Mycangial Fungi of Dendroctonus frontalis (Coleoptera: Scolytidae) and thier Relationship to Beetle Population Trends

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Abstract
Females from eight endemic populations of the southern pine beetle, Dendroctonus frontalis Zimmerman, were examined to Determine which of two fungi were present in the mycangium. The fungi Ceratocystis minor (Hedgcock) Hunt var. barrasii Taylor and an unidentified basidiomycete were found together in 10 to 20% of the beetles. Less than 10% of each population had neither fungus in the mycangium, whereas 13 to 47% had C. minor var. barrasii alone. The basidiomycete was the most prevalent fungus in most populations and occurred alone in 38 to 75% of the beetles. Frequency of occurrence of the fungi varied significantly among the eight populations studied. The mean mass of individual females varied significantly (P < 0.01), depending on which fungus was present in the mycangium. Weights varied as follows: females with only the basidiomycete > those with both fungi > those with only C. minor var. barrasii > those with neither fungus. Brood increase ratio and brood survival were significantly related to the frequency of occurrence of the mycangial fungi. The strongest relationship was found between these indices of population trends and the frequency of occurrence of the basidiomycete. Both indices were negatively correlated with the percentage of C. minor var. barrasii in a population.