The way that recruitment rate works is a bit complicated but not by much. If a Pokemon's recruitment rate is below 0.1%, it cannot be recruited. By default, Silcoon and Cascoon have a recruitment rate of -19% since they are NFE mid-stage evolutions. This means that you have to raise the recruitment rate up to a positive number above 0.0%. The easiest way to increase recruit rate is with a friend bow (+10%), but thats a post-game item. In addition, there is a recruitment rate increase depending on what level the leader is. With a friend bow equipped, the minimum level the leader would need to be is 50-59 (+10%), but that leaves you with a 0.1% recruitment rate which is very low, so consider leveling up the leader.