Caracterização química e bioatividade dos óleos essenciais de Croton tricolor Klotzsch ex Baill. (Euphorbiaceae)

Abstract

Essential oils derived from aromatic plants are composed by complex mixtures of chemical components and are less likely to leave residues in stored products, representing minimal risk to the environment and health. Therefore, these compounds are gaining wide interest from researchers for pest control in stored products. Tribolium castaneum Herbst. (Coleoptera: Tenebrionidae) is one of the stored products pests recognized for having one of the greatest population growth potentials among these insects. Through a patent review study on insecticide products to control this species, the need to develop new technologies from natural products was identified. Thus, this study aims to evaluate the insecticidal and repellent potential of essential oils from leaves and branches of Croton tricolor Klotzsch ex Baill against Tribolium castaneum. The essential oils of leaves and branches of C. tricolor were obtained by hydrodistillation in Clevenger equipment and the chemical characterization was carried out by gas chromatography coupled with mass spectrometry. The evaluation of the repellency potential was developed based on the area preference method and a contact toxicity bioassay was carried out with concentrations of 1, 5 and 10% of essential oils. The effects of essential oil on nutritional indexes, on the metabolism and reproduction of T. castaneum after exposure to LD50 were evaluated. The C. tricolor essential oils showed a yield of 0.20% for branches and 0.66% for leaves and major compounds included caryophyllene (11,64%), sphatulenol (11,60%) e γ-elemene (11,47%) in leaves and guaiol (9,02%), β-elemene (7,63%) e dihydroagarofuran (7,20%) in branches. Repellency potential was identified against T. castaneum at all times of exposure, with a class ranging from IV to V, being the essential oil of C. tricolor leaves responsible for higher repellency potential. The contact toxicity tests resulted in an LD50 of 0,262 mg/larvae and 0,219 mg/adult for the essential oil of branches and 0,151 mg/larvae and 0.092 mg/adult for essential oil of leaves. Exposure to C. tricolor essential oils in adults caused an increase in the relative consumption of food, but without an increase in biomass, being accompanied by a significant reduction in cholesterol levels, especially in those who died after exposure. Larvae have a different metabolic response, characterized by increased levels of cholesterol, triglycerides and glucose in individuals who died after exposure. No reproductive effects from contact exposure have been identified. The results of this study point out that C. tricolor essential oils are promising alternatives for the control of the insect pest T. castaneum in stored products and toxicity in adults seems to be related to the inhibition of cholesterol uptake, but in larvae the deleterious effects resulted in greater metabolic demand, probably causing access to energy sources stored in the fat body, indicating that more than one mechanism of action may be involved on the insecticidal potential of C. tricolor.