Fifty years ago, bed bugs were nearly eliminated in the united states by using of pesticides like ddt. today bed bugs are back in beds and theaters. ddt is no longer used due to environmental issues. pyrethrums are currently the top choice for bed bug infestations. pyrethrums are especially useful to us because they generally have a stronger effect on bugs than on humans and animals. some bed bugs had mutations in their genetic code which allowed them to survive the chemical pesticide and they produced chemically resistant offspring. how can this be explained?

Natural selection

Explanation:

What happened in the case of bed bugs and pesticides is natural selection at play. According to the natural selection theory propounded by Darwin, the environment selects for genes that able to withstand changes and organisms with such genes are able to survive, mate and pass on the selected gene to their offspring. Organisms without the selected gene gradually fades off from the population since they are not able to withstand the changes to the environment. Hence, after some considerable time, the desirable trait becomes dominant in the population.  

When DDT was in use, it was effective against bed bugs mutation in the genome of a few of the bed bug population conferred resistance against DDT on them. The environment selects this resistance trait because it is desirable. The resistant strains therefore, survive, mate and pass the gene to their offspring. After a while, bed bugs without the DDT-resistant gene die off the population while those with the resistant gene take over.

This might eventually happen to Pyrethrums too in the nearest future if natural selection law is to be considered.

americans began to notice growing differences between the northern and southern sections of the country. there were more people living in cities in the north, which made it more urban. more people lived on farms in the south, which made it more rural. while many people were farmers in the northern states, there were now other ways to make a living, such as working in mechanical cotton gins factories manufacturing cloth, tools and other goods. people in the north supported high tariffs on goods imported from europe because the extra cost encouraged people to “buy american” instead. in the southern states, planters did not like tariffs because they sold most of their production to europe and bought their tools from there as well. southerners believed the protective tariff was something that only northern factory owners keep their profits high. so the southern politicians came up with an idea. they would opt out. they would simply ignore the protective tariff. it was ‘null and void’ in south carolina. the state would not collect the taxes on goods imported into south carolina, no matter what the president said they had to do. this decision led to the nullification crisis.