There is one easy way to defeat all of the stage bosses.

1) On the first boss all you need is a pod. Wait until he moves his tail, then shoot your pod into the middle to hit him. Repeat until he is dead.

2) For the second boss you'll also need a pod. When you come into the boss screen, try to fire your pod next to the opening at the top without overshooting. Go to the bottom lefthand side, get low to the ground and as close as you can to the plant. Now call your pod back to you and it should be stuck in the bosses hole. Stay where you are and the boss should never touch you. It will look like your not hurting him, but give it a chance and he will eventually die.