Cocoon production of Aporrectodea longa Ude and Aporrectodea rosea savigny(Oligochaeta; Lumbricidae) in a Danish grass field

I describe a method to study the reproductive rate of earthworms in the fie ld. The method is based on a detailed knowledge of the influence of tempera ture on the development of earthworm cocoons. This relationship [R(T)] was described for populations of Aporrectodea longa and A. rosea that were stud ied in a field experiment from 1 May to 6 June, 1997. Soil temperature was measured throughout the study and on 6 June the density of cocoons was esti mated. The sampled cocoons were incubated in the laboratory and their hatch ing distribution was recorded. Based on R(T), the average development time in the field of cocoons produced on 1 May was predicted, and the hatched co coons could thus be scored as either produced during the study, or before. This made it possible to estimate the density of cocoons produced during th e study. The density of adults was also estimated by soil sampling during t he study, and finally the reproductive rate could be calculated as density of cocoons divided by density of adults. Using this method the reproductive rate (viable cocoons) of A. longa was estimated to 0.09 +/- 0.04 cocoon ad ult(-1) d(-1) (mean +/- S.D., n = 4), corresponding to a cocoon production throughout the study of 3.3 +/- 1.6 adult(-1). The reproductive rate of A. rosea was estimated to 0.20 +/- 0.06 cocoon adult(-1) d(-1), corresponding to 7.2 +/- 2.1 adult(-1). The average soil temperature was 10 degrees C. Th ese results confirm results of previous studies indicating that the reprodu ctive rate of A. longa is low in comparison with other earthworm species. O n the other hand, the results suggest that the reproductive rate of A. rose a under natural conditions may be much higher than assumed. (C) 1999 Elsevi er Science Ltd. All rights reserved.