The effectiveness of Tetrastichus triozae Burks (Hymenoptera: eulophidae) as a biological control agent of Paratrioza cockerelli (Sulc.) (Homoptera: psyllidae) in North Central Colorado

Abstract

This study was undertaken to determine some of the factors affecting the value of the parasite, Tetrastichus triozae Burks, as a control agent of the potato psyllid, Paratrioza cockerelli (Sulc.), in the potato growing areas of Weld and Morgan counties. Field observations revealed that the parasite appeared after the spring psyllid infestation had declined and that the parasite population had declined by the time the fall psyllid infestation had built up again. Parasite pupal mortality ranged from 38-100% in the field populations. The time of appearance and high pupal mortality appeared to reduce the effectiveness of the parasite. In the laboratory, the parasite and psyllid cycles were synchronized in relation to time of development. Because the parasite attacked only fourth and fifth instar psyllid nymphs, the parasite could not prevent psyllid yellows from killing the potato plants. This makes mass releases economically unfeasible in commercial fields. However, the parasite was efficient in the laboratory at controlling the psyllid populations indicating that the parasite might be of value as a biological control agent in the over-wintering areas. Parasite dispersal was very rapid when the distance between host plants was 5 feet or less; distances of 7-30 feet greatly reduced dispersal. This may account for localization of the parasites. The cause of the high pupal mortality was not ascertained, but disease and predators may have been partially responsible.