Kirk, this will be a long response. I am not certain if all 50 states have sawflies. Some sawflies have been imported and have overtaken from the east coast along the northern & central states to the Pacific. Many sawfly adults are not often observed. A tree being defoliated by the worm/caterpillar larvae may be found by a forester/arborist. Simply put many people do not notice tree health impacts up close, until the tree is dead or in serious decline.
Taken from USDA Report 1998 – more recent surveys encompass Illinois counties.
Scarlet oak sawfly, Caliroa quercuscoccineae Region 9/Northeastern Area: Ohio, West Virginia
Hosts: Black oak, pin oak, red oak, scarlet oak, white oak
The scarlet oak sawfly infestation contined for the second year in southeast Ohio and southwest West Virginia. An area encompassing 217,635 acres was defoliated on the Wayne National Forest in Ohio, and an addtional 76,791 acres was defoliated on adjacent and surrounding private lands. In West Virginia, 185,638 acres was defoliated in Mason, Cabell, Putnam, and Wayne Counties. This area also experienced heavy locust leafminer damage.
Another site showing geographical saturation by the Scarlet Oak Sawfly. http://forestry.about.com/library/silvics/blsilquepal.htmEuropean Sawfly site for Illinois http://urbanext.illinois.edu/bugreview/europeanpinesawfly.html USDA Pest Alert:http://na.fs.fed.us/spfo/pubs/pest_al/sawfly/sawfly.htm