The association of parasitism by the nematode Deladenus siricidicola with a per tree Sirex density (Logistic regression model coefficient P < 0.026; Table 3a) and b fraction of Sirex in the tree parasitized by rhyssines (Logistic regression model coefficient P < 0.0001; Table 3c). Each point represents a dissected S. noctilio. The points are distributed vertically in order to show the amount of data at each host density. The points below the curves are parasitized D. siricidicola (Yes) and the points above the curve are not (No). See the text for explanation of the statistical models.