Insecticidal Activity of Individual and Mixed Monoterpenoids of Geranium Essential Oil against Pediculus humanus capitis (Head Lice)

GALLARDO A; PICOLLO M; GONZALEZ AUDINO P; GASTÓN MOUGABURE CUETO

JOURNAL OF MEDICAL ENTOMOLOGY

ENTOMOLOGICAL SOC AMER

Año: 2012 vol. 49 p. 332 - 335

0022-2585

The major components of the geranium essential oil were tested for synergy of the complex mixture for pediculicide activity. Chemical analysis of the geranium essential oil by gas chromatography coupled to mass spectrometry, revealed four major constituents (concentration expressed as percentage of total): citronellol (38%), geraniol (16%), citronellyl formate (10.4%) and linalool (6.45%). The contact insecticidal activities of major constituents against female Pediculus humanus capitis demonstrated that the most potent were citronellol and geraniol, with LD50 values 9.71 and 12.7 µg/i. Linalool and Citronellyl formate were less toxic with LD50 values 24.73 and 38.47 µg/i, in spite of the overlapping of their confidence intervals. The toxicity of an artificial mixture based on these major constituents in the same proportion they are in the natural oil, was higher than the whole oil and each individual component. To corroborate the role of the major constituents towards the total toxicity of geranium essential oil, each individual constituent was sucesively eliminated from the synthetic mixture. The removal of any constituent produced a decreased in effectiveness. The absence of citronellol caused the highest decrease in toxicity (DL50 from 2.21 to 10.9 µg/i), leading us to conclude that this constituent is the major contributor to the oil toxicity. The knowledge of the role of each constituent in the toxicity of the whole oil gives the possibility to create artificial blends of different constituents for the development of more effective control agents.