The value of two Collembola species as food for a linyphiid spider

Egg production by the cereal spider Erigone atra was used as a fitness para meter for evaluating the food quality of two species of Collembola: Folsomi a fimetaria and Isotoma anglicana. Drosophila melanogaster was used as refe rence prey. We tested the hypothesis that due to differences in food qualit y, the two Collembola species would affect the reproduction of the spider d ifferently. The quality ranking of the prey types turned out as: I. anglica na > D. melanogaster > F. fimetaria. With F. fimetaria alone, spiders were unable to maintain reproduction. E. atra was more efficient in utilising I. anglicana and D. melanogaster. Thus, daily consumption rates of I. anglica na were lower in spite of higher egg laying rates by E. atra. A mixed diet of F. fimetaria and D. melanogaster resulted in a lower reproductive output than a pure diet of D. melanogaster, indicating a toxic element in F. fime taria. In the mixed diet F. fimetaria had a negative influence on the consu mption capacity of the spider towards D. melanogaster, while D. melanogaste r had a positive influence on the consumption capacity towards F. fimetaria . It is concluded that a high abundance of I. anglicana may support a high reproductive output of E. atra, while the presence, of F. fimetaria in fiel ds may reduce the spider's reproductive output.