Insecticidal effect of the ethanol extract of Baccharis dracunculifolia (Asterales: Asteraceae)
Insecticides from plants have been studied as an alternative in agricultural production and in vector control of human diseases. The use of botanical insecticides may cause mortality in different stages, slow growth, infertile adults and decrease in viability of insect eggs. This study aimed to analyze the insecticidal potential of ethanol extract of Baccharis dracunculifolia DC, on Spodoptera frugiperda Smith, 1797 (Noctuidae) and Aedes aegypti L., 1762 (Culicidae). The botanical material was collected and prepared on February 8th, 2011 on the Fazenda Escola Três Barras (20°33’37.44043" S - 54°32'10.3824" W), Campo Grande, MS. The ethanol extract was prepared from dried leaves obtained of adult plants in a vegetative state at the Chemistry Laboratory of Anhanguera University-Uniderp. The experiments of biological activities were conducted at the Entomology Laboratory of the Catholic University Don Bosco, in a controlled environment with an average temperature of 25 ºC and photoperiod 12 hr. Experiments with S. frugiperda were conducted from August to October 2014. The collection of A. aegypti eggs was made in January 2014 and the treatments were done from March 10th to 17th, 2014. In the development of S. frugiperda the extract caused effect on caterpillars subjected to treatment at one and 10 days. The larval stage proved to be longer at both ages and pupal weight reduced at 10 days, as well as increased mortality at one day, when incorporated concentration 0.2 % into diet. The variables studied were mortality, larval duration, pupal weight, number and viability of the eggs. The bioassay used A. aedes third instar, 25 larvae per concentration, at four replicates. Parameters analysed for sublethal doses were pupal and larval, mortality, length larval and young (larva + pupa) the ethanol extract at concentrations 0.5 mg.mL-1 and 0.25 mg.mL-1. The extract resulted in deleterious effect on the development of caterpillars undergoing treatment in larvae of one and 10 days of age, the larval stage stretching, lower pupal weight in caterpillars 10 days and higher mortality in the group with one day of life. It did not interfere with the viability of eggs. In the life cycle of A. aegypti, the extract of B. dracuncufolia at the studied concentrations caused delay in the development of larval and pupal stages, and inhibited the emergence of adults in 85 % and 70 %. In laboratory conditions it can be said that the ethanol extract of B. dracunculifolia has a potential insecticide effect for both species of insects.