The Distribution of the European Spruce Sawfly, Diprion polytomum (Htg.) in the Scandinavian and Eastern Baltic Countries

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Since 1930 the European spruce sawfly (Diprion polytomum) has caused severe damage in eastern Canada and is a meance to the spruce woodlands in the northeastern part of the United States. In 1938 under a cooperative arrangement with the Division of Entomology, Canadian Department of Agriculture, and the Farnham House Laboratory, Imperial Institute of Entomology, England, which were to continue their collecting in the central European area for the recovery of natural enemies, the Bureau of Entomology and Plant Quarantine, United States Department of Agriculture, made a survey of the Scandinavian and eastern Baltic countries to extend the knowledge of the distribution of the sawfly ; to discover, if possible, better or equally as good collecting grounds, where new species of parasites might be found ; and to obtain additional information regarding the better known species of parasites. The most favourable habitats of the sawfly are found in the one-generation areas under conditions which provided a maximum of sun-heat, moisture, and shelter, near to the upper limits of spruce growth. The least favourable habitats are the drier, less humid places, especially in the two-generation areas. The sawfly was found everywhere on spruce, from the German-Danish border in Denmark and in southern Norway to the northernmost spruce forests of Sweden, and from far above the Arctic Circle in Finland southward through the eastern Baltic countries of Estonia, Latvia and Lithuania. The range of distribution covered in this survey was from approximately latitude 55° in Denmark and Lithuania to latitude 68° 45′ in Finland. This includes most of the Scandinavian Peninsula, Fennoskandia, and the eastern Baltic countries. Spruce comprised from 25 to 40 per cent. of the productive forest land of this large area. Large collections of the European spruce sawfly were made in Sweden and Finland for the Canadian Division of Entomology.