Pumping the web is apparently a defensive action of Argiope aurantia. Here she is both weaving the circumferential web elements and pumping the web. No stimulus of pumping was apparent other then me and my lights :)
For slow motion, after starting the playback, click the gear in the lower right and select speed of 0.5 or 0.25
Here she is 3 weeks ago weaving with no pumping
Argiope aurantia weaving circumferential elements
A. aurantia waiting
A. aurantia weaving
Painting stabilimenta
Painting stabilimenta
Extruding a ribbon of silk
Fine silk ribbon
A tangle of silk
Extruding ribbon
Spinnerets extrusion process
C. Frank Starmer