甜菜夜蛾引起的青菜产量损失及其防治指标研究

Studies on the pakchoi yield loss caused by beet armyworm and the economic thresholds

利用接虫的方法，测定了秋季青菜不同生育期甜菜夜蛾幼虫数量与产量损失率的关系。结果表明：在青菜不同的生育期，随着接入虫数的增加，青菜产量均逐渐下降。青菜不同生育期对甜菜夜蛾危害的敏感性不同，以青菜前期较为敏感，低虫量的甜菜夜蛾危害就可能引起青菜产量明显的损失，因而前期的防治最为关键。青菜前期以低龄幼虫为主时防治指标为单株虫量0．1头左右，以中高龄幼虫为主时防治指标为单株虫量0．05头左右；青菜后期以低中龄幼虫为主时防治指标为单株虫量0．2～O．3头，以高龄幼虫为主时防治指标为单株虫量0．5头左右。

The relationships between the yield losses of pakchoi at different growth stages in au- tumn and the larval quantity of beet armyworm were investigated by inputting various larval quanti- ties. The results showed that the pakchoi yields at different growth stages gradually decreased with the number of input larvae increasing. The susceptibility of pakchoi to beet armyworm was various at dif- ferent growth stages. The early-stage pakchoi was the most susceptible,and so controlling beet army- worm at the early stage was critical. It was suggested that at the early stage of pakchoi growth the lar- vae should be controlled when the density of 2nd - 3rd instar larvae reached 0.1 head per plant or that of 4th - 5th instar larvae reached 0.05 head per plant,and at the later stage of pakchoi growth the lar- vae should be controlled when the density of 2nd - 3rd instar larvae reached 0.2 - 0.3 head per plant or that of 4th - 5th instar larvae reached 0.5 head per plant.