Oak jewel beetle (Agrilus biguttatus). This approximately 1 cm long beetle have a metallic green color. The beetle feeds on pollen and nectar; the larvae, however, live on oak bark and wood.
The larvae prefer diseased and weakened trees. Due to periods of drought in winter and spring + high nitrogen emissions from agriculture, among other things, many oaks are in bad shape.
Excess nitrogen keeps the root system small and shallow, causing rapid damage to the tree during a dry spell. The large amount of nitrogen acidifies the soil and hydrogen ions displace minerals. The minerals then wash away into the subsoil and the tree produces leaves with mainly nitrogen and only a few minerals. Nitrogen-rich leaves are a favored food source of herbivorous insects (e.g., larvae of the winter moths). The now weakened oaks are then visited by the larvae of the Oak jewel beetle with their preference for diseased and weak trees. The larvae dig their harmful tunnels in bark and trunk. The already weakened trees usually do not survive this.
After damage, recovery is no longer possible.
Does not apply.