Evaluating insect-mediated dispersal of Scytalidiumuredinicola for biological control of western gall rust

Abstract

The potential for augmentative biological control of western gall rust, caused by Endocronartiumharknessii (J.P. Moore) Y. Hiratsuka, on lodgepole pine (Pinuscontorta Dougl. var. latifolia Engelm.) was investigated near Hinton, Alberta. We sought to determine whether a mycoparasite, Scytalidiumuredinicola Kuhlman et al., of western gall rust could be enhanced through releases of a beetle, Epuraeaobliquus Hatch, which can serve as a vector for the mycoparasite. Mycoparasites parasitized increasing proportions of the sporulating tissue on older galls, so that most galls 10 years or older had more than 95% of their sporulating surface parasitized. Scytalidiumuredinicola was the most common mycoparasite in the sporulating tissue of western gall rust, was present early in the season, and appeared to overwinter inside the tissue of the gall. Adults and larvae of E. obliquus were important in spreading the mycoparasite across the surface of galls, especially on galls younger than 10 years. From a mark recapture experiment and sticky-trap sampling, it was determined that E. obliquus is strongly attracted to western gall rust and therefore is a promising candidate to disseminate the mycoparasite. In a small-scale release experiment, beetles inoculated with S. uredinicola did not successfully initiate significant numbers of infections. However, of the few infections initiated under experimental conditions, all occurred in the treatment providing beetle access.