Intraspecific competition in Tomicus piniperda (L.) was studied in Ascot, United Kingdom, with special emphasis on its effect on progeny adult (i.e., offspring) weight and progeny production. Although the weight of female progeny adults was significantly decreased by increasing attack density (density of colonization), the latter did not significantly affect weight of male progeny adults. Similarly, increasing adult female weight was significantly related to increasing egg gallery length, number of hatched eggs, and final production of progeny adults. This production was also affected by host (tree) species. Females breeding in Pinus sylvestris (L.) showed a higher production of progeny adults than those in Pinus nigra variety maritima (Ait.) Melville. Overall, increasing intraspecific competition appears to contribute to the regulation of T. piniperda populations through reduction of weight and fecundity of female progeny.