Mortality of birch leafmining sawflies (Hymenoptera: Tenthredinidae):: Impacts of natural enemies on introduced pests

Larvae of introduced birch leafmining sawflies in Alberta, Canada suffered light mortality from native generalist parasitoids of the family Eulophidae (Hymenoptera: Chalcidoidea). Eggs of Profenusa thomsoni (Konow) were attacked by 2 native species of Trichogramma (Chalcidoidea: Trichogrammatidae), and larvae of P. thomsoni were attacked by a more specialized native koinobiont parasitoid, Lathrolestes luteolator (Gravenhorst) (Ichneumonidae: Ctenopelmatinae). Spiders, beetles, hemipterans, thrips, ants, neuropterans, and flies preyed on Fenusa pusilla (Lepeletier) and P, thomsoni. Mortality levels differed between F, pusilla and P. thomsoni and tended to be higher in earlier instars, on urban trees, and during 1993. Experiments during 1993 revealed little predation of larval F. pusilla when population densities were uniformly high, but during the 1994 experiments, predators efficiently exploited branches having high densities of immature P. thomsoni within a matrix of low background P. thomsoni density.