1. DDT and Mosquitoes
By: Bernadette

2. 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.

3. 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).

4. 3) Include an illustration or photograph of
the plant or animal (remember to
acknowledge your source).
Anopheles gambiae Anopheles stephensi
Image from: wikipedia.com Image from: lemur.amu.edu.pl
http://upload.wikimedia.org/wiki http://lemur.amu.edu.pl/share/ph
pedia/commons/e/e9/Anopheles_ p/mirnest/species_images/Anoph
gambiae_Mosquito.jpg eles_stephensi.jpg

5. 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. 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. 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. 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.