Gypsy moth caterpillars cause widespread defoliation of shade trees and forests, sapping strength from the trees and leading to their early demise. (owlcation.com)
Some tree species, for example larch, are notorious for having incomplete or even (locally) absent rings, most often due to high levels of defoliation by insects. (realclimate.org)
One example of such a product: The North American forest industry is using bacterial biopesticide Bacillus thuringiensis to fight defoliation. (sciencemag.org)