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The time series of Phytobia abundance on two host species, B. pendula and B. pubescens, in two host stands: Peikkola population, years 1929–1993, B. pendula 15 trees, B. pubescens 10 trees; Valtatie population, years 1947–1993, B. pendula 16 trees, B. pubescens 14 trees. The points indicate the annual average numbers of Phytobia per tree.
