Insecticidal activity of essential oil of Lepechinia chamaedryoides (Balb.) Epling in Drosophila melanogaster

Abstract

With the aim to assess its biological activity, three extracts of a Chilean endemic plant, Lepechinia chamaedryoides (Balb.)
Epling (polar extract, resinous exudate and essential oil) were evaluated for its insecticidal activity on Diptera larvae,
Drosophila melanogaster Meigen. The bioassay was conducted on the basis of a completely randomized experimental
design with 15 treatments and three repetitions, which includes the study of mortality variables and 50% lethal concentration
(LC50) and 90 % (LC90), in addition to the observation of organisms through a magnifying glass, optical microscopy and
transmission electronic microscopy. Mortality was recorded over than 90 % in four tested concentrations of essential oil.
In the case of polar extract and resinous exudate no significant differences between the different concentrations tested and
controls, with mortality values lower than 23 %. The lethal concentration 50% (LC50) of essential oil was 0,46 % v/v and
the lethal concentration 90% (LC90) of 0,77 % v/v. There were changes in the external and internal morphology of the
third stage larvae. Externally, there was darkening of the cuticle and a volume increase of the body. Internally, there was a
fragmentation of the salivary glands as well as differences in the Malpighian tubes and imaginal discs in relation to control
group. At the cellular level, there were also changes, including changes in organelles like in rough endoplasmic reticulum,
mitochondria and Golgi apparatus.