In the research of voracity of syrphid larvae it was found that the number of aphids Aphis Jabae Scop. eaten by larvae oscillated between 300-800 specimens depending on the syrphid species. Larvae of Syrphus ribesii (L.) appearred to be the most voracious. It was found that predator-prey ratio from 1:25 to 1:50 was the most effective at Episyrphus ba/teat us (Deg.) and Sphaerophoria scripta (L.) larvae in Aphis fabae control on broad bean.

The paper presents the dynamic characteristics of a continuous tank bioreactor for microbiological process, with a developed predator-prey food chain. The presence of the predator microorganism considerably influences the position and stability character of steady-states. There appears to exist a wide range of unstable steady-states and high-amplitude oscillations of state variables. Without automatic control, the system can operate only in unsteady conditions. From technological point of view, this circumstance is unfavorable. It was shown that oscillations can be removed by employing automatic control with continuous P or PI controllers. Moreover, the use of a controller with integrating element causes removal of the predator from the bioreactor. The paper discusses an application of this phenomenon for practical purposes.