Attraction of ambrosia and bark beetles to coast live oaks infected by Phytophthora ramorum

Abstract

1 Sudden oak death is caused by the apparently introduced oomycete, Phytophthora ramorum. We investigated the role of bark and ambrosia beetles in disease progression in coast live oaks Quercus agrifolia . 2 In two Marin County, California sites, 80 trees were inoculated in July 2002 with P. ramorum and 40 were wounded without inoculation. Half of the trees in each group were sprayed with the insecticide permethrin [cyclopropanecarboxylic acid, 3-(2,2-dichloroethenyl)-2,2-dimethyl-(3-phenoxyphenyl) methyl ester] to prevent ambrosia and bark beetle attacks, and then were sprayed twice per year thereafter. After each treatment, sticky traps were placed on only the permethrintreated trees. Beetles were collected periodically in 2003. 3 Inoculated trees accounted for 95% of all beetles trapped. The ambrosia beetlesMonarthrum scutellare and Xyleborinus saxeseni and the western oak bark beetle Pseudopityophthorus pubipennis were the most abundant of the seven species trapped. 4 Permethrin treatment delayed initiation of beetle attacks and significantly reduced the mean number of attacks per tree. Beetles did not attack any wounded or noncankered inoculated trees. 5 Trees with larger cankers trapped more beetles early in the disease. Once permethrin lost effectiveness, the number of beetle entrance tunnels was a more reliable predictor of subsequent trap catch than was canker size. 6 Beetles were initially attracted to P. ramorum cankers in response to kairomones generated in the host-pathogen interaction. After beetles attacked the permethrintreated trees, aggregation pheromones most probably were the principal factor in beetle colonization behaviour.bark and ambrosia species accelerates tree mortality by introducing fungi deep into the sapwood, directly (by vectoring) and/or indirectly (by creating tunnels).

Relationship between field resistance to Phytophthora ramorum and constitutive phenolic chemistry of coast live oak

“…growth of callus tissue and canker healing). Mock inoculations did not produce any detectible lesions or SOD symptoms (McPherson et al 2008). Therefore, we are confident that the apparent resistance seen in some Nike trees is not simply the result of inoculation failure.…”

“…The Nike site was subjected to artificial inoculation trials in 2002 and has been under close observation since (McPherson et al 2008). The China Camp (CC) population, which has been observed repeatedly since 2000, is located in Marin County, California, in a natural infection centre and represents remnant trees in an area with extensive mortality (representative coordinates: 38°00¢6¢¢N, 122°29¢13¢¢W).…”

“…The second population (Nike) (representative coordinates: 37°59¢45.1¢¢N, 122°30¢2.2¢¢W) is also located in Marin County, California, within stands with elevated infection levels and is contiguous with the same forested watershed as the CC population. The Nike site was subjected to artificial inoculation trials in 2002 and has been under close observation since (McPherson et al 2008). Briefly, trees had been inoculated by removing a 2cm diameter bark plug from trunks with a hole cutter approximately 1.5 m from the soil line and inserting a 5.5 mm agar plug of P. ramorum isolate Pr52 (originally collected by D. Rizzo, grown on 10% V8 agar for 3 weeks) against the cambium.…”

“…Isolate Pr52 has been used repeatedly by us and D. Rizzo and has maintained its aggressiveness in the course of several years. Bark plugs were replaced, and wounds were covered with aluminium foil and held in place with tape to minimize desiccation and contamination (Rizzo et al 2002;McPherson et al 2008).…”

Effects of Inoculum Density and Wounding on Stem Infection of Three Eastern US Forest Species by Phytophthora ramorum

“…Trees that have sustained some type of injury, such as weather related, animal or insect damage, would be more likely to become infected by P. ramorum. The relationship between certain types of beetles and P. ramorum infection in California forests has been explored (McPherson et al 2008), and the role of insects in forest ecology may be an important factor in terms of numbers of trees that will become infected by P. ramorum. In addition, our results suggest that homeowners who have susceptible species on their property should treat observable injuries with creosote or other means to prevent entry by P. ramorum.…”