. Cooperative economic insect report. Beneficial insects; Insect pests. - 541 - INSECTS NOT KNOWN TO OCCUR IN THE UNITED STATES LARCH THRIPS (Taeniothrips larlcivorus Kratochvil and Farsky) Economic Importance: This thrips was first recorded as the causal agent of die-back disease of larch in 1941 in Czechoslovakia. A toxin is injected in the process of feeding by the thrips. Extensive areas in central Europe are now affected by this pest. Ten to twenty-year-old stands of European larch grown beyond its natural range have been especially damaged by attacks of this species in large masses, part
. Cooperative economic insect report. Beneficial insects; Insect pests. - 541 - INSECTS NOT KNOWN TO OCCUR IN THE UNITED STATES LARCH THRIPS (Taeniothrips larlcivorus Kratochvil and Farsky) Economic Importance: This thrips was first recorded as the causal agent of die-back disease of larch in 1941 in Czechoslovakia. A toxin is injected in the process of feeding by the thrips. Extensive areas in central Europe are now affected by this pest. Ten to twenty-year-old stands of European larch grown beyond its natural range have been especially damaged by attacks of this species in large masses, particularly in areas under the influence of oceanic climate. Infestations appear in the spring as new shoots sprout. Adults prefer to live on new top shoots and the degree of damage caused depends much on climatic conditions. Especially when the second generation of the insect coincides with a long dry season, as frequently happens in July, the infested top shoots often die. The loss of height increment renders the young larch trees vinable to compete with other tree species and tree tops usually become deformed through the growth of secondary shoots. The spread of T. laricivorus from its native habitat in the larch stands of south central Eiirope~to its present range of distribution appears to have been a combi- nation of factors; first, of course, was the increased cultivation of larches and the second was the supporting climatic factors. Hosts^European larch (Larix decidua) and Japanese larch (Larix leptolepis) are recorded hosts, with the latter species being more resistant. Distribution: The range of this species extends from Denmark to northern Yugo- slavia and north Italy, from Czechoslovakia across Austria to Switzerland, and from southeastern France (Saar region) across Germany and Poland into the USSR. Its actual range into the USSR is not General Distribution of Taeniothrips laricivorus Life History and Habits: The biology as studied in Germany is as follows: Ov
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