Invasive pests are also attracted to the paper birch, though with harmful effects. Two insects are prominent in the destruction of the birch tree- the bronze birch borer and the birch leaf miner. The bronze birch borer enters the tree as larva and grows to eat out tunnels of the cambium of the tree, the part of the tree responsible for producing new cells. The insect will eventually create a girdle around limbs, which cuts off sap flow to the limbs and ultimately kills the tree. The effects of the bronze birch borer can first be seen at the crown of the tree, as a birch dies from the top down. The birch leaf miner, Fenusa pusilla, was introduced into America in 1923 in Connecticut. It lays its eggs on the leaves of the paper birch and eats the leaves until brown and dead. If too many leaves are eaten and killed, the tree as a whole will be weakened for it will not receive stores of nutrients from the leaves. This leads to a slow death of the tree. Combating this pest often relies on the application of dimethoate to the roots of the birch. The chemical will be absorbed and kill the miner.