What stage of orchid do you have or are you refering to? Small L1 orchid or any flower type mantis needs food almost every other day. But adult orchid can go without for a long time like 10-20 days. I have an adult male orchid i haven't fed for a week and he is doing fine. and that also depends on what temperature are you refering to. The warmer the temp, the better appetite mantis will get. Room temperature of 70F is on the cold side for a tropical species like Orchid mantis. They need a good temp of 85F/70% humidity with daily misting if possible to avoid mismolting problem.