Atividade do óleo essencial de Eugenia uniflora L. (Myrtaceae) sobre Sitophilus zeamais Mots. (Coleoptera: Curculionidae)

Abstract

The grain storage is susceptible to pest-insects attack, especially on corn weevil, Sitophilus zeamais (Coleoptera: Curculionidae). For control these pests, are used synthetic insecticides, which leave residues, bringing problems to human health and the environment. In order to reduce to use synthetic chemical insecticides, new control strategies have been studied, like the use of essential oils with insecticidal effect. Thus, the objective this work was to evaluate the insecticidal and repellent effect of Eugenia uniflora (Myrtacea) essential oil on S. zeamaisand to identify the chemical compounds of this oil. For that, four experiments were carried out: three for the evaluation of the insecticidal effect and one for repellent effect. In the experiments to evaluate the insecticidal effect, the oil was applied by the immersion method on the insect, volatilization and spraying on corn grains. For this, different concentrations of E. uniflora oil (0; 0.31; 0.62; 1.25; 2.5; 5; 10%) diluted with distilled water whith Tween 80% (0.01%) were prepared. Seven Petri dishes (replicates) were prepared per treatment and, on each dishes, 15 non-sexed insects were conditioned up to 60 days old. The dishes were kept in a climatic chamber at a temperature of 27 ± 2 ° C, HR: 60 ± 10% and photoperiod of 12 hours. For the immersion and spraying experiment, the evaluations were performed at intervals of 1; 6; 12; 24; 48; 72; 96 hours. Already for the volatilization experiment, the evaluation was done in the intervals of 12; 24; 48; 72 and 96 hours, quantifying the dead insects. For the repellency experiment the E. uniflora oil was evaluated in the concentration at 2.5% in an arena with four plastic containers interconnected by transparent tubes in a central containers. In two containers the grains corn was sprayed with the oil and in two the corn was sprayed with distilled water and 30 insects were released in the central container. The experiment was maintained under the same conditions described above. The evaluation was performed after 24 hours, quantifying the number of insects in each container. In order to identify the chemical compounds of the essential oil, Gas Chromatography analysis was performed in Mass spectrometer. It was found, in immersion experiment, mortality of caused in concentration 10%, differing signify cautly, from the control. In the volatilization experiment, there was no significant mortality within and between the times, in any of the treatments. In the corn grains spreying experiment, were found that concentrations 2.5%, 5% and 10% caused highest mortality rates, respectively, of 85.71%, 100% and 100%, differing from the control and treatment at the concentrations of 0,31%. The 2.5% E. uniflora oil has a repelente effect for S. zeamais adults. Regarding the identification of the essential oil compounds were found the major compounds, were sesquiterpenes of Calamen-10-one and Silfiperferol-6-in-5-one. The E. uniflora essential oil has insecticidal and repellent potential on S. zeamais, containing sesquiterpenes as major constituents.