The rubbing of back legs in nature happens when you have high dense populations - overcrowding due to rushing for limited food in an area. Which evolving wings and flying elsewhere would be nature at play.
Real trick would be to curtail grasshopper numbers before they swarm and perhaps a more balanced approach to grasshoppers natural enemies and encouraging habits for those will do well. Chemicals for me are a desperate solution to a problem that got overlooked. Much the same way that ant do wonders with many pests for plants, yet production methods end up curtailing environments that see them thrive in area's that would benefit. So we end up with chemicals for things like aphids when ants will eat them all up for you.