The population of which organisms would most likely increase if there were fewer grasshoppers?

In a given food web, changes in the population of one species affects the population of others, especially the one that serves as the food or the competitor. In the case of grasshoppers, the main food source is grass, vegetables and cereals (basically any plant). If the population of grasshoppers decrease, the population of their main food source, grass and other plants, will increase.

Grasshoppers compete with other herbivores, such as Mormon crickets, etc. It...

In a given food web, changes in the population of one species affects the population of others, especially the one that serves as the food or the competitor. In the case of grasshoppers, the main food source is grass, vegetables and cereals (basically any plant). If the population of grasshoppers decrease, the population of their main food source, grass and other plants, will increase.

Grasshoppers compete with other herbivores, such as Mormon crickets, etc. It has also been reported in studies that grasshoppers compete with larger grazing animals such as bison, for food. Hence, a decrease in population of grasshoppers will mean more food for its competitors. grazing (mammalian) animals and grazing insects. This will result in a higher population of these animals and insects. 

Grasshopper population is controlled by chemical means with insecticides such as malathion and carbaryl, which are commonly used to control the infestation.

Hope this helps.