Studies in energetics and population dynamics of the water scorpion, Nepa rubra L. (Insecta: Hemiptera)

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Abstract
There is little information on the energy turnover of carnivorous water insects. This study concerns the energy flow through an imaginal population of the water scorpion, Nepra rubra, a water bug common in the lake “Neusiedler See” in eastern Austria. Population dynamics, production and respiration were determined from 1972 to 1975 under conditions as natural as possible. The cumulative sum of production energy is small, comprising 179.3 J for ♂♂ and 223.8 J for ♀♀, with an additional 241.6 J for reproduction. Food reserves, particularly fat accumulated in the fat body during prediapause, are utilized in winter and extensively by females during breeding the next spring. The largest fat content indicated for ♂♂ was 4.64 mg and 9.64 mg for ♀♀ (crude lipoids). The respiration rate is high even in winter. It is assumed that at this time oxygen is utilized exclusively for the oxydation of fats. Cumulative respiration energy for the adult stage was 2000.2 J for males and 3221.4 J for females. Total annual energy flow through a population of adults was about 663 kJ/100 m2 of which 596 kJ (=89%) were applied to respiration and 67 kJ (=11%) to production.