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Natural Selection. DDT Resistance in Anopheline Mosquitoes. The spread of malaria can be controlled by controlling mosquito numbers. One way of controlling mosquito numbers is to use an insecticide like DDT. DDT. The malarial parasite is spread by anopheline mosquitoes. - PowerPoint PPT Presentation
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The malarial parasite is spread by anopheline mosquitoes
The spread of malaria can be controlled by controlling mosquito numbers
One way of controlling mosquito numbers is to use an insecticide like DDT
DDT
Not every mosquito will be killed each time we spray
Some will survive to repopulate the area, so… …we must spray frequently.
Random mutation may produce mosquitoes which are resistant to the effects of DDT…
…these are more likely to survive and pass on their genes to the next generation
NOTE
A resistant mosquito does not need to be totally immune to the effects of DDT…
… it may just be able to survive higher dose of DDT than ‘normal’ mosquitoes.
The next generation contains more resistant mosquitoes
Again, they are more likely to survive to reproduce, so…
…the proportion of the population which is resistant to DDT increases
With each successive generation…
…the proportion of the mosquito population which is resistant to DDT increases.
Spraying with DDT produces the selective pressure which favours the resistant mosquitoes.
Because they can resist the effects of DDT, the resistant mosquitoes are said to have a selective advantage