Insecticidal activity of cerrado plant extracts on Rhodnius milesi Carcavallo, Rocha, Galvão & Jurberg (Hemiptera: Reduviidae), under laboratory conditions.

Chagas' disease is chiefly transmitted by feces of haematophagous bugs (Triatominae) that ingested Trypanosoma cruzi from blood of infected people or animals. Pyrethroids have been the main insecticides used against these insects. However, some populations of insects have shown significant levels of resistance to several pyrethroids, indicating the need of new insecticides for the control of triatomines. Insecticidal activity of 24 Cerrado plant extracts belonging to five species of four families were assayed on fourth instar nymphs of Rhodnius milesi Carcavallo, Rocha, Galvão & Jurberg (Hemiptera: Reduviidae), under laboratory conditions. For the extract application on triatomines, 50 microg of the extract were topically applied in duplicate on dorsal tergites of ten insects. Insects topically treated with acetone, ethanol, as well as insects with no treatment were used as controls. Triatomines were observed over a 28-day period. Hexanic and ethanolic extracts of Simarouba versicolor, Guarea kunthiana, Guarea guidonia and Talauma ovata caused mortality between 20% and 95% of R. milesi in comparison with the controls, which showed no insect mortality. These preliminary data suggest that the ethanolic extract of the root bark of S. versicolor and the hexanic extract of the root of G. guidonia, responsible for a 95% and 75% insect mortality, respectively, should be chemically investigated and monitored through biological assays in order to determine their insecticidal components, that could be used as a molecular model or as biorational compounds for use in insect control programmes.