Abundance of cabbage aphid and their natural enemies in differently fertilized and covered with agro-film white cabbage.

The investigations were carried out at the Institute of Horticulture in 2003–2004. The occurrence of cabbage aphid (Brevicoryne brassicae L.) and parasitoid from Braconidae family, also predators from Syrphidae and Cecidomyiidae families were observed on the ecologically grown white cabbages. Plots non-fertilized and covered and fertilized with manure and covered with agro-film were compared. In both experimental years, the abundance of aphids was higher on manure-fertilized than on non-fertilized cabbage plants, whereas in 2004, the pest incidence was significantly higher on manure-fertilized plants. Main aphid parasitoid Diaeretiella rapae M’Intosh (Braconidae) was most common during all the period of observation. Aphidoletes aphidimyza Rond. (Cecidomyiidae) was found in cabbage aphids in 2004, on cabbages covered with agro-film. Covering plants with agro-film does not reduce the risk of B. brassicae infestation. Moreover, microclimate may become more favorable for pests and sometimes for predators to develop. We calculated correlation and regression coefficients to estimate the relationship between the number of cabbage aphids and intensity of D. rapae parasitation.