Influence of mineral soil on the palatability of organic matter for lumbricid earthworms: A simple food preference study

The food-preference behaviour of earthworms was examined in order to develop earthworm feeds which might act as a microbial carrier in earthworm-mediated dispersal of beneficial microorganisms in soil. A circular choice chamber containing 18 feeding stations was used to assess the food-type preference of four earthworm species (Aporrectodea caliginosa, A. longa, Lumbricus rubellus, L. terrestris). Representatives of each species were presented with four types of organic matter (cow dung, sheep dung, decomposed leaf litter, sewage sludge) either alone or mixed 1 to 4 (on a dry weight basis) with a sandy loam soil; soil alone was also tested in the same chamber. The nine types of potential food were each inoculated with Pseudomonas corrugata 2140R lux8 at a rate of 10(7) cfu (colony forming units) g(-1) wet wt of material. All earthworm species showed a strong preference for pure mineral soil over pure organic matter. Also, mineral-organic mixtures were clearly preferred to pure organic sources, with I:af litter + soil being the preferred mixture for all four earthworm species tested. In addition, cow dung + soil and sewage sludge + soil were acceptable to all species except A. caliginosa. Inoculation of the food stuffs with Pseudomonas corrugata 2140R lux8 did not deter the earthworms from feeding and earthworm casts contained from 10(7) to 10(9) cfu g(-1) wet wt. The choice chamber method offers a simple, rapid and inexpensive test for studying food preferences of earthworms for various applications. (C) 1997 Elsevier Science Ltd.