Mosquitoes are a vector that transmits various forms of malaria. The fact that DDT was used to eliminate mosquitoes was ridiculous to begin with because it was hazardous to humans as well. The fact that some of the mosquitoes were genetically able to build resistance to the DDT would have resulted in mutations that could have been passed on to offspring. Following this, mosquitoes that have the resistance towards the DDT would have bred and eventually this would spread enough so that mosquitoes would become almost completely resistant to DDT, as the ones that are not would just die off.
