Zum Energieumsatz phytophager Insekten im Buchenwald. II

Abstract

The energy turnover of weevil populations ofPhyllobius argentatus L.,Polydrosus undatus F., andStrophosomus sp. was investigated in a 123 years old (1970) beech forest in special consideration of their soil-living rhizophagous larvae (results of the energy turnover ofStrophosomus sp. imagines, see Grimm, 1973). Life-Cycle. P. argentatus with five larval stages develops in one year. The imago lives for about 30 days in the stand layer (May to August). During 12 to 15 monthsStrophosomus sp. has four larval stages. The imago lives from September onward for 9\2-12 months (see Grimm, 1973). The four larvae ofP. undatus develop in a space of 18 months. The imago leaves the soil after a 7 or 8 month lasting stay and lives in the stand layer for 45 days (April to July).Strophosomus sp. andP. undatus hibernate as larval stage 4 (1. way of development) or as stage 3 (2. way of development). Abundance. Abundance of larvae and pupae were determined by square samples and direct sorting. In the case ofP. undatus andP. argentatus the numbers of beetles emerging were determined by means of eclector catches (emergence traps). Shaking samples yielded data about abundance of weevils in crown layer. The period of activity of weevils on the stems was determined with arboreal photoeclectors. Bioenergetic Results. The investigations of energy turnover produced the following results: Average individual Populations The weevil populations 1969–1970 (71) assimilated:20,161 · 10³kcal/ha (P. argentatus), 10,703 · 10³ kcal/ha (Strophosomus sp., 1. and 2. way of development), and 3,865 · 10³ kcal/ha (P. undatus, 1. and 2. way of development), till the end of the pupal stage. Until death of imagines the populations assimilated 21,129 · 10³kcal/ha (P. argentatus) and 4,009 · 10³ kcal/ha (P. undatus). Production of imagines (biomass of imagines emerging from soil) The production of imagines (mean 1968–1972,B _1a) amounted to about 8,118 · 10³ kcal/ha·yr (P. argentatus) and about 0,997·10³ kcal/ha·yr (P. undatus). 5 to 10 photo-eclectors were found to be the optimal number for determining the production of imagines. Flux of energy from roots of beech to populations of rhizophagous weevils was discussed.