What is the ruling of Islamic law regarding catching insects and keeping them captive until they die, in order to preserve and display them for ornamentation, after this practice was originally for purposes of study and dissection?

It is permissible to hunt insects and preserve them for educational purposes, due to the scientific benefit therein. This should be limited to the extent of need. However, killing them for adornment is not permissible. If killing for educational purposes is permissible, then they must be killed in a way that hastens their death to spare them from torment, unless the educational purpose cannot be achieved except by killing them in that specific manner.