DDT and MosquitoesBy: Bernadette

1) Identify the plant or animal species.

Mosquito Anopheles gambiae

Anopheles stephensi

Both are the main vector of malaria in India (Anopheles stephensi) and Africa (Anopheles gambiae).

DDT was introduced to reduce malaria.

2) Describe the change that occurred within the species.

DDT is a pesticide. Introduced to kill mosquitoes and other insects that fed on crops and spread

disease.

Mosquito population decreased as it was used.

Eventually, they became immune to DDT and the population was able to increase again.

Survival through favourable characteristics that were passed onto offspring.

The use of DDT was stopped. Killed animals (e.g. birds and bats) through DDE (chemical that remains after

DDT breaks down).

3) Include an illustration or photograph of the plant or animal (remember to

acknowledge your source).

Anopheles gambiaeImage from: wikipedia.com

http://upload.wikimedia.org/wikipedia/commons/e/e9/Anopheles_gambiae_Mosquito.jpg

Anopheles stephensiImage from: lemur.amu.edu.pl

http://lemur.amu.edu.pl/share/php/mirnest/species_images/Anopheles_stephensi.jpg

4) Describe the change in environment that occurred.

Areas that were sprayed with DDT were harmful to mosquitoes, birds, fireflies and fish. Evident through decreasing numbers of birds in nests.

This happens through the food chain, not to the immediate organism. Therefore, the organism at the highest level has more toxic DDT in it.

However, it was not harmful to humans, therefore it was assumed that it would not be harmful to other animals.

5) Identify whether the environmental change was a physical or chemical

change. Chemical change in the environment.

6) Identify and describe the selective pressures acting on the organism as a result of the environmental change.

DDT was used to decrease population of mosquitoes, hence attempting to prevent malaria.

Once sprayed with DDT, the nerve cells of mosquitoes begin to fire, causing spasms from which they eventually die.

7) Explain how (4) led to (2) (show cause and effect).

Explain how the change in the environment led to change within the species. DDT sprayed on crops and people prevented mosquitoes

from coming and eventually killed them.

Through mutation and variations, mosquitoes were able to adapt so that they were resistant to DDT.

These mosquitoes survived, passing on favourable characteristics to their offspring.

8) Discuss whether you consider the example to be a form of macro-evolution or micro-evolution.

The change in mosquitoes from dying by the use of DDT to becoming tolerable is an example of micro-evolution. Species of mosquitoes have evolved from a common

ancestor.

These species are not affected by DDT.

Favourable characteristics are passed onto offspring.