Place a 1x1 wooden foundation, place two walls high on all side but leave one side open. Place 2 pillars where you left it open and lead a ramp on the opposite side for it to walk up and into the box, you can easily slip past the pillars and get out the box trapping the mantis, let it de-aggro by flying out the area for 20-30 seconds and replace the pillars with a wooden wall and fully box it in, place a ceeling on top now you can feed the mantis through the wall without bug repellent.
Best method I was told. Build a 2x2 stone [or wood if low] foundation with 2 high walls, drop in with flyer, feed through wall. Has a massive hitbox to feed it through if lured close to a wall. No repel needed with this method.