Effect of temperature and plant size on the infestation dynamics of oilseed rape plants by Baris coerulescens Scop. (Col., Curculionidae) in field conditions

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Abstract
The plant infestation dynamics of winter oilseed rape, Brassica napus L. var. oleifera Metzger, by Boris coerulescens was investigated during a 3 years study in field conditions. Each year, plant infestation started at the end of March and reached a maximum ca. 23 June, then dropped drastically. Mortality was very low up to the maximum of population then increased abruptly. The main cause for mortality was plant desiccation caused by fungal diseases, harvest or degeneration of the cortex 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 logistic curve from the beginning to the end of the increase in population. Egg accumulation in plants is linearly linked to degree days during most 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 density dependent. The infestation level at harvest is a very poor indicator of the overall level reached during the whole plant cycle because of higher mortality in big, heavily infested plants than in less infested small ones.
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