Will starve to death first. Cabbage butterfly uses mustard oil as a host location factor and as a phagostimulant. If you soak filter paper the larvae will eat it. Similarly if you put it on a non-host they will eat that host even if it kills them. If you remove from the normal host they will not eat it.
Grasshoppers are paurometabolous.
They lay their eggs in soil and do not take care of them. Start by searching for the right odor. Choose host by visual characteristics. Time of day and amount of sunlight play a role. Once proper visual stimuli are presented the feeding behavior is released.