Remember most of the insects in your yard are beneficial but a few may cause problems. They feed for several weeks on older pine needles, finishing about the time the new needles elongate. When disturbed, the larvae throw their heads back in unison, a behavior that may scare away birds and other predators. Since the larvae do not eat the new needles, their feeding doesn't kill trees and shrubs, but plants look sparse for a year or two until the newer needles cover over the bare areas. Pine sawfly larvae are easy to control, because they feed in large groups only on a few branches.
Hand remove by shaking the infested branch over a pail of soapy water.
Most of the larva will fall in the pail and drown. Hand picking also works. If you choose to use an insecticide, spray only the infested branches. Birch leafminers are also a type of sawfly. Shortly after the birch leaves unfold, the female will lay her eggs in the leaves.