Effect of density on the larval color morph differentiation in beet armyworm Spodoptera exigua
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 pro-moting effect on density-dependent color morph differentiation in S.exigua larvae.
万方数据
维普
