Shortly after World War I, a new disease previously unknown among elms emerged in Holland. It spread rapidly from Europe to Great Britain (1927), United States (1930), and Canada (1945), killing millions of elms. The disease known, as Dutch elm disease (DED) is a wilt disease, caused by the fungus Ophiostoma ulmi. It is transmitted from tree to tree by elm bark beetles (scolytid) vectors. Numerous attempts to control the disease have concentrated on the reduction of insect vector populations, exploitation of natural host resistance, extensive application of fungicides and integrated pest management. In spite of these efforts in Canada, the disease continues to migrate westwards threatening the elm populations in Saskatchewan and Alberta. Today there are approximately 700 000 elm shade trees in cities and towns across Canada and their value exceeds $2.5 billion dollars.With the advance of molecular biology new, powerful tools are now available to study, in greater detail, the molecular and biochemical mechanisms of the DED pathogen, with particular reference to the mechanisms that induce host defenses. A glycoprotein has been isolated and identified such that when injected either in liquid or pellet form into the elm tree, significantly reduced the wilting symptoms of both five-year old elm seedlings and 10 cm diameter trees. The elicitor induces a chain of defensive reactions that prevent the rapid spread of the fungus within the vascular system of the host. Key words: Ophiostoma ulmi, elm bark beetle vectors, induced resistance, chemical control, RFLP, mitochondrial DNA, ribosomal DNA, virus-like DNA, resistance breeding

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The hydrophobic protein cerato-ulmin (CU), produced by Ophiostoma ulmi, has been implicated in the pathogenicity of this fungus on elm. Primers were designed based on the nucleotide sequence deduced from the published CU amino-acid sequence, and a DNA fragment of the cu gene was amplified using the polymerase chain reaction. The amplified cu fragment was used as a hybridization probe to identify and isolate the cu gene from a genomic DNA library of an aggressive isolate of O. ulmi ( = O. novo-ulmi). The cu coding region is interrupted by two introns and encodes a 100 amino-acid prepro-CU polypeptide that is processed to a 75 amino-acid mature protein upon secretion. CU shows significant sequence similarity to hydrophobins secreted by certain other fungi.

29Maiszunslers, Ostriniu nubikzlis Hbn., mit der Verwirrungstechnik. Mitt. Schweiz. Ent. Ges. DAUMAL, J.; VOEGELE, J.; BRUNETTI, P., 1975: Les trichograrnmes. 11. Unite de production massive et quotidienne d'un hBte de substitution Ephestia kuehniellu Zell. Ann. Zoo1.-Ecol. Amin., 7, 45-59. MEIER, W.; ANDRESXA, S.; KOLAR, O., 1972: Neuere Beobachtungen zurn Auftreten des Maiszunslers. Mitt. Schweiz. Landw. 20, 151-163. MEISSELI~RE, C. de la, 1982: Methodes d'ivaluation des risques. Agromais, 8, 27-29. MURBACH, R.; HACHLER, M.; GOY, G., 1973: La pyrale de rnds (Ostriniu nubilalis Hbn.) en SUTER, H.; RAMSER, E., 1978: Auftreten und biologische Bekampfung des Maiszunslers (Ostriniu J4, 87-98. Suisse romande. Rev. suisse Agric., 5, 108-111. nubilalis Hbn.) in der deutschsprachigen Schweiz. Mitt. Schweiz. Landw. 26, 57-65. AbstractInundative releases of Trichogrurnmu minuturn Riley for biological control of the spruce budworm, Choristoneuru furniferunu (Clemens), were investigated in Canada's boreal forest during 1982 and 1983. The most significant factors affectin the level of egg mass parasitism were the time of release, the density of the parasitoids, and the focal weather conditions. Food supply to the female parasitoids, vertical location of the host egg mass in the stand, intensity of solar radiation, and density of the host insect were less im ortant. Parasitism was not affected by the tree species on which budworm e g masses were laid: Parasitoids reared at different temperatures and on different host eggs differed in biological characteristics and could influence the success of field releases. Geographical strains of T. minuturn were not considered as important in subsequent releases as the rearing conditions because of the high degree of individual variation within each strain.