What insect has defoliated my fruit trees and how do I manage them?

Question: I need help with fruit tree caterpillar damage. In very short order, my pear tree is completely defoliated, and my plums and apple are seriously set back. The culprits are 3/4″ light green worms. Any idea what they are and what I should do now? Photo used with permission from read more What insect has defoliated my fruit trees and how do I manage them?