THE ROLE OF FUNGI VECTORED BY DENDROCTONUS-BREVICOMIS LECONTE (COLEOPTERA, SCOLYTIDAE) IN OCCLUSION OF PONDEROSA PINE XYLEM

Following attack by Dendroctonus brevicomis LeConte, ponderosa pines w ere periodically sampled over 7 weeks. Xylem water conduction was asse ssed using a dye flow technique. Fungal isolations were made from func tioning and occluded xylem. Neither Ophiostoma nigrocarpum (Davids.) d e Hoog or other bluestain fungi were commonly found at the interface o f the occluded and functioning xylem. Instead, bluestain fungi appear to colonize already occluded xylem, not cause xylem occlusion by direc t hyphal penetration of functioning sapwood. No evidence for a mutuali stic association of D. brevicomis and its vectored bluestain fungi was found.