Folhas de Syzygium malaccense Linnaeus (Myrtaceae): caracterização química e efeitos sobre Plutella xylostella Linnaeus (Lepidoptera: Plutellidae)

Abstract

Plutella xylostella (Plutellidae) is an important pest that attacks Brassicas cultures worldwide. Syzygium malaccense (Myrtaceae), or jambeiro, is used in popular medicine and its fruits are consumed as foodstuff. Lectins (carbohydrate-binding proteins) and trypsin inhibitors can be insecticidal agents. This work characterized the aqueous extract of S. malaccense for the presence of secondary metabolites, lectins and trypsin inhibitors, as well as for insidicidal activity against P. xylostella. Analysis by thin layer chromatography revealed the presence of polyphenols (hydrolyzed tannins), flavonoids, steroids, saponins and reducing sugars in the leaf extract, which also contained lectins (hemagglutinating activity of 64) and trypsin inhibitor. was inhibited by monosaccharides glucose and Nacetylglucosamine and neutralized by the glycoproteins fetuin and ovalbumin. The leaf extract exerted a detergent feed effect and induced mortality of P. xylostella caterpillars. The mortality rate of 80 ± 15% for the 1% leaf extract was recorded. The oviposition detergent effect was also determined for the leaf extract, since the presence of about 37 eggs was detected in the treated discs against 80 eggs recorded in the control. Exhaustive heating of the leaf extract altered the hemagglutinating and detergent food activities in a similar manner, suggesting that these can be attributed to the same protein. Exposure of leaf extract to environmental conditions for 192 h neutralized its food-producing effect. In conclusion, leaf extract of S. malaccense is a source of secondary metabolites, lectin and trypsin inhibitor, and constitutes an insecticidal agent against P. xylostella for causing mortality of caterpillars and altering their feeding and oviposition behaviors.