Acaricidal and tyrosinase inhibitory activities of Tagetes verticillata Lag. & Rodr

Abstract

Tagetes verticillata Lag. & Rod.is an andean plant with ethnobotanical uses in Colombia, but there is not scientific research literature devoted to it. Tetranychus urticae Koch is a highly polyphagous species with 1059 host plants reported worldwide [1]. In this work, we obtained extracts from T. verticillata by percolation at room temperature using as solvents petroleum ether (PET), ethanol (ET) and ethyl acetate (EAT). The acaricidal activity of extracts was measured over adult females and nymphs of T. urticae. Also, egg-hatching inhibition was measured. The tyrosinase inhibitory activity of the extract with the highest acaricidal activity was measured. From PET extract we found significant and increasing mortality through the measuring periods (24, 48 and 72h), reaching mortality peaks for nymphs of 84.4% (1000 µg/mL) and for adults of 68.9% (5000 µg/mL). PET extract also caused 78.6% of inhibition of egg hatching (1000 µg/mL). Using PET extract we carried out a bioguided fractionation, obtaining the most active fraction over the mite. From that fraction we recorded a CL50 of 1162.7 ± 146.8 µg/mL (72h) for adults. Also, that fraction had an IC50 value of 150.7 ± 5.3 µg/mL for tyrosinase inhibitory activity. Using GC-MS, from PBT most active fraction, we identified 2,6-di-t-butyl-octahydroazulene-3-alpha as a major component. Other compounds identified in PBT extract were 9,12,15 octadecatrienoic acid as well as its ethyl ester derivative. It was also possible to identify complex mixtures of fatty acids whose main component was oleic acid. We concluded that the PET extract has a nymph-specific acaricidal activity of T. urticae and an inhibitory activity of egg-hatching. The gradual increase in mortality could be caused by a decrease of mite natural defences, on the basis of the inhibitory activity of tyrosinase found in our research and the role of this enzyme in the biosynthesis of melanin and other defensive substances in arthropods [2].