CLAUSTHAL-ZELLERFELD, Germany — Nestled in the spruce trees in the Harz mountains of northern Germany is a bark-eating pest not much bigger than a sesame seed. Known as “book printers” for the lines they eat into the bark that fan out from a single spine resembling words on a page, these eight-toothed beetles have always been part of the local forest.  …Two-thirds of the spruce in the region have already been destroyed, said Alexander Ahrenhold from the Lower Saxony state forestry office, and as human-caused climate change makes the region drier and the trees more favorable homes for the beetles’ larvae, forest conservationists are preparing for the worst. …Experts say there’s no easy solution, but forest managers work to remove trees that might be susceptible to beetles as early as possible and use pesticides where they’re needed.