Thursday, March 3, 2016

Mosquitoes for Science Projects in Schools Part 2

Having made suggestions for science projects involving mosquitoes in my blog of January 20, 2016, I  set up a simple experiment to find out whether Aedes aegypti mosquitoes will lay eggs in water with or without dead leaves in it, in the shade or in the sun. 4 jars were set up accordingly. A second purpose was to follow the life cycle of A. aegypti, photograph the different stages and find out how long it takes from egg to adult. The experiment produced rather unexpected results, so may require some modifications, which I have suggested in an edited version of the previous blog post. I should have learnt a lesson here: "Don't suggest an experiment without trying it first", but had I done so, I mightn't have written the blog!

Jars set up to be placed in sun or shade
with or without dead leaves.
Which do mosquitoes prefer?
The jars were set up on Feb 7, 2016. As of Feb 9, there were no eggs.

March 3, 2016. Still no eggs!
    March 3, 2016 - still no eggs, nor larvae. I have decided to abandon this experiment and comment on why it didn't proceed as planned.
1. The week following setting up the experiment, it rained every day and there was little sun. The jars put in the sun filled up and overflowed with rainwater. (I poured off some of it.)
2. I may have put too many leaves in the jars. As they rotted, they depleted the water of oxygen. Whether this would affect larvae, I don't know, as they do come to the surface of the water for air, but it would certainly make it more difficult to see them.
3. Leaves fell into the jars without dead leaves, so they were no longer accurate controls. Algae started to grow in the jar without dead leaves in the sun. This would also provide food for potential mosquito larvae.
4. The failure of this experiment doesn't mean there were no Aedes around. I observed larvae in other containers, such as a bowl I use to water orchids. I disposed of most of them, but kept a few in a jar with a lid so that I could confirm that the adults, when they hatched out, were indeed Aedes, and they were.
5. Another drawback to this experiment is that young larvae are so small they are hard to see.
Final stage larvae of Aedes,
barely 1 cm long.

            I had suggested this experiment for primary school children, but it might be more suitable as a project for students of biology doing CSEC or CAPE (Caribbean exams.) It would be useful for them to have access to a microscope or a binocular microscope so that they could observe young larvae.
             A more suitable activity for primary school children would be for them to hunt for existing mosquito breeding  sites and record the conditions under which the larvae of Aedes were found. A follow-up activity, ridding the environment of these breeding sites, needs to be an on going one.  My own observation is that Aedes are more prevalent after about a week of fine weather following a period of heavy rains.
      Another source of confusion in relation to mosquitoes is that there are so many similar species, identifiable more by their habits than appearance. Aedes breeds close to human habitation, not  in forests - the Cockpit Country is full of mosquitoes, none of them Aedes. Mosquito larvae found in bromeliads or Traveller's Palm are unlikely to be those of Aedes, and it is hard for the casual observer to distinguish between the larvae of different species of mosquito.
        However, the behavior of the adult Aedes is well known to us. We know they are hard to swat and quickly fly off, while another species sitting on your arm feeding will allow you to swat her. The reason is that the latter must fill her stomach from her first victim, while Aedes will fly off and feed off as many people as necessary to fill her stomach. However, if Aedes catches you sleeping, you could well be her only victim. If Aedes feeds on the blood of someone with Chikungunya, Dengue or Zika, the viruses will remain in the mosquito and can be passed on the eggs.  Within 8 - 10 days of hatching, the eggs will give rise to adults which will infect humans when they feed on them.
     Our best defense against these pests continues to be vigilance in removing the breeding sites of Aedes around our homes, schools, business places, churches and other meeting places. For other breeding sites, such as potholes in roads, we need to put relentless pressure on the authorities.

No comments: