Question

11. Farmers use pesticides to kill unwanted weeds and pest insects in their crops. Using the following steps of natural selection, describe how an insect population can become pesticide-resistant.

Natural selection (general process):

1 -- A population has genetic variation for traits

2 -- A new environmental pressure occurs

3 -- Individuals with adaptative traits survive and reproduce more than those without adaptive traits

4 -- The population has more adaptive traits (adaptive alleles) over time. Evolution has occured!

Apply the above steps to the specific case of pesticide resistance.

Answer 1

11- DDT works by inhibiting sodium channels in neurons of insects

1 Genetic variation with enhanced expression of cytochrome P450 may lead to the development of resistance

2- Due to environmental pressure created by the pesticides, new alleles may arise by a spontaneous mutation. Some of these may result in resistance towards the DDT inhibitory action on sodium channels

3- such individuals with enhanced cytochrome P450 or resistant allele of sodium ion channels may initially be present in few numbers in the population initially. These now proliferate.

4- Slowly the farmers will apply more amount of pesticide on the field to get rid of the resistant molecules. Because of these, the alleles may become selected again and again till they get fixed in the population.