Any pest of a tree that is not lethal or disfiguring can be considered minor. Birch trees have a number of minor pests. The least significant is the paper wasp which will peels a strip of bark causing a few twigs to die back. Spittle bugs and aphids do more damage than wasps but are still minor. Both insects are sap feeders and will cause leaf loss.
Spittle bugs protect themselves in a frothy spittle.
Aphids are often found in large numbers under leaves. Sometimes aphids will cause leaf distortions. Of the two aphids more frequently warrant control measures. The insects can be controlled with contact insecticides. Two cultural problems manifest themselves quite are regularly.