Answer:
Due to no resistance.
Step-by-step explanation:
Most mosquitoes perish when DDT chemical was sprayed the first time because these mosquitoes are vulnerable to the DDT chemical and there is no resistance present in their body against this chemical. DDT chemical is an insecticide which is used against insects or pests that causes damage to human, organisms and crops. DDT was first synthesized in 1874 by the Austrian chemist named Othmar Zeidler.