Two mycangial fungi,Ceratocystis nigracarpaDavidson and an unidentified basidiomycete, were isolated from the walls of pupal chambers made byDendroctollus brevicomisLeConte, along with another fungus,Ceratocystis minorHedge, which is closely associated with the beetle but not found in thc mycangium. Beetles eclosing to the adult stage under axenic conditions had empty mycangia, whereas those eclosing within the pupal chambers acquired spores of both mycangial fungi. Beetles emerging from standing trees had only spores in their mycangia. However, beetles responding to pheromone-baited trees had mycangia filled with spores and mycalia, as did ovipositing females removed from under the bark of newly colonized ponderosa pine. Thus, there is an 8- to 10-day delay between the time beetles emerge and the time the fungi grow and completely fill the mycangium. Beetles apparently do not colonize trees during this time, which suggests that there is a lag between emergence of new adult females and responsiveness to pheromone.