[Energy turnover of water bugs]

Abstract

1. This study concerns the energy turnover of the water bug species Naucoris cimicoides (Naucoridae), Notonecta glauca (Notonectidae) and Ranatra linearis (Nepidae). The results refer to the conditions in the reed belt of the lake "Neusiedler See" in eastern Austria. 2. Population density was, using various methods, quantitatively determined for each test species. In summer the values were as follows: Naucoris 8, Notonecta 2 and Ranatra 0.5 individuals per m² in the closed reed belt. Abundance in the next spring was a halving of the initial values due to an increase in the death rate of males in winter. Generally, mortality was very high; the highest death rate for all species occurred in the first two larval stages. The total mortality, beginning at emergence and continuing until immediately after oviposition, was determined to be 91% for Naucoris, 97% for Notonecta and 99% for Ranatra. 3. Production of an average male was 211.45 cal (Naucoris), 243.24 cal (Notonecta) and 256.26 cal (Ranatra) for the entire life span. The production values determined for average females until oviposition are 316.87 cal (Naucoris), 300.79 cal (Notonecta) and 559.51 cal (Ranatra). 53.89 cal (Naucoris), 73.35 cal (Notonecta) and 264.66 cal (Ranatra) are needed for egg production. 4. Respiration was determined by volumetric measurement for all developmental stages and the imago at different times of the year. From emergence until death the following spring the O₂-consumption of an average individual was determined as 129.27 cal (♂), 156.45 cal (♀) for Naucoris, 690.66 cal (♂), 882.04 cal (♀) for Notonecta and 548.30 cal (♂), 589.16 cal (♀) for Ranatra. 5. Assimilation was calculated from production and respiration (A=P+R) for all larval and mature stages. Assimilation was determined as 340.72 cal (♂), 419.43 cal (♀) for Naucoris, 933.90 cal (♂), 1109.48 cal (♀) for Notonecta and 804.56 cal (♂), 884.01 cal (♀) for Ranatra, (cumulative values). 6. Since the mortality rates for each species were different, the energy turnover for each species varied greatly. The amount of cumulative production varied between 1.55 Kcal·10³/ha/yr (Ranatra), 6.63 Kcal·10³/ha/yr (Notonecta) and 22.96 Kcal·10³/ha/yr (Naucoris). The Naucoris population assimilated 32.74 Kcal·10³/ha/yr, the population of Notonecta 21.14 Kcal·10³/ha/yr and the Ranatra population 3.52 Kcal·10³/ha/yr. Timespan was one generation. 7. It was impossible to obtain directly a quantitative value for ingestion, so this value was calculated from other experimentally obtained values (production and respiration). It is assumed that the entire nutritional intake was assimilated the amount of excretion being insignificantly small.