What will kill the redhead sawfly?
The US Forest Service has a good factsheet on the redheaded pine sawfly: http://www.na.fs.fed.us/spfo/pubs/fidls/pine_sawfly/pinesawfly.htm . Chemical controls may be available for large infestations. However, natural biological controls (such as rodents) are generally effective, especially when combined with cultural controls (including planting diversified species and culling weak host trees.) You should contact your county Extension agent for details about what types of controls are recommended in your area.
I hope this information is helpful.