DED CYCLE

Ophiostoma ulmi s.l., the fungus that causes Dutch elm disease (DED) may either infect elm trees by moving internally through root graft connections or externally by spores attached to a vector. Although many insects and mites that are associated with elm trees may carry spores of O. ulmi s.l. the feeding and reproduction behavior of most of them does not provide substantial opportunity for transmissing the fungus {[393],[768]}. In 1934 transmission of the pathogen by bark boring beetles was demonstrated by Fransen et al. {[313]} and Middleton et al. {[314]}. Elm bark beetles are the only proven vectors that systematically inflict or visit fresh wounds in the sapwood of healthy elms, thereby enabling spore deposition in a place favourable for DED infection. In addition to bark beetles, other beetles like Eutetrapha tridentata Oliv. (common elm borer), the North American ambrosia beetles Xylosandrus germanus Bland., Xyloterinus politus Say, and Monarthrum mali Fitch, the carpenter worm Zuezera pyrina L., and weevils of the genus Magdalis have been suggested as (occasional) vectors of DED {[345],[390],[391],[392]}.