Differences among five amaranth varieties ( Amaranthus spp.) regarding secondary metabolites and foliar herbivory by chewing insects in the field

In this study, we determined the abundance of secondary metabolites present in leaves of five varieties of Amaranthus , described the community of chewing insects observed in the foliage and also quantified damage by folivore insects in the field. Three flavonoid glucosides (rutin, nicotiflorin and isoquercitin), nine phenolic compounds (coumaric, vanillic, caffeic, syringic, ferulic, sinapic, protocatechuic, salicylic and 4-hydroxybenzoic acid) and three betalains (amaranthine, iso-amaranthine and betanin) were found to be present in amaranth leaves. Flavonoids appeared in of all varieties analyzed, with rutin being the most important. Betalains occurred only in some varieties and at different proportions, and nine phenolic acids were observed in all the varieties, with the exception of sinapic acid. Significant differences in the chemical composition of the varieties were noted. A total of 17 species of chewing phytophagous insects were observed through visual counting in Amaranthus plants, with the order Coleoptera being the most important and having the highest diversity of species. The degree of herbivory differed significantly among the varieties. Multivariate regression analysis indicated that the eight analyzed compounds detected in the plants had significant linear relationships with herbivory in the field. However, to draw any conclusions relating the amount of any compound to the degree of herbivory damage is premature at this stage of the research.