Avaliação da atividade inseticida do colmo da Guadua angustifolia Kunth contra Tribolium castaneum (Herbst)

Abstract

Tribolium castaneum, an insect in the order Coleoptera, is an important agent responsible for great economic damage to food grains stored in South America. To control this pest, more efficient methods are sought, less toxic to the environment and compatible with volumes of stored grains. Plants extracts and isolated lectins have shown insecticidal properties to different orders of insects and for this reason have been studied by several research groups. Brazil has the largest native bamboo forest diversity in the Americas. Among identified bamboo species, Guadua angustifolia is a fast-growing grass that offers raw materials explored in the areas of landscaping and civil construction. Thus, the present study aimed to analyze the effect of extract and lectin isolated from the stem of G. angustifolia in adult insects of T. castaneum. For this, the crude extract was prepared in 50 mM Tris-HCl, pH 8.0 of the pulverized bamboo stem. Subsequently, phytochemical analysis, protein quantification and identification of lectin presence were performed. The antioxidant potential of the extract was evaluated. Then, the extract (25 mg, 50 mg and 100 mg) was evaluated for insecticidal activity, analyzing the nutritional parameters and survival rate of the insects treated during the 30-day bioassay. To isolate the lectin from G. angustifolia (GaL), it was proposed to treat the crude extract with ammonium sulfate, followed by chitin column chromatography. GaL was evaluated by denaturing electrophoresis (SDSPAGE). The extract showed important secondary metabolites such as the presence of phlobaphenic tannins, flavones, flavanols, xanthones, flavanones, steroids and saponins, as well as the sample showed an increase in the percentage radical sequestration of DDPH, with an increase in the concentration of the sample (100 - 700 mg / mL). The extract at 50 mg showed a mortality rate of 50% of insects from T. castaneum, presenting a deterrent activity (50 and 100 mg) in addition to exerting antinutritional effects on the conversion of biomass and insect growth. GaL was isolated after eluting the chitin column with 1 M acetic acid, showing itself as a protein with 18.4 kDa with hemagglutinating activity inhibited by N-acetylglycosamine, maltose and fetuin. The studied lectin showed thermostability, maintained hemagglutinating activity in acidic and slightly basic medium up to pH 8 and in the presence of magnesium, calcium and EDTA ions. The bioassay involving GaL showed low food deterrence. Only 10% mortality of adult insects was observed at the highest dose studied (1 mg), but it negatively affected the nutritional physiology of insects in addition to reducing the number of hatched larvae. Thus, aqueous preparations of G. angustifolia stem containing lectin showed insecticidal potential for population control of T. castaneum.