Predator–Prey Relationships in a Two-Species Toxicity Test System

In a two-species toxicity test system survival and reproduction of both the predatorHypoaspis aculeifer(Gamasida) and the preyFolsomia fimetaria(Collembola) were studied after 21 days of residual exposure to a soil contamination of the insecticide dimethoate. Additional experiments were run to analyze which species–species and compound–species relationships determine the outcome of this two–species experiment. Number of adultF. fimetariawere reduced by both predation and dimethoate exposure, whereas mites preyed less efficiently on adults than on juveniles. At 0.357 mg dimethoate/kg soil, numbers of juvenileF. fimetariawere mainly reduced by predation on adults and juveniles. At 0.7 mg/kg, an additional dimethoate effect was found, which was attributed to an effect on the reproduction ofF. fimetaria, mainly due to lethality of adults. It was reasoned that lethal effects on juvenile springtails are less important. AdultH. aculeiferwas not affected by dimethoate exposure, whereas numbers of juvenileH. aculeiferdemonstrated a decline only at the highest concentration of 0.7 mg/kg. It is hypothesized that this latter effect is possibly due to food depletion caused by a decreased availability of prey, rather than to the lethal effects of dimethoate on juvenile mites. Such a secondary effect of a pesticide application could not have been derived from a single-species toxicity experiment and demonstrates the additional value of a two-species toxicity test system.