Mountain pine beetle (Dendroctonus ponderosae Hopkins) (MPB), can cause extensive ponderosa pine (Pinus ponderosa Dougl. ex Laws.) mortality in the Black Hills of South Dakota and Wyoming, USA. Lower tree densities have been associated with reduced MPB-caused tree mortality, but few studies have reported on large-scale thinning and most data come from small plots that may not be representative of a large area. We quantified MPB-caused tree mortality in 21 pairs of commercially thinned and unthinned stands across the Black Hills. Both pre-and postoutbreak, unthinned stands had higher ponderosa pine basal area, tree density, and stand density index. Quadratic mean diameter was larger in thinned stands, both pre-and postoutbreak. Percent ponderosa pine basal area and tree density killed by MPB in unthinned stands were 38.2 Ϯ 7.0 and 34.4 Ϯ 6.9% compared with 3.9 Ϯ 3.2 and 3.6 Ϯ 2.9% in thinned stands, respectively. All stands were thinned within 2 years of exposure to MPB, suggesting a rapid effect from thinning treatments in mitigating tree mortality attributed to MPB. Stand density reductions through silviculture across a large geographical area can abate MPB-caused tree mortality.

Sap beetles (Nitidulidae) are considered important overland vectors of the oak wilt pathogen, Ceratocystis fagacearum, in the north central United States. Colopterus truncatus and Carpophilus sayi are thought to be the principal sap beetle vectors in Minnesota. Field studies using windoriented funnel traps baited with aggregation pheromones of the insects were conducted during 2 years in east central Minnesota. The studies compared temporal flight dynamics of Colopterus truncatus and Carpophilus sayi from April through October, measured the proportion of dispersing adults of each species carrying viable pathogen propagules, and estimated the populations of contaminated dispersing beetles in oak (Quercus spp.) stands with and without oak wilt. Abundance of Colopterus truncatus peaked in either April or May, but the pathogen was most frequently isolated (20 to 45%) from beetles obtained from oak wilt sites from July through September. However, the highest contaminated insect population (CIP) generally occurred during April and May. Abundance of Carpophilus sayi peaked in October of both years, but the pathogen was most commonly isolated from beetles collected during May and June. The CIP was highest in June. The infective insect potential, as indexed by CIP, was greatest for both species in the spring and was greater for Colopterus truncatus than for Carpophilus sayi.

1 Carpophilus sayi, a nitidulid beetle vector of the oak wilt fungus, Ceratocystis fagacearum, was shown to have a male-produced aggregation pheromone. 2 Six male-specific chemicals were identified from collections of volatiles. The two major compounds were (2E,4E,6E,8E)-3,5-dimethyl-7-ethyl-2,4,6,8-undecatetraene and (2E,4E,6E,8E)-3,5,7-trimethyl-2,4,6,8-undecatetraene, in a ratio of 100 : 18. These compounds, in a similar ratio, were previously reported to be the pheromone of Carpophilus lugubris, a closely related species.The four minor C. sayi compounds (less than 4% as abundant as the first) were also alkyl-branched hydrocarbons and consisted of two additional tetraenes and two trienes. 3 The pheromone of C. lugubris was re-examined to refine the comparison with C. sayi, and C. lugubris was found to have the same additional, minor tetraenes as C. sayi, but not the trienes. 4 A synthetic mixture of the two major compounds was behaviourally active for both sexes of C. sayi in oak woodlands in Minnesota. The pheromone was tested in combination with fermenting whole wheat bread dough (a potent synergist of nitidulid pheromones). The combination of the 500-mg pheromone dose and dough attracted at least 30-fold more C. sayi than either pheromone or dough by itself. The synergized pheromone has potential as a tool for monitoring insect vector activity in an integrated management program for oak wilt. 5 Although C. lugubris was not present at the Minnesota test sites, two other Carpophilus species, Carpophilus brachypterus and Carpophilus corticinus, were clearly cross-attracted to the synergized pheromone of C. sayi.

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