Association betweenDendroctonus valensand black stain root disease on ponderosa pine in the Sierra Nevada of California

The host-colonization behavior of the red turpentine beetle,Dendroctonus valensLeConte (Coleoptera: Scolytidae), was investigated in stands of ponderosa pine,Pinus ponderosaP. & C. Lawson (Pinaceae), with black stain root disease in the central Sierra Nevada of California. By felling live trees, we found that trees with pitch tubes produced during the initiation of tunneling byD. valenshad a significantly higher incidence of black stain root disease, caused byLeptographium wagenerivar.ponderosum(HarringtonetCobb), than trees without pitch tubes. Trees with the mostD. valenspitch tubes had the greatest likelihood of being diseased. Additionally, observations over a 3-year period revealed that trees withD. valenspitch tubes had a significantly higher mortality rate than trees without pitch tubes. Infection byL. wageneriwas confirmed for most of the trees that died, and death typically did not occur without mass attacks by the western pine beetle,D. brevicomisLeConte, and (or) the mountain pine beetle,D. ponderosaeHopkins. Trees with the mostD. valenspitch tubes had the highest mortality rate. An experiment was conducted to compare the attraction ofD. valensand other insects to wounded-diseased, wounded-symptomless, and unwounded trees. MoreD. valens,Spondylis upiformisMannerheim (Coleoptera: Cerambycidae), andHylastesspp. (Coleoptera: Scolytidae) were attracted to wounded trees than to unwounded trees. Catches of these beetles on wounded-diseased trees were not significantly different from catches on wounded-symptomless trees.