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Seasonal Dispersal of the Oak Wilt Fungus by Colopterus truncatus and Carpophilus sayi in Minnesota

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.