Predators of bark beetles locate prey by orienting to their aggregation pheromones, but host location by parasitoids is poorly understood. Bark beetles have intimate relationships with a variety of microbial symbionts which they introduce into trees. Some hymentopteran parasitoids of other herbivores are known to exploit microbial metabolites in host finding. Our objective was to determine if parasitoids are attracted to microbial symbionts vectored by bark beetles. Field studies were conducted in Montana in two phases. Treatments were: 1) Ponderosa pine logs colonized by I.pini; 2) Uncolonized pine; 3) Blank controls. Fungal establishment was determined by weekly isolations from developing I.pini in corresponding treatments. Parasitoids were most abundant during the pine engraver’s first generation, and most were captured during its second and third larval instars. Three species of fungi were consistently associated with I.pini: Opiostoma ips and two yeasts. Several parasitoids were identified, of which three pteromalid wasps were predominant.. Rhopalicus pulchripennis and Heydenia unica showed greater attraction to pines colonized by I.pini than to other treatments. Dibrachys cavus was attracted to host plants, but did not distinguish between colonized and uncolonized pines. We then investigated attraction of parasitoids to the three isolated fungi by adding them to the original design. The predominant parasitoid, H. unica, was equally attracted to pines inoculated with O. ips and pines colonized by I. pini, and more than to pines alone. These results support the hypothesis that some parasitoids use microbial symbionts of bark beetles to locate hosts.