2001 Blodgett Forest Research Symposium

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ABSTRACT 24 Effects of Artificial Inoculation of Heterobasidion annosum on Landing Rates of Bark Beetles (Coleoptera: Scolytidae) on Ponderosa Pine Andrew J. Storer, Pierluigi Bonello, William R. McNee, Thomas R. Gordon, and David L. Wood

A considerable body of evidence points to predisposition of root-diseased conifers to colonization by tree-killing bark beetles. To determine whether root diseased trees are more attractive to bark beetles, landing rates were monitored on trees inoculated with the root and butt rot fungus, Heterobasidion annosum, and compared with landing rates on mock inoculated and uninoculated control trees. In 1997, thirty trees were inoculated at the root collar, thirty mock-inoculated and thirty used as controls in each of two adjacent, stands of 35 year old ponderosa pine (referred to as east and west plots) at the University of California’s Blodgett Forest Research Station (BFRS), Georgetown, El Dorado County, California. Four equally-spaced wooden dowels colonized by H. annosum were inserted at the base of inoculated trees, and four un-colonized, sterilized dowels were inserted at the base of mock inoculated trees. Each of the 180 trees was fitted with four, 0.22 m2 sticky traps made of 3 mm hardware cloth coated with Tanglefoot and sprayed to runoff with the insecticide carbaryl (Sevin, Ortho). Two of the four traps were tied to the trunk 4-5 m above ground, while the other two were tied at the base. All scoytids were removed from the traps in July and November, 1997, and again in July and November 1998, and in November 1999 (the traps were re-coated with Tanglefoot and re-sprayed with carbaryl in May 1998 and May 1999). Differences between the treatments and plots were tested for each species of bark beetle using ANOVA. Trees under attack were eliminated from the analysis as pheromone induced-landings would confound treatment effects. Independently of plot, treatment and year, the mean number of beetles/trap/date in decreasing order of frequency were: Hylastes spp. (0.702), Gnathotrichus spp. (0.340), Ips latidens (0.161), Dendroctonus brevicomis (0.156), I. paraconfusus (0.136), and D. ponderosae (0.043). Differences among treatments were non-significant (a = 0.05), with the exception of I. latidens in the first period of 1998. Overall, the east plot was characterized by higher trapping rates than the west plot (0.308 vs. 0.204, respectively), but the differences between plots were non-significant. However, catches for individual genera/species at each date often differed by plot. Representative data for western pine beetle and the California 5-spined ips are shown in Table 1. Thus, under the conditions of our experiment, bark beetles appear to land on their hosts at random, irrespective of inoculation status. This study will be expanded to correlate bark beetle landing rates with local population sizes and incidence of bark beetle associated tree mortality. In addition, the landing rates of bark beetles on other tree species will be monitored to determine whether landing is host specific in mixed stands of trees. Table 1. Mean number of beetles/trap/date for Ips paraconfusus and Dendroctonus brevicomis. Date refers to the dates that insects were removed from the traps. Date West Plot East Plot Inoculated Mock-inoculated Control Ips paraconfusus California 5-pined ips July 1997 Nov 1997 July 1998 Nov 1998 Nov 1999 0.008a 0.155a 0.019a 0.003a 0.008a 0.886b 0.172a 0.028a 0.008a 0.069b 0.358 0.117 0.017 0.004 0.038 0.508 0.200 0.042 0.008 0.060 0.475 0.175 0.012 0.004 0.017 Dendroctonus brevicomis Western pine beetle July 1997 Nov 1997 July 1998 Nov 1998 Nov 1999 0.000a 0.219a 0.585a 0.044a 0.197a 0.125b 0.111b 0.087b 0.036a 0.158a 0.033 0.142 0.371 0.047 0.169 0.079 0.167 0.250 0.038 0.207 0.075 0.188 0.387 0.038 0.157 Values for the same species on the same date in different plots followed by different lower case letters differ significantly (P<0.05; ANOVA of square root transformed data). Differences among treatments were non-significant. Key to dates: 1997-1 = July 1997, 1997-2 = November 1997, 1998-1 = July, 1998- 2 = November 1998, 1999 = November 1999. Left: Pre-commercial thinning by chainsaw Blodgett file photo VEGETATION CONTROL: Vegetation control around growing trees offers optimum growing conditions, eliminating competition for sunlight, water and soil nutrients. Hand mechanical clearing of brush and small volunteer trees is done regularly by chainsaw and brush cutters. Larger clearing is done by slash machinery or earth moving equipment. Hand grubbing, weeding by hand and hoe, is also done occasionally. Some herbicides are used, sprayed directly on the leaves of the plants to be eliminated, once or twice during the lifetime of the stand. Only benign poisons are used, those less lethal than the average agricultural herbicides. Left: Herbicide application Blodgett file photo Left: A masticator efficiently pre-commercial thins an average of 3-4 acres per day. Photo by Gunnar Schade

Contact Author: Andrew J. Storer, Division of Insect Biology, 201 Wellman Hall, University of California, Berkeley, Berkeley, CA 94720, (510) 642-5806, e-mail: storer@nature.berkeley.edu Pierluigi Bonello and Thomas R. Gordon Department of Plant Pathology, University of California, Davis, CA95616 Pierluigi Bonello Current address: Dept. of Plant Pathology, The Ohio State University, 201 Kottman Hall, 2021 Coffey Road, Columbus, OH 43210 David L. Wood Division of Insect Biology, University of California, Berkeley

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