(Portland, OR) -- The emerald ash borer is one of the most destructive invasive species in the country. It's killed more than 100 million trees since it was found in Michigan in 2002. Portland Parks has a response plan. The bug has been found in outlying communities, but not yet in Portland. The city has 95-thousand ash trees. The Parks Department is treating healthy ash trees in City parks with insecticide to prevent infestations. They're also allowing residents to replace ash trees under six inches in diameter with free permits for other species of trees.