This 3D scan shows the special pockets where the beetle larva stores its protective bacteria. (Image credit: L.V. Flórez, ... which secrete chemicals that are toxic to fungus. In adult beetles, ...

“The beetle larvae lived—feeding, defecating, ... [Related: These beetles sniff out fungus-infected trees to find their next target.] ...

The beetle and thereby Dutch elm disease are not seen again until the next generation of trees age. Another option is the mutation of fungus and change to or from favorable environmental conditions.