Interactions between Scolytus ventralis and Pityokteines elegans (Coleoptera : Scolytidae) in Abies grandis

When standing and fallen grand firs, Abies grandis (Douglas ex D. Don) Lind ley, were co-attacked by fir engravers, Scolytus ventralis LeConte, and Pit yokteines elegans (Swaine), 5.8% of galleries of the latter species were in itialed from galleries of the former. Larval S. ventralis avoided contact w ith both con- and heterospecific galleries, whereas P. elegans adult and la rval galleries freely crossed those of S. ventralis. There were strong and weak negative relationships for gallery establishment and emergence, respec tively, between the 2 species, but numerous instances in which both species cc-inhabited the same resource. Unlike many scolytids, the 2 species did n ot partition the host according to the diameter of the bole. The results in dicate a moderate level of competitive interaction between the 2 species in which P. elegans would either colonize all area of bark before S. ventrali s, which would then not initiate attack, or in which both species would co- attack a host, but S. ventralis would avoid phloem colonized by P. elegans.