Avaliação da bioatividade dos óleos essenciais de 'eucalipto urocan' (Eucalyptus urophyla × Eucalyptus camaldulensis) e eucalipto benthami (Eucalyptus benthamii) sobre Sitophilus zeamais (COLEOPTERA: CURCULIONIDAE)

Abstract

The maize weevil, Sitophilus zeamais, is one of the most important insect-pest for culture. Because of the problems with contamination caused by the use of chemicals in the control of S. zeamais, the use of essential oils as an alternative to the use of these, has been studied. The species of the genus Eucalyptus, Eucalyptus benthamii and 'Eucalyptus urocan', are highly rich in essential oils and constituents toxic to insects. The objective of this study was to assess the bioactivity of essential oils of the Eucalyptus genus on S. zeamais in stored corn. The bioassays were conducted in a completely randomized experimental design with five replicates and performed two tests with each essential oil (preference and mortality index). For ‘Eucaliptus urocan’, five treatments were used, at doses of 10, 20, 30 and 50 μL and the witness, being used 20 adult insects of S. zeamais, not sexed, between the ages of 10 and 30 days per petri dish. The assessment of essential oil was performed at the times of 0, 24, 48, 72, 96 and 120 h. For the preference index tests, five arenas were used, using plastic pots which together consisted of a central pot connected symmetrically through plastic tubes to the other five pots diagonally. In the central container were placed 50 non-sexed adult insects and in the others 10 grams of corn kernels, treated with doses of 10, 20, 30 and 50 μL of essential oil, and the witness. The evaluation was done in times of 0, 24, 48, 72, 96 and 120 h. For E. benthamii the experiments were exactly the same, changing for both the mortality test and the preference index, six treatments at the dosages of 10, 20, 30, 50 and 100 μL, and the witness, respectively. Both species had effects on S. zeamais mortality of. ‘Eucaliptus urocan’ showed effects of high mortality at all doses, with the dose of 50 μL being the most efficient, presenting a 100% average mortality in its first 24 h. For E. benthamii, the highest mortality rate was obtained at higher doses and longer exposure times, achieving a mean mortality of 98.6% for the dose of 100 μL and 79% for the 50 μL dose. Regarding the preference index, ‘E. urocan’ presented an insect repellent effect at all doses, regardless of the exposure period, for E. benthamii the repellency was higher in larger doses and longer exposure periods. Thus, both ‘E. urocan ' and E. benthamii showed bioactivity insecticidal and repellency for S. zeamais.