The objective was to evaluate the losses of the superficial bank of Amaranthus quitensis seeds, due to insect predation, in a soybean crop and in the subsequent fallow, in two tillage systems. Experiments were conducted during 1994/95 and 1995/96. To estimate predation rates, trays covered with wire meshes to prevent rodent predation, and with fine sheer net (tulle) in the control treatment were used; 100 weed seeds were sown in each tray, and the number of remaining seeds was registered every 15 days. Pitfall traps were used to identify insects species occurring in the field and to estimate their abundance. The carabid Notiobia cupripennis was captured in pitfall traps, the higher population found during March (4.5 and 5.8 insect/trap in conventional tillage and 2.7 and 3.3 insect/trap in no-tillage). The highest predation rates was also registered in March (5.6% and 8% in conventional tillage and 2.7% and 3.8% in no-tillage) and both systems were significantly different as to abundance and predation. No significant differences were found from April to June, and the number of insects and predation rates decreased. There was a positive correlation between the predation rates and the values of insect abundance in both years.
Notiobia cupripennis; seed bank; tillage; weed
