As the old adage goes, "If it ain't broke don't fix it". The ladybugs will do fine for a while. There are many natural ways to go about prevention.
Neem oil is fairly common for prevention and control. Here in Colorado we have literally swarms of grasshoppers that will eat your crops in a day. So some sort of preventative measures are always taken. I've been having good luck spraying Ortho Home Defense around the perimeter of my outdoor grows to keep the grasshoppers at bay. Won't harm your plants from over-spray, either.