Efeito da aplicai̧ão de silício em plantas de milho no desenvolvimento biológico da lagarta-do-cartucho Spodoptera frugiperda (J.E.Smith) (Lepidoptera: Noctuidae)

Abstract

The effect of the application of silicon to corn plants on the development of the fall armyworm Spodoptera frugiperda (J.E. Smith) was evaluated. Silicon treatment consisted in applying 3.2 ml of a sodium silicate solution [25-28% (w/v) SiO2] plus 96.8 ml of water into the soil at 5, 10, 15, 20 and 25 days after emergence of corn plants kept in pots. Another group of plants were grown free of silicon. Larvae were fed on leaves obtained from silicon treated plants and their mortality at the end of the 2nd larval instar, length of the larval and pupal period, and pupal weight were compared to those of larvae fed on normal leaves. No effect of silicon was observed on the length of larval and pupal phase, pupal weight and mortality of pupae. However, increased mortality and cannibalism were registered in groups of fall armyworm at the end of the 2nd instar and greater mortality of the larvae was seen at the 2nd and 6th instars fed on silicon-treated corn plant leaves in comparison with the control. The jaws mandibles of fall armyworm at the 6th instar showed marked wear on the incisor region when in contact with leaves with higher silicon content. Silicon application can make fall armyworm feeding difficult, causing higher mortality and cannibalism, thus increasing plant resistance to this species.