The world’s largest reserve for migrating Monarch butterflies, located in the Mexican highlands, is suffering from an infestation of bark beetles similar to outbreaks that have killed millions of acres of evergreens in the U.S. and Canada. In an effort to stem the spread of the infestation, Mexican officials
have cut down 9,000 fir trees and buried them or shipped them out of the reserve. So far, the infestation has affected only a small portion of the 33,000-acre core mountaintop wintering grounds, but the outbreaks are occurring in widespread patches, which could indicate a spread of the disease. Mexican officials say the beetles have always existed in the reserve, but that a recent drought has weakened the fir trees and made them more susceptible to the tiny pests, which destroy the bark and kill the firs. Similar bark beetle outbreaks in the U.S. and Canada have primarily been attributed to warmer temperatures, which do not kill off the beetles in winter. The fir trees in the monarch reserve, located 60 miles northwest of Mexico City, provide shelter to the butterflies in cool weather on their southerly migration.