EFFECT OF TEMPERATURE AND PLANT SIZE ON THE INFESTATION DYNAMICS OF OILSEED RAPE PLANTS BY BARIS-COERULESCENS SCOP (COL, CURCULIONIDAE) IN FIELD CONDITIONS

The plant infestation dynamics of winter oilseed rape, Brassica napus L. var. oleifera Metzger, by Balls coerulescens was investigated durin g a 3 years study in field conditions. Each year, plant infestation st arted at the end of March and reached a maximum ca. 23 June, then drop ped drastically. Mortality was very low up to the maximum of populatio n then increased abruptly. The main cause for mortality was plant desi ccation caused by fungal diseases, harvest or degeneration of the cort ex of the root. Mortality was higher in big plants than in small ones. Plant infestation can be described as a function of time by a logisti c curve from the beginning to the end of the increase in population. E gg accumulation in plants is linearly linked to degree days during mos t of the ascending phase of plant infestation. The number of immature individuals per plant (from egg to nymph) is linearly linked to plant size: as measured from the root crown diameter. The relationship is de nsity dependent. The infestation level at harvest is a very poor indic ator of the overall level reached during the whole plant cycle because of higher mortality in big, heavily infested plants than in less infe sted small ones.