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Influence of essential oils on toxicity and pharmacokinetics of the plant toxin thymol in the larvae of Trichoplusia ni1

Published online by Cambridge University Press:  02 April 2012

Joanne A. Wilson  and
Murray B. Isman
Joanne A. Wilson
Affiliation:
Faculty of Land and Food Systems, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4
Murray B. Isman*
Affiliation:
Faculty of Land and Food Systems, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4
*
3 Corresponding author (e-mail: murray.isman@ubc.ca).
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Abstract

The present study was undertaken to determine the influence of some major constituents of plant essential oils on the toxicity and fate of thymol, a phenolic monoterpene from garden thyme (Thymus vulgaris L.) (Lamiaceae), following topical administration to the cabbage looper, Trichoplusia ni (Hubner) (Lepidoptera: Noctuidae). Tested individually, trans-anethole (LD50 = 71.2 µg/larva) and methyl salicylate (93.6 µg/larva) were the most toxic, whereas phenylethyl propionate (555.8 µg/larva) and mineral oil (2279.3 µg/larva) were the least toxic. However, when coadministered, mineral oil was the most synergistic (synergy ratio, SR = 25). A proprietary blend of essential oils (A4 Blend) was strongly synergistic (SR = 9), as was trans-anethole (SR = 5), while the majority of the other compounds tested yielded SRs of 2–3. Based on experiments using tritiated thymol as a radiotracer, the fate of this plant toxin within 60 min of topical administration varied widely with the essential oil carrier. Some carriers facilitated rapid disappearance of thymol from the insects' integument and rapid appearance internally, whereas others prolonged the tenure of thymol on the integument and delayed entry into the insect. The highest internal levels of radioactivity were observed when phenylethyl propionate was the carrier (47% of the topical dose), the lowest when rosemary oil was the carrier (9%). The highest proportion of the dose was excreted when eugenol was the carrier (20% of the topical dose), the lowest when mineral oil was the carrier (4%). Overall, there are no apparent trends linking the fate of thymol in the different carrier oils to the synergies observed or to the relative polarities of the carriers.

Résumé

Cette étude vise à déterminer l'influence de certains composés majeurs d'huiles essentielles de plantes sur le sort et la toxicité du thymol, un monoterpène phénolique du thym commun (Thymus vulgaris L.) (Lamiaceae), contre la fausse-arpenteuse du chou, Trichoplusia ni (Hubner) (Lepidoptera : Noctuidae), suite à une application topique. Testé individuellement, l'anéthol-trans (DL50 = 71.2 µg/larve) et le salicylate de méthyle (93.6 µg/larve) occasionnent les plus forts effets toxiques, tandis que le proprionate phényléthylique (555.8 µg/larve) et l'huile minérale (2279.3 µg/larve) sont les moins toxiques. Par contre, lorsque simultanément administré, l'huile minerale démontre le plus grand effet synergique (rapport de synergie (RS) = 25). Un mélange breveté d'huiles essentielles (Mélange A4) démontre un fort effet synergique, de même que l'anéthole-trans (RS = 5), alors que la majorité des autres composés testés démontrent des RS de 2–3. Lors d'expériences utilisant du thymol tritié comme indicateur radioactif, le sort de cette toxine d'origine botanique à l'intérieur de 60 min après une application topique varie grandement dépendamment des différentes sortes d'huiles essentielles utilisées comme support. Certains supports facilitent la disparition rapide du thymol du tégument des insectes avec une apparition interne accélérée, tandis que d'autres supports prolongent la persistance du thymol sur le tégument et retardent sa pénétration dans l'insecte. Le plus haut niveau de radioactivité interne est observé lorsque le propionate phényléthylique est utilisé comme support (47 % de la dose topique), alors que l'huile de romarin donne le plus bas niveau (9 %). On observe la plus grande proportion de la dose excrétée lorsque l'eugénol est utilisé comme support (20 % de la dose topique), alors que la plus petite est observé lorsque l'huile minérale est utilisé (4 %). Dans l'enssemble, il n'y a pas de tendance évidente entre le sort du thymol dans les différentes huiles de support et les niveaux de synergie observés ou la polarité relative des supports.

Type
Articles
Information
The Canadian Entomologist , Volume 138 , Special Issue/Numéro spécial 4: Honouring Geoffrey G. E. Scudder/En hommage à Geoffrey G.E. Scudder , August 2006 , pp. 578 - 589
Copyright
Copyright © Entomological Society of Canada 2006

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Footnotes

1

This paper is part of a special issue honouring Geoffrey G.E. Scudder for his significant contributions to entomology in Canada.

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