水稻穗期大螟危害习性初步观察

于2009年常规中稻的蜡熟前期、中期和黄熟期、枯熟期,分别取样观察大螟Sesamia inferens Walker的钻蛀危害习性。结果发现:单株螟害的蛀孔数一般为2～3个,多的达5个,而且表现白穗株>枯穗株>虫伤株。螟害株的蛀孔部位随着稻穗趋向成熟和大螟虫龄的增大,逐渐由稻株的中上部节间向中下部节间转移。其中,白穗株与枯穗株有70%以上的蛀孔分别分布于稻株由上向下的第1～3与3～5节间上;在水稻的这4个生长时期中,虫伤株有90%左右的蛀孔分别分布于稻株由上向下的第1～3、1～4和2～5、3～5节间上,全株虫量有85%以上依次分布于第1～3、2～4和3～5、3～5节间上,单株虫量4个时期最高分别为18、6、3、2头,同一节间内的4个时期最高虫量分别为12、5、1、1头;单个节间有多头螟虫时,80%以上为1～3龄幼虫。随着稻穗趋向成熟,白穗株和枯穗株上的虫量均逐渐下降,而虫伤株上的虫量则相对稳定或有上升的趋势;至枯熟期后,虫伤株的有虫株率和有虫孔率均稳定在30%以上。

Preliminary observation on damage habit of rice stem borer ( Sesamia inferens ) at rice heading stage

In order to observe crop damage caused by Sesamia inferens Walker,samples of conventional rice crops were collected at different stages of growth（early dough,middle dough,yellow ripeness and wilting stages） in 2009.The number of wormholes in single plants was usually in the range of 2 ～ 3 but could be as high as 5.Plant damage could be ranked in increasing order as follows：white head,withered ear and insect damaged.With the ripening of rice panicles and increasing insect instar,the location of wormholes changed from the upper-middle to the lower-middle of rice plants.More than 70% of wormholes in white headed and withered plants were distributed over the first to third and third to fifth internode from the top to down.In the four growth periods,about 90% wormholes were distributed over the first to third internode,first to fourth internode,second to fifth and third to fifth internode.More than 85% of worm numbers in whole plants were distributed in the first to third internode,second to fourth internode,third to fifth and third to fifth internode.The number of insects found in individual plants was 18,6,3 and 2 and within the same internode was 12,5,1 and 1.When there was more than one insect in a single internode, 80% of these were first to third instar larvae.With the ripening of rice panicles,insect numbers in white headed and withered ear plants reduced gradually,but those in insect damaged plants either remained relatively stable or increased.After the wilting stage,both the infection rate and wormhole rate in insect damaged plants was consistently 30%.