| Summary: | Northern Fennoscandia belongs to the sub-arctic environment and its forests are mostly composed of mountain birch trees (Betula pubescens ssp. czerepanovii). Outbreaks by autumn moth (Epirrita autumnata) and winter moth (Operophtera brumata) are one of the most important natural disturbance factors in the mountain birch forests, with important implications for future ecosystem functioning. If there will be a vegetation shift due to climate change or greater infestation and competition between different moth species, the moth larvae will have to feed more on alternative plant species. However, the ability of these species to feed, grow and survive on these alternative food sources is poorly understood. The aim of this study was to see if the pupae weight, the frass (excrement) amount and the survival rate differed for the autumn- and winter moth in Northern Fennoscandia, depending on which type of leaves the larvae feed on. The plant species chosen was the preferred food source mountain birch and two possible alternative food species; dwarf birch (Betula nana) and bilberry (Vaccinium myrtillus). The larvae and leaves were picked at random locations around Tromsø, northern Norway, and the autumn- and winter moth larvae were separated into different containers containing each of the three plant species. A comparison between the two moth species showed that there was a significant difference in the pupae weight, but none in the frass amount and survival rate. The autumn moth’s pupae weight and frass amount did not significantly differ between the food sources. The survival rate for autumn moth, when feeding on dwarf birch, was much higher than when feeding on mountain birch or bilberry. The winter moth’s pupae weight did however differ significantly between the food sources. The frass amount and the survival rate between the plant species did not differ, suggesting that the winter moth is a feeding generalist less likely to be limited by food availability. A greater infestation of moths in these sensitive ecosystems ...
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