Submitted to: Agricultural and Forest Entomology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/10/2004
Publication Date: 5/1/2005
Citation: Moser, J.C., Konrad, H., Kirisits, T., Carta, L.K. 2005. Phoretic mites and nematode associates from scolytus multistriatus and s. pygmaeus (coleoptera: scolytidae) in austria. Agric. and Forest Entomol. 7: 169-177. Interpretive Summary: Elm bark beetles are the principal vectors of the fungi that cause Dutch elm disease, which threatens residential and forest elm trees worldwide. Although mites and microscopically small nematodes (roundworms) have the potential to be used as biocontrol agents, one problem that must be solved first is to determine how they affect the survival and performance of different elm bark beetle species and their ability to spread the disease-causing fungus. In this study of mite and nematode associates of two elm bark beetle species, forest entomologists from Austria and the USDA Forest Service discovered nine mite species, two of which had never been found on these beetles before. An ARS plant pathologist identified one species of nematode in the gut of one beetle species, and another nematode species under the wings of both beetles. This information is significant because this is the first indication that potentially complex interactions of microorganisms occur between the bark beetles, their associated mites and nematodes, and the pathogens responsible for Dutch elm disease. Some of these mite species may feed on one or several fungi, nematodes, other mites and/or beetle eggs. This information will be used by researchers to determine which mites and nematodes are most damaging to the beetles, and whether mites can carry the disease-causing fungus from diseased to healthy elms. Consequently, this information could be useful in biological control programs against elm bark beetles and Dutch elm disease.
Technical Abstract: The species assemblages and abundance of phoretic mites associated with the elm bark beetles, Scolytus multistriatus and Scolytus pygmaeus were studied in Austria. Stem sections from an elm tree infested by the two Scolytus species were collected at one locality in Eastern Austria, and placed in a laboratory rearing cage. Beetles were collected after emergence from the logs and subsequently examined for the occurrence of phoretic mites. A total of 3922 individual mites were recorded from 144 adults of Scolytus multistriatus and 178 adults of S. pygmaeus. The species spectrum was identical and the relative abundance of mites was very similar for both species of scolytids. Nine mite species, including Pyemotes scolyti, Pseudotarsonemoides eccoptogasteri, Trichouropoda bipilis, Tarsonemus crassus, Proctolaelaps eccoptogasteris, Proctolaelaps scolyti, Chelacheles michalskii, nr. Eueremaeus sp., and Elattoma sp. were detected. Two of the nine species, nr. Eueremaeus sp. and Elattoma sp., are documented here as new associates of Scolytus spp. Pyemotes scolyti was the most frequent mite species, and P. eccoptogasteri and T. bipilis were relatively common, whereas the other mites occurred occasionally or were rare. The trophic roles of most of the mites associated with S. multistriatus and S. pygmaeus are poorly known, but they may include fungivores, parasitoids of bark beetle broods, predators of bark beetle broods and/or mites and/or nematodes. Besides phoretic mites, two nematode associates were seen on the investigated insects. The juvenile stages of a species of Tylenchida-Aphelenchina occurred under the elytra of both scolytid species; the adults of a Neoparasitylenchus sp. were present inside abdomens of S. multistriatus, but absent from S. pygmaeus.