Influence of some ecological factors to abundance of seed pod weevil (Ceutorhynchus assimilis Payk.) in winter oil seed rape commercial plots.
The abiotic (air temperature), biotic (parasitism), and anthropogenic (insecticide application) factors influencing the abundance, dynamics, and injury of Ceutorhynchus assimilis on winter oilseed rape commercial plots in the Experimental Station of Lithuanian University of Agriculture were studied in 1995-96. Cold weather and frosts during the night minimized the abundance of C. assimilis on winter oilseed rape from 29 April to 21 May 1995. Insecticide application had significant negative effect on the abundance and injury of C. assimilis on winter oilseed rape plots in 1996. In treated winter oilseed rape plots, C. assimilis was absent for 2 weeks after treatment. The number of infected pods was highest (6.1%) in untreated plots (4.7% in treated plots). C. assimilis larvae were observed actively attacked by the parasitoids Trichomalus perfectus and Mesopolobus morys. Most of the active parasitoids were observed in untreated winter oilseed rape plots in 1996; they attacked 59% of weevil larvae. In treated plots, the percentage of weevil larvae attacked by parasitoids was 12.2% less.