SUITABLE PREDATOR-PREY RATIOS FOR THE USE OF CHRYSOPERLA-CARNEA (STEPHENS) EGGS AGAINST APHIDS ON SUGAR-BEET UNDER LABORATORY AND FIELD CONDITIONS

The influence of releases of Chrysoperla carnea (Stephens) eggs on the development of the population of Aphis fabae (Scop.) was analyzed on sugar beet at various predator-prey ratios (1:15, 1:10, 1:5) under bot h laboratory and field conditions. Under laboratory conditions, a redu ction of aphids could only be achieved at a predator-prey ratio of 1:5 , while the others (1:10 and 1:15) resulted in an increasingly severe damage to the plants due to high average numbers of up to 387 aphids p er plant. Of the released eggs, a maximum of 26.1% could be found ass larvae. Under field conditions, a predator-prey ratio of 1:5 provided a satisfactory protection of the plants for a period of approximately 2 weeks with average numbers of aphids per plant being less than 10. W ith other predator-prey ratios, the success, which was also influenced by the right timing of the release, was less visible. A maximum of 23 .1% of the released eggs could be found as larvae. Other natural enemi es of aphids found belonged to Coccinella and Syrphidae and showed alm ost the same abundance in each of the predator-prey ratios used in the experiment.