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<P align="justify"> Autumnal moth (<i>Epirrita autumnata</i>) is off-white in colour with dark patterning on the wings. It flies in August and September. Autumnal moths winter in the form of eggs, and the larvae hatch in spring. The larvae feed off the leaves of mountain birches in northern Lapland in summer, and they pupate after 4-6 weeks. At approximately ten-year intervals, usually for periods of about 2-3 years, the larvae of the autumnal moth appear in vast numbers. They only occasionally cause damage, however, and the damage is usually local. When they do, they leave only the dead trunks of the mountain birches standing. It may take decades or even centuries before the stands of mountain birches return to their former state. In addition to its limited local nature, it is characteristic of the ruin caused by the autumn moth larvae that it affects mainly older stands of mountain birch and leaves the younger trees untouched. The trees react to being eaten by the larvae after a delay of 2-4 years. The quality of the leaves deteriorates in the following years, and the larvae of the autumn moth no longer thrive.</P> <P align="justify"> Parasites also cause the populations of the autumn moth at its highest to decline. The severity of the winter governs the populations locally. The eggs die if the air temperature falls below -36ºC.</P> <P align="justify"> In order for the autumn moss to increase to plague proportions, a forest of unbroken birch is required. Such woods are only found in the fell regions of Norwegian, Swedish and Finnish Lapland. In southern Finland, no such damage has been done to birch stands although the autumnal moth is very common there.</P>
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