A particularly advantageous method of monitoring the flight and calculating the median was used. An example is given in order to understand better the calculation. The medians show that the timing is similar at different latitudes despite local phenological differences. The difference in median flight times between Finland and the Czech Republic was five days on average, but phenological differences are about a month, shown by a comparison of temperatures, the monitoring of buds on spruce, and

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... y the stage of the carrot plants. During the attack by T. apicalis the carrot plants are younger towards north what is unusual in Psyllidae. In extreme north locations as Finland the genetic triggering for flight could not be realised by the strong declining of temperatures. Flight occurs here substantially later as to local photoperiodicity but is the earliest as to phenology, including carrot plants. The very small plants during flight are much more damaged here than the well-developed plants in central Europe.