Infestation by Cerotoma arcuata (Olivier) (Coleoptera: Chrysomelidae) larvae on Phaseolus bean with mulching or intercropped with maize or cowpea

摘要

> size="2" face="Verdana, Arial, Helvetica, sans-serif">The bean leaf beetle Cerotoma arcuata is a legume leaf eater and its larvae feed on roots and also nodules where nitrogen fixation occurs. The attack of larvae to nodule may result in more damage to the bean crop than the consumption of leaves by adults. This study was conducted under field conditions to test the effects of C. arcuata infestation on Phaseolus bean with or without straw mulching or intercropped with maize or cowpea. Nodulation, growth and grain production when intercropping with cowpea did not differ from the control. The insect barrier formed by the maize’s high density failed, probably due to the early infestation by C. arcuata, as well as shading by the rows of maize, thereby reducing grain yield. Consumption of nodules was higher on the Phaseolus bean with or without intercropping than on the treatment with straw mulching. The physical barrier imposed by straw mulch probably acted by reducing oviposition directly on soil and drying the eggs laid above the straw, resulting in a smaller percentage of punctured nodules and consequently increasing nodule number and dry weight, root dry weight and grain yields. Intercropping with maize and cowpea did not reduce Phaseolus bean infestation by C. arcuata but straw mulching applied before infestation reduced damage caused by larvae to the nodules, increasing N₂ fixation and grain yields.