棉铃虫经济阈值研究中的几个问题

Viewpoints on the study of economic thresholds of cotton bollworm

就华北棉区棉田棉铃虫经济阈值研究中的若干基本问题展开讨论。作者分析指出:1)用幼虫部分龄期的为害量取代全部龄期的为害量,导致经济阈值的过高估计;2)用一个世代为害期前半段或后半段的单虫为害量取代整个世代的单虫为害量,导致经济阈值的过高或过低估计;3)将以蕾为主的蕾铃被害量等同于成铃减少量,导致算出的经济阈值成倍下降;4)在确定产量损失与为害量关系的试验时,当某一处理的产量差异不显著时,不能断言这一为害量对产量的影响无经济意义,而应改进试验条件和增加重复数;5)限于现有技术条件,6月下旬左右用镊子夹或针刺方法模拟为害植株顶尖对棉花产量影响不大,远不及初孵幼虫为害顶尖的减产严重。

The authors found problems caused by some methods in the literature applied to the research of economic thresholds(ET's)of the cotton bollworm, Helicoverpa armigera (Hubner),in North China.The problems were as follows:①the ET would be over estimated by taking the damage amount by a part of instars in stead of that by the whole of instars of the larvae;②the ET would be over estimated or under estimated by taking the mean damage amount per larva in the first or second half of the time duration of a generation in stead of that in the whole of time duration of the same generation;③the ET would be under estimated by taking the number of damaged squares and bolls(mostly squares)as that of decreased sound bolls;④in order to determine the relationship between yield loss and damage amount,it is be invalid to say that a damage amount was economically of no importance,because the number of replicates was not enough or the experimental conditions were not proper;and ⑤limited by the available techniques at present,the simulated damage to the cotton plant terminals of main stems in the late June squeezed by tweezers or pricked by a pin resulted in much less yield reduction than the real damage by the newly hatched larvae.Unfortunately,these problems with the research in the literature discounted obviously the value of the work.For a more accurate ET of the bollworm,efforts should be made in the field plot experiments on the yield losses at various egg density levels on different types of soils and during several growing seasons.