Sammendrag
1. Outbreaks of herbivorous insects can have large impacts on regional soil
carbon (C) storage and nutrient cycling. In northernmost Europe, population outbreaks
of several geometrid moth species regularly cause large-scale defoliation in subarctic
birch forests. An improved understanding is required of how leaf C and nutrients are
processed after ingestion by herbivores and what this means for the quantity and quality
of different materials produced (frass, bodies).
2. In this study, larvae of two geometrid species responsible for major outbreaks
(Epirrita autumnata and Operophtera brumata) were raised on exclusive diets of
Betula pubescens var. czerepanovii (N. I. Orlova) Hämet Ahti and two other abundant
understorey species (Betula nana, Vaccinium myrtillus). The quantities of C, nitrogen
(N) and phosphorus (P) ingested and allocated to frass, bodies and (in the case of C)
respired were recorded.
3. Overall, 23%, 70% and 48% of ingested C, N and P were allocated to bodies,
respectively, rather than frass and (in the case of C) respiration. Operophtera brumata
consistently maintained more constant body stoichiometric ratios of C, N and P than
did E. autumnata, across the wide variation in physico-chemical properties of plant diet
supplied.
4. These observed differences and similarities on C and nutrient processing may
improve researchers’ ability to predict the amount and stoichiometry of frass and bodies
generated after geometrid outbreaks.
Consumer-driven nutrient recycling, ecological stoichiometry, geometrid
moth, homeostasis, stable isotope, subarctic birch forest.
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