Untersuchungen über die Aussichten einer biologischen Bekämpfung von Scolytiden an Ulmen als Mittel zur Einschränkung des „Ulmensterbens”

Abstract

AbstractStudies on the possibilities of biological control of elm bark beetles (Scolytidae) with the view of reduction of the dutch elm disease. At the request of the Michigan State University the parasite complex of the European elm bark beetles, S. scolytus and S. multistriatus, was studied in eastern Austria by the European Station, C.I.B.C., in 1969. 10 species of parasites, the Braconids Coeloides scolyticida, Dendrosoter protuberans, Ecphylus silesiacus and Spathius rubidus, and the Chalcids Cheiropachus quadrum, Cerocephala cornigera, Dinotiscus aponius, Entodon ergias, Eurytoma arctica, and Eurytoma morio were found.Between 1970 and 1972 the studies were continued on behalf of the Canadian Forestry Service, and the mortality of the summer generation of S. scolytus and S. multistriatus was studied in two localities in 1970 and 1971. The total mortality between June and September was 76,3 and 79,3% for S. scolytus, and 75,1 and 84,8% for S. multistriatus. The mortality of the eggs (between 16 and 25%) was mainly caused by physical factors, losses through predation remained below 2,5%. The mortality of the first and second instar larvae reached 48% for S. scolytus, and 64% for S. multistriatus. Between 6 and 25% of the mortality of these two instars was caused by predation, the Dolichopodid M. nitida being the most important predator. The mortality of the larval instars L3–5 accounted for 30% of the total mortality. Seven species of ectoparasites were responsible for most of this mortality. C. coeloides was the most important parasite of S. scolytus, and D. protuberans was the dominant parasite of S. multistriatus. Parasitism by the endoparasite E. ergias remained below 5% in the larvae of both species. No mortality was observed for the pupae and the teneral adults. No diseased larvae or pupae were found.