Dear Homeowner,
Master Gardener volunteers are working at Centre County Extension to identify  insect on you river birch. The two most common insect pest for this species is bronze birch borer and birch leaf miner, but your picture does not look like either of those.

I invite you to bring the specimen into our Extension Office and answer some more questions about the health of your river birch. Or email us at <personal data hidden> or call<personal data hidden>
 
I have a link to a government website that give a good overview of birch trees and how to care for them. http://www.na.fs.fed.us/spfo/pubs/howtos/ht_birch/ht_birch.htm

We hope to hear from you soon.
Sincerely,
Ruth Merritt, Master Gardener volunteer, Centre County Extension Hotline team