LEAF MINERS - The larvae of some flies, moths,sawflies and beetles feed in between upper and lower leaf surfaces; these pests are collectively known as leafminers (example: birch leafminer).  They may cause narrow curved tunnels in the leaves, or large silvery brown blotches.  Severe infestations can cause leaves to brown and drop.  The most effective control is hand-picking and destroying infested leaves.  Chemical controls are usually ineffective because larvae are protected within the leaves for most of their lives.