The phenomenon that explains the trend seen in the data is that the mosquitoes' evolution has led them to develop resistance to the compound.
Explanation:
This is a very common factor that we can see in insects. The effect of DDT on the species will have different levels of impact. One is going to be more vulnerable to the compound that the rest. However, after many times of exposition to the compound, a few survivors will develop resistance to the compound and their offspring is going to inherit that resistance. Making them increase the resistance over time.
A country like China would probably be in Stage 4 of the population with the low birth rate and low death rate due to their economic power have technology to prolong and save their citizen from diease and condoms
I believe it is temperature or rainfall. All of the factors are improtant but temperature comes first, cuz the temperature can also determine the air, and soil doesn't make a difference. Longitude doesn't have to do with an ecosystem.