arcpy - Passing Selection from Combo Box into Definition Query using Python AddIn?

I am trying to pass the users selection into a definition query in an addin combo box python script.

Basically, I have a feature class with a field called "SITE". I build a python list from that field (using the search cursor and appending the results) and pass it into the combo box items list. The user will choose a value in the combo box box from that list. I want to further pass the users selection into a definition query.

You can see in my script below, I just tried to pass the selection into the definition query, but it crashes the whole combo box and toolbar. I've tried converting it to string, placing quotes around it, etc and no luck. Obviously I am doing something wrong with. I believe it's how I'm passing the selection. As suggestions?

import arcpy
import pythonaddins

sitename = []
for row in arcpy.SearchCursor("Z:\Geodatabases\Test.gdb\Tesfc"):
sitename.append(row.SITE)

class ComboBoxClass(object):
    """Implementation for SolsticeFigureUpdater_addin.combobox (ComboBox)"""
    def __init__(self):

        self.items = sorted(sitename)
        self.editable = True
        self.enabled = True
        self.dropdownWidth = 'WWWWWWWWWWWWWW'
        self.width = 'WWWWWWWW'
    def onSelChange(self, selection):
        mxd = arcpy.mapping.MapDocument("CURRENT")

        for df in arcpy.mapping.ListDataFrames(mxd):
            if df.name == "DFMAIN":

                main = arcpy.mapping.ListDataFrames(mxd, "DFMAIN")[0]
            if df.name == "DFINSET":
                dfinset = arcpy.mapping.ListDataFrames(mxd, "DFINSET")[0]

        for lyr in arcpy.mapping.ListLayers(mxd, "", dfmain):
            if lyr.name == "PDA Boundary":
                lyr.definitionQuery = '"SITE" =' selection

        arcpy.RefreshActiveView()
        arcpy.RefreshTOC()



    def onEditChange(self, text):
        pass
    def onFocus(self, focused):
        pass
    def onEnter(self):
        pass
    def refresh(self):
        pass

Answer

I nailed down my issue. I had to wrapt the selection in quotes, but I had to do it using concatenation in the definition query:

lyr.definitionQuery = '"SITE"' + "=" + "'" + selection + "'"

Cheers, Mike