When standing and fallen grand firs, Abies grandis (Douglas ex D. Don) Lindley, were co-attacked by fir engravers, Scolytus ventralis LeConte, and Pityokteines elegans (Swaine), 5.8% of galleries of the latter species were initiated from galleries of the former. Larval S. ventralis avoided contact with both con- and heterospecific galleries, whereas P. elegans adult and larval galleries freely crossed those of S. ventralis. There were strong and weak negative relationships for gallery establishment and emergence, respectively, between the 2 species, but numerous instances in which both species co-inhabited the same resource. Unlike many scolytids, the 2 species did not partition the host according to the diameter of the bole. The results indicate a moderate level of competitive interaction between the 2 species in which P. elegans would either colonize an area of bark before S. ventralis, 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. Inglés

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