Insect Vector Behavior and the Evolution of Dutch Elm Disease

Abstract

Several species of bark beetles (family Scolytida) are considered vectors of Dutch elm disease. However, although there is intimate contact between the pathogen and bark beetle during the saprotrophic phase of the disease in the bark of recently killed elms, the breeding and host seeking behavior of the beetles can often reduce their potential to act as effective vectors. This is exemplified by Scolytus multistriatus, the main vector species in North America and also found across Europe, and in New Zealand and Australia. S. multistriatus is frequently ineffective as a vector because of the small number of spores carried by individual beetles. This feature may assist in the control of the disease in North America but it may also be offset by the greater susceptibility of American elms to Ophiostoma novo-ulmi, compared with European and Asiatic elms. The interaction between vector efficiency and host susceptibility will have contributed significantly to the evolution of this highly damaging disease.