You can use the neem oil about every 5 days yeah, but you don't want to do it forever. Caterpillers are tough, though, and you might need something stronger like anise, thyme or clove. Extracts of anise and clove both give a pretty quick kill, but like most essential oils, have very short residual periods. With the neem oil though, just be careful not to overapply because it can have long term effects on the plant.