In June 1922, Hearst Hall, the women's gymnasium on the Berkeley Campus of the University of California, burned to the ground. The heat therefrom caused the deaths of three fine specimens of Monterey Cypress growing nearby, thus setting the stage for a local episode in the interaction between a wood-wasp of the genus Sirex and a parasitic wasp of the genus Ibalia. This particular host-parasite interaction is a widespread one of very ancient origin. The 1922 episode of this interaction was manifested as soon as the three dead cypress trees lhad attained a condition which was particularly attractive to the females of Sirex and the females of Ibalia. The larvae of Sirex burrow in and feed upon the timber of coniferous trees; the larvae of Ibalia live parasitically within the Sirex larvae and ultimately destroy them.