Abstract
Dutch elm disease (DED) is a destructive vascular wilt disease of elm (
Ulmus) trees caused by the introduced Ascomycete fungus
Ophiostoma novo-ulmi. In Europe, this DED pathogen is transmitted by elm bark beetles in the genus
Scolytus. These insects carry phoretic mites to new, suitable habitats. The aim of this study was to record and quantify conidia and ascospores of
O. novo-ulmi on phoretic mites of the three elm bark beetle species
Scolytus multistriatus, Scolytus pygmaeus, and
Scolytus scolytus. Spores of
O. novo-ulmi were found on four of the ten mite species phoretic on
Scolytus spp. These included
Elattoma jraxini, Proctolaelaps scolyti, Pseudotarsonemoides eccoptogasteri, and
Tarsonemus crassus. All four species had spores attached externally to their body surfaces. However,
T. crassus carried most spores within its sporothecae, two paired pocket-like structures adapted for fungal transmission. Individuals of
Pr. scolyti also had
O. novo-ulmi conidia and ascospores frequently in their digestive system, where they may remain viable. While
E. fraxilli and
P. eccoptogasteri rarely had spores attached to their bodies, large portions of
Pr. scolyti and
T. crassus carried significant numbers of conidia and/or ascospores of
O. novo-ulmi, P. scolyti and
T. crassus, which likely are fungivores, may thus contribute to the transmission of
O. novo-ulmi, by increasing the spore loads of individual
Scolytus beetles during their maturation feeding on twigs of healthy elm trees, enhancing the chance for successful infection with the pathogen. Only
S. scolytus, which is the most efficient vector of
O. novo-ulmi in Europe, carried high numbers of
P. scolyti and
T. crassus, in contrast to
S. multistriatus and
S. pygmaeus, which are known as less efficient vectors. The high efficiency of
S. scolytus in spreading Dutch elm disease may be partly due to its association with these two mites and the hyperphoretic spores of
O. novo-ulmi they carry.
Keywords
Ulmus,
Ophiostoma novo-ulmi,
Scolytus spp.,
Scolytinae,
Proctolaelaps scolyti,
Tarsonemus crassus,
Phoresy
Citation
Moser, J.; Konrad, H.;Blomquist, S.;Kirists, T. 2010. Do mites phoretic on elm bark beetles contribute to the transmission of Dutch elm disease? Naturwissenschaften 97:219-227.