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 d evelop earthworm feeds which might act as a microbial carrier in earth worm-mediated dispersal of beneficial microorganisms in soil. A circul ar choice chamber containing 18 feeding stations was used to assess th e food-type preference of four earthworm species (Aporrectodea caligin osa, A. longa, Lumbricus rubellus, L. terrestris). Representatives of each species were presented with four types of organic matter (cow dun g, 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 alon e was also tested in the same chamber. The nine types of potential foo d 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 ear thworm species showed a strong preference for pure mineral soil over p ure organic matter. Also, mineral-organic mixtures were clearly prefer red to pure organic sources, with I:af litter + soil being the preferr ed mixture for all four earthworm species tested. In addition, cow dun g + soil and sewage sludge + soil were acceptable to all species excep t A. caliginosa. Inoculation of the food stuffs with Pseudomonas corru gata 2140R lux8 did not deter the earthworms from feeding and earthwor m casts contained from 10(7) to 10(9) cfu g(-1) wet wt. The choice cha mber method offers a simple, rapid and inexpensive test for studying f ood preferences of earthworms for various applications. (C) 1997 Elsev ier Science Ltd.