Predation of Amaranthus quitensis HBK seeds in soybean crops: Influence ofthe tillage system

The objective was to evaluate the losses of the superficial bank of Amarant hus quitensis seeds, due to insect predation, in a soybean crop and in the subsequent fallow, in two tillage systems. Experiments were conducted durin g 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 th e number of remaining seeds was registered every 15 days. Pitfall traps wer e used to identify insects species occurring in the field and to estimate t heir abundance. The carabid Notiobia cupripennis was captured in pitfall tr aps, the higher population found during March (4.5 and 5.8 insect/trap in c onventional 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 significantl y different as to abundance and predation. No significant differences were found from April to June, and the number of insects and predation rates dec reased. There was a positive correlation between the predation rates and th e values of insect abundance in both years.