Sudden oak death, SOD, is the name given to a new disease that has killed thousands of true oaks and tanoaks in coastal California since 1995. The causal agent is a previously unknown and apparently introduced pathogen, Phytophthora ramorum. A distinctive feature of SOD in coast live oak, Quercus agrifolia, is the presence of bleeding cankers on the main stem. Up to three species of scolytid beetles, Monarthrum scutellare, M. dentigerum, and Pseudopityphthorus pubipennis, selectively colonize these bleeding cankers on living trees. The role of these beetles in SOD etiology has been controversial, since they are generally understood to be saprotrophs and the progression of the disease has not been observed in the absence of insects. In disease progression plots established in early 2000, beetles colonized every bleeding tree that subsequently died within 2 years (n=49), 43% of which snapped off. Breakage consistently occurred where beetle tunneling was most dense. To explore the interactions of beetles with P. ramorum, in July 2002 we randomly assigned 160 mature coast live oaks to 3 groups; inoculated, mock-inoculated, and control. Permethrin insecticide was applied twice yearly to half of the inoculated and mock-inoculated trees to prevent beetle colonization. Beetle arrival was monitored using sticky traps in 2003 on insecticide-treated trees only. Significantly more beetles were trapped on inoculated, bleeding trees than on those that were mock-inoculated. We will discuss the role of these native insects in the etiology of this new disease.
Species 1: Coleoptera Scolytidae Monarthrum scutellare
Species 2: Coleoptera Scolytidae Monarthrum dentigerum
Species 3: Coleoptera Scolytidae Pseudopityophthorus pubipennis (Western oak bark beetle)
Keywords: Sudden oak death, Coast live oak
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