THE NUTRITIVE-VALUE OF 2 SPECIES OF MICROORGANISMS TO THE EARTHWORM EISENIA-FETIDA

The nutritive value of the cyanobacterium Spirulina platensis and the alga Chlorella minutissima to the earthworm Eisenia fetida was investi gated in laboratory feeding trials to determine the potential role of microalgae in earthworm diet in soil. The effects of some chemical cha racteristics of microalgae were evaluated on the survival and growth O f individual earthworms in Petri dishes containing cellulose. The suit ability of microbial biomass to support growth and reproduction of gro ups of earthworms was evaluated in larger containers. Earthworms grew in dishes containing S. platensis, but were unable to grow on a diet c omposed of C. minutissima. Intact algal cells in cellulose casts indic ated an inability of earthworms to digest them. The factors which affe cted earthworm growth in dishes containing S. platensis were the mode of application and the degree of washing of microalgal biomass. Top-fe eding resulted in weight gain which was 4.6 times greater than that of mixed feeding. Feeding on unwashed microalgae resulted in 3.5 times i ncrease of weight gain relative to feeding on washed microalgae either using live or dead microorganisms. Combined antibiotic treatment of S . platensis or earthworms or both had no effect on earthworm growth. I n combination with macroscopic observations of gut contents and micros copic observations of earthworm casts, these results indicate that ear thworm growth was caused by assimilation of this microbial species. Gr owth and reproduction of earthworm groups fed with Spirulina in cellul ose provided evidence that populations can be sustained and developed with a diet composed of cyanobacteria in soil. Compared to conventiona l substrates, i.e., animal manures, growth of parental worms was slowe r the first 4 weeks of incubation, but significantly higher than those in horse manure after 8 or 12 weeks. The mean net reproductive output was greatly reduced in Spirulina as a result of high variability in t he number of hatchlings. The differences in the number of hatchlings b etween groups fed with Spirulina were related to differences in the nu mber and weight of cocoons produced.