly along the backstreets spraying a fine mist of oil that would coat the surface of any standing water. Since the wrigglers need to breath air from the water’s surface, the oil would clog up their breathing tubes and suffocate the wrigglers.
Today, a common treatment for eliminating the larval mosquitoes are Dunks. Dunks contain a toxin produced by a soil bacteria, Bacillus thuringiensis, or Bti. This toxin attacks the digestive tract of the mosquito larva. The Dunks are placed in the water where they dissolve - releasing the Bti which the mosquito larvae take in when feeding.

Materials:

  • Mosquito larvae

  • small containers with covers
    (I used petri dishes for my experiment, but just about any container that holds water will work. Some suggestions are baby food jars or the containers that cupcake papers come in.)

  • oil

  • Dunks dunks

Instructions:

  1. Collect some mosquito larvae
    Look in any item that contains a little water such as bird baths, old tin cans, discarded tires etc.
    or
    Gather some sticks or vegetation in lowlying areas that is likely to get flooded. Any eggs on these items will soon hatch when placed in water. This is a good source of eggs if you need larvae in the winter.

  2. Place a number of larvae in three different containers. Label one “control”, one “oil” and one “Dunks”.
    petri dishes


  3. Set aside the container labeled “control”. Since you have not added anything to this container, these larvae should survive and you know that your growing conditions were adequate.

  4. Place a few drops of oil in the container labeled “oil” Make sure that the oil covers the whole surface of the water.

  5. Place a few granules of the Dunks in the container labeled “Dunks”. Only a very few granules are needed.

  6. Observe the containers for the next few days to see the effects of each treatment.larva

 

 

 

Notes:

I set up two containers for each treatment. The oil that I used was vegetable oil. As soon as the Dunks were added, the larvae began to feed on them.

Results:

After 12 hours:

  • 16 of 16 larvae in the Dunks container had died.
  • 7 of 10 larvae in the Oil container had died.
  • 0 of 11 of the larvae in the Control container were still alive.

After 2 days:

  • the three larvae in the oil container were still alive. These larvae were observed breating from the edges of the container. It is possible that the oil did not cover the suface completely and the larvae were able to find these clear spots to breathe.

Conclusions:

In my experiment, the Dunks containing the Bti appear to be more effective against the mosquito larvae because the oil may not have completely covered the surface of the water, whereas the Dunks readily dissolved and spread throughout the water.

Notes:

Experiments have shown that Bti is effective against the larvae of mosquitoes, black flies and some midges. There has been no health effects reported to mammals, birds and fish.