Feeding by Scolytus bark beetles to test for differently susceptible elm varieties

Dutch elm disease (DED), caused by the fungi Ophiostoma ulmi and O.novo-ulmi, has reduced elm populations severely in Europe and North America. Breeding programmes are in action to find less susceptible elm varieties suitable for re-establishing elm stands. Bark beetles, mainly Scolytus spp., are the only known natural vectors of DED. During twig feeding, beetles transfer Ophiostoma spores to healthy elms. Thus, less palatable elms should run a lower risk of DED infections. In feeding preference bioassays, we offered twigs from elms exhibiting different degree of susceptibility to O.novo-ulmi, together with non-host trees to Scolytus beetles. Scolytus multistriatus preferred wych elm, Ulmus glabra, to 100% in two-choice tests, whereas S.laevis did not discriminate between a tolerant and a susceptible variety of field elm, U.minor. We suggest that the feeding assay is useful as a low-tech method in breeding programmes for evaluating the suitability of promising elm genotypes to vector insects.