D V Sumerford, Warren G. Abrahamson and A E Weis. "The effects of drought in the Solidago altissima - Eurosta solidaginis - natural enemy complex: population dynamics, local extirpations, and measures of selection intensity of gall size" Oecologia Vol. 122 (2000)
Available at: http://works.bepress.com/warren_abrahamson/53/