On the influence of different soil cultivation practices in autumn and spring on the population development of the western corn rootworm Diabrotica virgifera virgifera LeConte (Col.: Chrysomelidae)

It can be expected that intensity and depth of soil cultivation have an impact on the eggs of Diabrotica virgifera virgifera, which are predominantly positioned 10 to 15 cm below soil surface. Main aim of this study was to investigate the relationship between different cultivation measures in autumn and spring and the hatching of adult D. virgifera virgifera as well as the maize root damage, caused by larvae. Gauze covered hatch-cages (2 per plot) were used to count the emerged imagines. Variants: Plough and grub, both 25 cm working depth, in autumn and superficial tillage with disc-harrow in spring. The trials were performed on fields with a significant natural D. virgifera virgifera infestation, in West Romania. The number of hatched adult D. virgifera virgifera was unsteady in the different years and did not correlate with soil-cultivation practices. This finding can be explained with the different climatic conditions in the single years. The maize-root damage under the hatch-cages was not significantly different between variants. This may on the one hand result from the limited number of samples (2 cages per plot) on the other hand also from the artificial growth circumstances for the maize under the small cages. The maize-root damage assessed in the surrounding plots was significantly lower in the plough-variant compared to those in the grubber- and disc-harrow-plots, in two of three years. A summary of all data achieved in three years, showed a significant correlation between the number of adult D. virgifera virgifera and the maize-root damages in the field (p=0.0001, r=0.605).