密度对甜菜夜蛾幼虫色型分化的影响

Effect of density on the larval color morph differentiation in beet armyworm Spodoptera exigua

为明确田间甜菜夜蛾Spodoptera exigua幼虫产生绿色型和黑化型的色型分化原因,在田间系统调查黑化型幼虫所占比例及其与虫口密度的关系,在室内测定不同饲养密度对甜菜夜蛾幼虫色型分化的影响和色型分化敏感龄期,以及视觉、嗅觉和触觉对幼虫色型分化的影响。结果表明,田间甜菜夜蛾1~3龄幼虫均为绿色型,4~5龄幼虫同时存在绿色型和黑化型;在甘蓝上,4龄幼虫中黑化型个体所占比例为21.14%,5龄幼虫中黑色型个体所占比例为28.53%,在辣椒上,4龄幼虫中黑化型个体所占比例为20.54%,5龄幼虫中黑色型个体所占比例为33.88%。随着百株虫量的增加,甘蓝和辣椒上黑化型幼虫所占比例呈现升高趋势。室内研究发现,随着甜菜夜蛾幼虫饲养密度的增加,黑化型幼虫占比显著升高,当饲养密度达到5头/盒时趋于稳定,体色等级指数为3.47;3龄是甜菜夜蛾幼虫色型分化的敏感龄期;视觉和嗅觉刺激对甜菜夜蛾幼虫黑化无显著影响,而触觉刺激显著促进幼虫黑化,甘蓝叶片碎片和白色聚酯纤维的摩擦处理导致幼虫体色等级指数分别显著升高68.59%和71.79%,表明触觉刺激信号对甜菜夜蛾的密度依赖性黑化有显著促进作用。

To clarify the reasons for the differentiation of the green and black morphs of beet armyworm Spodoptera exigua larvae in the field,field investigations were carried out to determine the proportion of black morph and its relationship with larval density.In the laboratory,the effects of different feeding densities on color morph differentiation and the sensitive period for morph differentiation as well as the effects of visual,olfactory,and tactile stimuli on morph differentiation were determined.The results showed that,in the field,the first to third instar larvae of S.exigua were all green morphs,while the fourth and fifth instar larvae included both green and black morphs.In cabbage hosts,the proportion of black morph was 21.14% in the fourth instar larvae and 28.53%in the fifth instar larvae,respectively.In pepper hosts,the proportion of black morph was 20.54% in the fourth instar larvae and 33.88% in the fifth instar larvae,respectively.With increasing larval density,the proportion of black morph in both cabbage and pepper hosts increased.In-depth laboratory studies found that the proportion of black morph increased significantly with increasing feeding densities,but reached stability at a density of five larvae per box,with a body color index of 3.47.The third instar was identified as the density-sensitive period for color morph differentiation in S.exigua larvae.Visual and olfactory stimuli had no significant effect on blackening,while tactile stimuli significantly promoted blackening.Frictional treatment of cabbage leaf fragments and white polyester fibers resulted in significant increases in body color index by 68.59% and 71.79%,respectively,indicating that tactile stimulation signals have a significant promoting effect on density-dependent color morph differentiation in S.exigua larvae.