Wood-boring insects

Some insects that attack chestnut trees (borer, xylebore, cossus, zeuzere ...) have cortical development stages, which when they occur at the level of the generative base block the vessels by thyllosis which blocks the circulation of the sap.  This results in a blackish ooze of oxidised sap through the bark.

The entrance/exit holes and the presence of sawdust allow a diagnosis in favour of the presence of these insects (Figures 1 and 2).