Insecticidal Activity of Individual and Mixed Monoterpenoids of Geranium Essential Oil Against Pediculus humanus capitis (Phthiraptera: Pediculidae)

Abstract

The major components of geranium (Geranium maculatum L.) oil and their mixtures were tested against female Pediculus humanus capitis De Geer (Phthiraptera: Pediculidae). Chemical analysis by gas chromatography coupled to mass spectrometry revealed four major constituents: citronellol (38%), geraniol (16%), citronellyl formate (10.4%), and linalool (6.45%) (concentration expressed as percentage of total). Topical application demonstrated that the most potent component was citronellol and geraniol, with LD50 values 9.7 and 12.7 microg/insect, respectively. Linalool and Citronellyl formate were less toxic with LD50 values 24.7 and 38.5 microg/insect, respectively. Toxicity of these four major constituents in the same proportion as the natural oil, was greater than whole oil and each individual component. Removal of any four constituents produced a decreased in effectiveness. The absence of citronellol caused the greatest decrease in toxicity (DL50 from 2.2 to 10.9 microg/insect), leading us to conclude that this constituent is the major contributor to 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.

Terpenes: Natural Products for Controlling Insects of Importance to Human Health—A Structure-Activity Relationship Study

“…Among the components of essential oils, 1,8-cineole, anisole, limonene, -pinene, linalool, menthone, -pinene, pulegone, and myrcene have demonstrated fumigant activity (KT 50 < 53 min) whereas eugenol, borneol, menthol, isomenthol, anethole, camphor, carvone, menthyl acetate, linalyl acetate, thymol, p-cymene, -terpinene, -terpineol, and 4-terpineol had no effect (KT 50 > 60 min) [3,11,13,19,20]. Moreover, Gonzalez-Audino et al [34] and Gallardo et al [35] reported that citronellol and geraniol had the highest toxicity on adults for immersion and topical application methods, respectively. It has been suggested that the mechanism of action of essential oil components could be due to competitive inhibition of the enzyme acetylcholinesterase (AChE, EC 3.1.1.7).…”

“…The use of essential oils permits interaction with different targets simultaneously as a result of chemical diversity, although chemical diversity of an essential oil with a high bioactivity is difficult to reproduce. An artificial mixture of terpenes or phenylpropene has demonstrated a high activity and could have synergistic effects [35,39], with linalyl acetate mixed with other terpenes showing a better synergistic effect on the inhibition of AChE activity than many isolated compounds.…”

Insecticidal activity of citronella grass essential oil on Frankliniella schultzei and Myzus persicae

“…Monoterpenes present in the oil, such as limonene, citronellal and geraniol activate plant chemical defenses against insect pests (IBRAHIM et al, 2001;HUMMELBRUNNER;ISMAN, 2001;GALLARDO et al, 2012 …”

Synergism of thymol, carvacrol and eugenol in larvae of the cattle tick, Rhipicephalus microplus, and brown dog tick, Rhipicephalus sanguineus

“…Some studies have demonstrated that mixtures of different substances of plant origin have synergistic actions against bacteria (Didry et al, 1994), nematodes (Ntalli et al, 2011) and insects (Pavela, 2010;Gallardo et al, 2012). Recently, Novato et al (2015) investigated the interaction of combinations of carvacrol, thymol and (E)-cinnamaldehyde in larvae of Amblyomma sculptum Berlese, 1888 (Acari: Ixodidae) and D. nitens and observed a synergistic effect of the thymol + carvacrol combination.…”