1　虫源发生了转移虫源基数为下代发生的主要预测依据之一 ,过去棉田残虫是下代发生的主要虫源 ,预报时往往忽视粮食、蔬菜等作物田基数的重要性。近年随着抗虫棉 (转 Bt基因棉 )的普遍种植和棉花面积的减少 ,棉田残虫在虫源中所占的比例明显减少 ,而其它作物田残虫量明显升高 1 The origin of insect pest occurrence The base of insect pest incidence is one of the major predictors of the occurrence of the next generation. In the past, the cotton insect pest was the main source of the next generation. In forecasting, the importance of the base of crops such as grain and vegetables was often neglected. In recent years, with the widespread planting of cotton (transgene Bt cotton) and reduction of cotton area, the proportion of cotton beetles in the insect sources significantly decreased while that of other crops increased significantly