| Abstract: | The results of four experiments on biological control of Frankliniella occidentalis on flowering Saintpaulia ionanfha and one on pelargonium are presented. Three species of predatory mites were used for the experiments: Amblyseius barkeri, and two soil-dwelling species Hypoaspis aculeifer and H. miles. Three releases each of 15 H. miles per saintpaulia plant at weekly intervals did not have any effect on the pest population. In two experiments on saintpaulia, 10 females of H. aculeifer per plant were released weekly for a period of 10 weeks. The increase of thrips population was slowed down for some weeks and population peaks were diminished. However, this treatment failed to keep the pest at a low level. In one experiment, 15 A. barkeri per saintpaulia plant were released weekly for 10 weeks. Thrips population dynamics was slowed down for about 4 weeks, but again the treatment failed to keep the pest at a low level. In one experiment on pelargonium, 15 A. barkeri per plant were released fortnightly for 10 weeks. An effect was obvious in both replicates. Pest populations hardly increased on the plants treated with the biocontrol agent but increased significantly in the controls. The reasons for these results and differences are discussed. The suitability of these three species for production and use as biocontrol agents is discussed. |
