What are some factors that might cause changes in the population of grasshoppers?

The factors that might cause changes in the population of grasshoppers are: 

Weather - dry weather increases the probability of egg survival, and speeds up spring hatch, and promotes the development of nymph and adult feeding. Fall allows more time for grasshoppers to feed and lay eggs while cool and wet weather increases egg mortality and reduces the activity of grasshoppers at all stages.

Cultivation - tillage eliminates the green plants on which grasshoppers feed that controls and reduce the grasshopper populations.